SNIPE

UniProt ID: A0A8T9CRB7
Organism: Escherichia coli
Review Status: DRAFT
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Gene Description

SNIPE (Surface-associated Nuclease Inhibiting Phage Entry) is a 500 amino acid inner membrane-bound GIY-YIG family DNA endonuclease that provides direct anti-bacteriophage defence in Escherichia coli. SNIPE constitutively localizes to the inner membrane via an N-terminal single-pass transmembrane helix (aa 5-24) and pre-associates with the ManYZ mannose permease complex before phage infection. During phage genome injection, the central DUF4041 domain (aa 144-262, now designated the SNIPE-associated domain, IPR025280) binds both incoming phage DNA and the phage tape measure protein (TMP), positioning the C-terminal GIY-YIG nuclease domain (aa 357-450, catalytic residue E414) to cleave phage DNA as it crosses the inner membrane. This provides direct defence β€” the infected cell survives β€” in contrast to abortive infection systems. SNIPE does not affect phage adsorption, does not target pre-existing intracellular phage genomes (lysogens), and does not block plasmid transformation, indicating its activity is specific to the phage genome injection process. Originally identified as PD-lambda-1 in a functional screen of 71 diverse E. coli pangenomes (PMID:36123438), SNIPE homologues (~500 curated) are found across many bacterial phyla, with 33% of well-sequenced clades harbouring at least one homologue. The N-terminal region is highly variable and functions as a phage-specificity adapter, with 59% of homologues having one TM domain, 7% having two, and 34% using alternative membrane-targeting strategies (DivIVA domains, type III secretion domains, PH domains). SNIPE represents a previously unknown self/non-self discrimination strategy based on subcellular localization rather than sequence recognition (CRISPR-Cas) or modification detection (restriction-modification). Note: UniProt entry A0A8T9CRB7 is from E. coli strain T0181B.E-10. The experimentally characterized SNIPE was from strain MOD1-ECOR26 (GenBank RCP76574.1, locus APT27_20780). Both share RefSeq WP_001606968.1. SNIPE is not present in E. coli K-12 MG1655.

Proposed New Ontology Terms

SNIPE defense system

Definition: A defense response to a virus in which a membrane-anchored nuclease of the SNIPE family cleaves viral DNA during genome injection across the cell membrane. SNIPE proteins associate with inner membrane components at phage genome injection sites, bind phage tape measure proteins via their DUF4041 domain, and use a GIY-YIG nuclease domain to degrade incoming phage DNA before it enters the cytoplasm. Unlike restriction-modification or CRISPR-Cas systems, self/non-self discrimination is achieved through subcellular localization at the membrane rather than recognition of specific DNA sequences or modifications.

Justification: The current anti-foreign nucleic acid branch (GO:0099046 clearance of foreign intracellular nucleic acids) does not capture SNIPE mechanism, because SNIPE cleaves phage DNA during translocation at the membrane before the DNA becomes intracellular. A dedicated term under GO:0051607 (defense response to virus) is needed to represent this direct anti-phage mechanism.

Parent term: defense response to virus

Supporting Evidence:

antiviral defense by targeting viral nucleic acid

Definition: A defense response to a virus in which the host targets viral nucleic acid for degradation or modification, preventing viral replication. Includes systems that act on nucleic acid after cell entry (e.g. CRISPR-Cas, restriction-modification) and systems that act during genome injection (e.g. SNIPE).

Justification: Optional intermediate grouping term matching the GO issue proposal. This would provide a clean parent for nucleic acid-targeting anti-viral systems such as CRISPR-Cas, restriction-modification, and SNIPE while preserving mechanistic distinctions in child terms.

Parent term: defense response to virus

Supporting Evidence:

Existing Annotations Review

GO Term Evidence Action Reason
GO:0004520 DNA endonuclease activity
IDA
PMID:41741653
A membrane-bound nuclease directly cleaves phage DNA during ... 		NEW
Summary: SNIPE contains a C-terminal GIY-YIG nuclease domain (aa 357-450) that endonucleolytically cleaves phage DNA during genome injection. Substitution of the predicted catalytic residue E414 to alanine abolishes both nuclease activity and phage defence (PMID:41741653). Radiolabelled 32P phage DNA is degraded from ~42 kb to fragments <100 bp and mononucleotides in SNIPE-expressing cells, dependent on E414 (PMID:41741653). The pattern of degradation (smear of fragments rather than defined products) is consistent with endonucleolytic cleavage, though in vitro reconstitution has not yet been performed. The GIY-YIG nuclease domain is the most conserved region across ~500 SNIPE homologues (PMID:41741653), and domain-level homology to the T5orf172/MUG113 family of GIY-YIG endonucleases is confirmed by InterPro/Pfam assignments (IPR018306, PF13455). GO:0004520 is the appropriate level of specificity; there is no GIY-YIG-specific child term in GO, and the data do not support a more specific term like GO:0015666 (restriction endodeoxyribonuclease activity) since SNIPE does not recognize specific DNA sequences or modification states.
Reason: Core molecular function of SNIPE, directly demonstrated by multiple experimental approaches in PMID:41741653: (1) 32P-labelled phage DNA cleavage assay showing degradation during injection, (2) E414A catalytic dead mutant abolishing cleavage and defence, (3) Gam-GFP double-strand break reporter showing SNIPE-dependent foci, (4) CFP-ParB foci reduced ~30-fold indicating DNA degradation during injection. The domain architecture (GIY-YIG nuclease, IPR018306/PF13455) independently supports endonuclease activity via homology to biochemically characterized family members. IDA evidence code is appropriate because the nuclease activity was directly assayed in vivo using radiolabelled substrate and catalytic mutant controls.
Supporting Evidence:
PMID:41741653
we demonstrate that SNIPE directly cleaves phage DNA during genome injection
PMID:41741653
Using radiolabelled phage DNA and time-lapse microscopy to track phage genomes, we demonstrate that SNIPE directly cleaves phage DNA during genome injection
PMID:36123438
a putative membrane-anchored protein with a central coiled-coil domain (DUF4041) and a C-terminal DNA binding/cleavage domain
file:ECOLX/SNIPE/SNIPE-deep-research-falcon.md
T5orf172 is a subfamily of GIY-YIG endonucleases ... the two profiles [T5orf172 and MUG113] are highly related
GO:0003690 double-stranded DNA binding
IDA
PMID:41741653
A membrane-bound nuclease directly cleaves phage DNA during ... 		NEW
Summary: The DUF4041/SNIPE-associated domain (aa 144-262) of SNIPE has a positively charged surface that facilitates DNA binding. When the TM domain is removed (SNIPE(deltaTM E414A)-GFP), the protein co-localizes with the DAPI-stained nucleoid (Pearson R=0.76), and this co-localization is abolished when DUF4041 is also deleted (deltaDUF4041 shows R=0.13) (PMID:41741653). A DUF4041-only fusion to GFP also localizes to the nucleoid. ConSurf analysis shows the positively charged DNA-binding interface is conserved across SNIPE homologues (PMID:41741653). Note that the evidence for DNA binding is based on fluorescence microscopy co-localization with the nucleoid rather than a direct biochemical binding assay (e.g. EMSA); however, the domain-dependent co-localization pattern and the conserved positively charged surface provide strong support for direct DNA binding. Phage lambda DNA is dsDNA, making GO:0003690 the appropriate specific term. The original identification also noted the C-terminal region as a "DNA binding/cleavage domain" (PMID:36123438).
Reason: DNA binding by DUF4041 is demonstrated by microscopy showing domain-dependent nucleoid co-localization (PMID:41741653): removal of DUF4041 abolishes nucleoid association. This is further supported by the conserved positively charged surface identified by ConSurf analysis across ~500 homologues, and by domain annotation as a DNA-binding domain (IPR018306 Phage_T5_Orf172_DNA-bd). IDA evidence code is appropriate for microscopy-based localization experiments with domain deletion controls. The term GO:0003690 (double-stranded DNA binding) is preferred over GO:0003677 (DNA binding) because phage lambda DNA is dsDNA and the nucleoid is dsDNA.
Supporting Evidence:
PMID:36123438
a putative membrane-anchored protein with a central coiled-coil domain (DUF4041) and a C-terminal DNA binding/cleavage domain
GO:0051607 defense response to virus
IDA
PMID:41741653
A membrane-bound nuclease directly cleaves phage DNA during ... 		NEW
Summary: SNIPE provides direct defence against bacteriophage lambda and diverse siphoviruses. SNIPE-expressing cells survive phage lambda infection at high MOI where control cells lyse (PMID:41741653). Defence is demonstrated by: time-lapse microscopy showing cell survival, growth curves at MOI 0.1-10, plaque assays showing 6-7 log reduction in phage titre, and the BASEL collection screen showing protection against diverse siphoviruses (both ManYZ-dependent and ManYZ-independent) (PMID:41741653). SNIPE provides direct defence (cell survival) rather than abortive infection. It was originally identified as one of 21 novel defence systems in a functional metagenomic screen of the E. coli pangenome (PMID:36123438).
Reason: Defence against bacteriophage is the primary evolved biological function of SNIPE, supported by multiple complementary experimental approaches (PMID:41741653) and by its original identification via a functional anti-phage defence screen (PMID:36123438). GO:0051607 (defense response to virus) is the most specific existing BP term. There is currently no GO term for "defense response to bacteriophage" specifically; a new term request has been drafted (see projects/SNIPE/go-issue-antiviral-nucleic-acid-defense.md). IDA evidence code is appropriate as defence was directly assayed by growth curves, plaque assays, and single-cell microscopy.
Supporting Evidence:
PMID:41741653
we characterize SNIPE, an anti-bacteriophage defence system that constitutively localizes to the bacterial cell membrane in Escherichia coli to block phage
PMID:41741653
SNIPE as a widespread bacterial defence system that exploits the spatial organization of phage genome injection to specifically target viral DNA, representing a previously unknown strategy for distinguishing self from non-self in prokaryotic immune systems
PMID:36123438
Our results unveil 21 conserved defence systems, none of which were previously detected as enriched in defence islands
GO:0045071 negative regulation of viral genome replication
IDA
PMID:41741653
A membrane-bound nuclease directly cleaves phage DNA during ... 		NEW
Summary: SNIPE prevents phage genome replication by destroying the phage DNA during the injection process, before the genome enters the cytoplasm intact. CFP-ParB foci (a proxy for phage genome establishment) are reduced ~30-fold in SNIPE-expressing cells (PMID:41741653). Phage produced per cell is not significantly different between SNIPE and empty vector when inducing lysogens, confirming that SNIPE targets the injection step specifically and does not affect pre-existing intracellular phage genomes (PMID:41741653). While the net effect is prevention of viral genome replication, the mechanism is more precisely described as destruction of the phage genome during membrane translocation rather than regulation of replication per se. GO:0046597 (host-mediated suppression of symbiont invasion) may be a more mechanistically precise BP term since SNIPE blocks the entry/establishment of the phage genome rather than regulating its replication after entry.
Reason: The outcome of SNIPE activity is that viral genome replication is completely prevented, making GO:0045071 a defensible annotation. The evidence is strong: CFP-ParB foci reduction demonstrates that phage genomes do not establish in SNIPE-expressing cells (PMID:41741653). However, SNIPE acts upstream of replication -- it destroys the DNA during injection, not by regulating the replication machinery. This distinction may matter for precision. The annotation is retained because the net biological outcome (no viral genome replication) is accurately captured. See also the additional GO:0046597 annotation below for a more mechanistically precise complementary term. IDA evidence code is appropriate.
Supporting Evidence:
PMID:41741653
we demonstrate that SNIPE directly cleaves phage DNA during genome injection
PMID:41741653
SNIPE associates with host proteins essential for lambda genome entry and with the lambda tape measure protein, which facilitates lambda genome injection across the inner membrane
GO:0046597 host-mediated suppression of symbiont invasion
IDA
PMID:41741653
A membrane-bound nuclease directly cleaves phage DNA during ... 		NEW
Summary: SNIPE inhibits phage genome entry into the bacterial cell by cleaving phage DNA during the injection process at the inner membrane. This directly suppresses the phage's invasion of the host cell. GO:0046597 is defined as "a process in which a host inhibits or disrupts the entry of a symbiont into a host cell." While bacteriophages inject their genome rather than entering bodily, the phage genome translocation across the inner membrane constitutes the functional "entry" event that SNIPE suppresses. SNIPE does not block phage adsorption to the cell surface -- phage adsorption is unaffected (PMID:41741653) -- but it destroys the phage DNA during membrane translocation, preventing genome establishment. This term complements GO:0045071 by providing a more mechanistically precise description of SNIPE's biological role.
Reason: SNIPE acts specifically at the step of phage genome injection across the inner membrane (PMID:41741653). It does not affect phage adsorption, does not target pre-existing lysogens, and does not block plasmid transformation -- it is specific to the injection process. GO:0046597 (host-mediated suppression of symbiont invasion) captures this specificity better than GO:0045071 (negative regulation of viral genome replication), which implies action on the replication process itself. GO:0046597 is the parent of several relevant child terms in GO and is compatible with bacterial hosts defending against phage. IDA evidence code is appropriate.
Supporting Evidence:
PMID:41741653
we characterize SNIPE, an anti-bacteriophage defence system that constitutively localizes to the bacterial cell membrane in Escherichia coli to block phage
PMID:36123438
We confirmed that each system did not affect phage adsorption (Extended Data Fig
GO:0006308 DNA catabolic process
IDA
PMID:41741653
A membrane-bound nuclease directly cleaves phage DNA during ... 		NEW
Summary: SNIPE degrades phage DNA from ~42 kb to fragments less than 100 bp and mononucleotides during genome injection (PMID:41741653). This is a DNA catabolic process -- the breakdown of DNA. The 32P-labelled DNA tracking experiment directly demonstrates catabolism of the phage DNA substrate. While the MF annotation (GO:0004520 DNA endonuclease activity) captures the catalytic mechanism, GO:0006308 captures the biological process of DNA degradation that results from this activity.
Reason: The degradation of phage DNA from intact genomic molecules (~42 kb) to small fragments (<100 bp) and mononucleotides is directly demonstrated by the 32P-labelled DNA cleavage assay (PMID:41741653). This constitutes DNA catabolism. GO:0006308 provides a process-level annotation that complements the molecular function (GO:0004520) and the higher-level biological context (GO:0051607 defense response to virus). IDA evidence code is appropriate as the catabolic activity was directly measured using radiolabelled substrate.
Supporting Evidence:
PMID:41741653
we demonstrate that SNIPE directly cleaves phage DNA during genome injection
GO:0005887 integral component of plasma membrane
IDA
PMID:41741653
A membrane-bound nuclease directly cleaves phage DNA during ... 		NEW
Summary: SNIPE is an integral inner membrane protein with a single-pass TM helix (aa 5-24). Topology was confirmed by PhoA-LacZalpha fusion analysis: PhoA was active only when inserted at the N-terminus (periplasmic side), and LacZalpha was active only when inserted downstream of the TM domain (cytoplasmic side) (PMID:41741653). SNIPE-GFP localizes uniformly to the cell membrane by fluorescence microscopy (PMID:41741653). Immunoblotting of fractionated cell lysates shows SNIPE is strongly enriched in the membrane fraction (PMID:41741653). DeepTMHMM and Phobius both predict a transmembrane helix at residues 6-24, consistent with the UniProt annotation (ECO:0000256|SAM:Phobius). In bacteria, GO:0005886 (plasma membrane) corresponds to the inner/cytoplasmic membrane. The single-pass TM helix makes SNIPE an integral (not peripheral) component, supporting GO:0005887 over GO:0005886.
Reason: Integral membrane localization is directly demonstrated by three independent experimental approaches in PMID:41741653: (1) PhoA/LacZalpha topology mapping confirming transmembrane orientation, (2) fluorescence microscopy of SNIPE-GFP showing uniform membrane localization, (3) membrane fractionation/immunoblotting showing enrichment in membrane fraction. This is further supported by the predicted TM helix (Phobius, DeepTMHMM) in the UniProt record. GO:0005887 (integral component of plasma membrane) is preferred over GO:0005886 (plasma membrane) because the single-pass TM helix makes SNIPE an integral membrane protein. IDA evidence code is appropriate for the topology mapping and fractionation experiments.
Supporting Evidence:
PMID:41741653
an anti-bacteriophage defence system that constitutively localizes to the bacterial cell membrane in Escherichia coli
PMID:41741653
Here, we characterize SNIPE, an anti-bacteriophage defence system that constitutively localizes to the bacterial cell membrane in Escherichia coli to block phage Ξ» infection

Core Functions

SNIPE is a membrane-anchored DNA endonuclease that directly cleaves bacteriophage DNA during the genome injection process. It exploits the spatial organization of phage genome entry β€” the fact that phage DNA must cross the inner membrane β€” to distinguish foreign (viral) DNA from self (chromosomal) DNA. The GIY-YIG nuclease domain provides the catalytic endonuclease activity, with E414 as the essential catalytic residue. The DUF4041 domain binds both phage DNA (via a conserved positively charged interface) and phage tape measure proteins (TMPs), positioning the nuclease at the site of genome injection. The N-terminal TM domain anchors SNIPE to the inner membrane, preventing autoimmune cleavage of host chromosomal DNA. SNIPE pre-associates with the ManYZ mannose permease complex, which is the inner membrane conduit for lambda genome injection, ensuring SNIPE is positioned at genome entry sites before infection occurs. This provides direct defence β€” the infected cell survives β€” in contrast to abortive infection systems that sacrifice the infected cell. SNIPE also provides ManYZ-independent defence against diverse siphoviruses, probably through direct interactions with their TMPs via the DUF4041 domain. The ~500 SNIPE homologues across bacterial phyla show conservation of the GIY-YIG nuclease and DUF4041 domains, while the N-terminal region is highly diversified and functions as a phage-specificity adapter with varied membrane-targeting strategies (TM helices, DivIVA domains, T3SS domains, PH domains).

Molecular Function:
DNA endonuclease activity
Directly Involved In:
defense response to virus negative regulation of viral genome replication
Cellular Locations:
plasma membrane
Supporting Evidence:
  • PMID:41741653
    SNIPE as a widespread bacterial defence system that exploits the spatial organization of phage genome injection to specifically target viral DNA, representing a previously unknown strategy for distinguishing self from non-self in prokaryotic immune systems
  • PMID:36123438
    A functional selection reveals previously undetected anti-phage defence systems in the E. coli pangenome

References

PMID:41741653
A membrane-bound nuclease directly cleaves phage DNA during genome injection
  • SNIPE is a membrane-bound nuclease that directly cleaves phage DNA during genome injection, providing direct defence against bacteriophage
    "we demonstrate that SNIPE directly cleaves phage DNA during genome injection"
  • SNIPE constitutively localizes to the bacterial cell membrane
    "we characterize SNIPE, an anti-bacteriophage defence system that constitutively localizes to the bacterial cell membrane in Escherichia coli to block phage"
  • SNIPE pre-associates with host proteins for lambda genome entry and with the tape measure protein during genome injection
    "SNIPE associates with host proteins essential for Ξ» genome entry and with the Ξ» tape measure protein, which facilitates Ξ» genome injection across the inner membrane"
  • Radiolabelled phage DNA tracking demonstrates SNIPE cleaves DNA during injection
    "Using radiolabelled phage DNA and time-lapse microscopy to track phage genomes, we demonstrate that SNIPE directly cleaves phage DNA during genome injection"
  • SNIPE provides ManYZ-independent defence against siphoviruses via direct TMP interaction
    "SNIPE also defends against diverse siphoviruses, probably through direct interactions with their tape measure proteins"
  • SNIPE is a widespread defence system representing a novel self/non-self discrimination strategy
    "SNIPE as a widespread bacterial defence system that exploits the spatial organization of phage genome injection to specifically target viral DNA, representing a previously unknown strategy for distinguishing self from non-self in prokaryotic immune systems"
PMID:36123438
A functional selection reveals previously undetected anti-phage defence systems in the E. coli pangenome
  • SNIPE (originally PD-lambda-1) was identified in a functional metagenomic screen of 71 diverse E. coli strains as a novel anti-phage defence system
    "Our results unveil 21 conserved defence systems, none of which were previously detected as enriched in defence islands"
  • SNIPE is a membrane-anchored protein with DUF4041 and a GIY-YIG nuclease domain
    "a putative membrane-anchored protein with a central coiled-coil domain (DUF4041) and a C-terminal DNA binding/cleavage domain"
  • Defence systems including SNIPE are carried primarily by prophages and mobile genetic elements
    "intact prophages and mobile genetic elements are primary reservoirs and distributors of defence systems in E. coli"
file:ECOLX/SNIPE/SNIPE-deep-research-falcon.md
Deep research on SNIPE/DUF4041 domain-containing protein (falcon)
  • T5orf172/MUG113 (PF13455) is a GIY-YIG endonuclease subfamily; MUG113 profile is highly related to T5orf172, placing SNIPE's nuclease domain in the GIY-YIG HEG space
    "T5orf172 is a subfamily of GIY-YIG endonucleases ... the two profiles [T5orf172 and MUG113] are highly related"
  • T5orf172-family proteins have modular architecture with variable DNA-binding modules determining target specificity, paired with a conserved nuclease domain
    "a nuclease domain paired with variable DNA-binding modules that determine target specificity"

Suggested Questions for Experts

Q: Is GO:0004520 (DNA endonuclease activity) the correct MF term for SNIPE, or should a more specific child term (e.g. reflecting GIY-YIG family membership or the membrane-localized context) be used?

Q: Should the ManYZ pre-association be annotated as a separate protein complex, or is it better modelled as a GO-CAM causal association (SNIPE located_in plasma membrane, colocalizes_with ManYZ complex)?

Q: Does the tape measure protein (TMP) binding by DUF4041 warrant a specific MF annotation (e.g. viral protein binding) or is this better captured only in the GO-CAM model?

Suggested Experiments

Experiment: The 32P cleavage assay (Fig 2d) shows a smear of fragments consistent with endonucleolytic cleavage, but the exact cleavage mechanism and products have not been biochemically characterized with purified SNIPE. In vitro reconstitution of SNIPE nuclease activity with defined DNA substrates would confirm endonuclease vs exonuclease activity, determine sequence specificity (if any), and characterize cleavage products.

Hypothesis: SNIPE cleaves phage DNA endonucleolytically (producing internal cuts) rather than exonucleolytically

Type: Biochemical assay

Experiment: Test representative SNIPE homologues lacking TM domains for phage defence in their native hosts or heterologous expression. Determine whether these homologues also pre-associate with inner membrane proteins at genome injection sites, and whether their N-terminal domains dictate phage specificity.

Hypothesis: SNIPE homologues with non-TM N-terminal regions (DivIVA, T3SS, PH domain) use analogous mechanisms but target different phage entry pathways

Type: Genetics/Functional assay

Tags

anti-phage defence nuclease membrane protein innate immunity phage-host interaction

Deep Research

Falcon

(SNIPE-deep-research-falcon.md)
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 26 citations 2026-03-01T19:12:21.736197

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research Report: Functional Annotation of β€œSNIPE” (UniProt A0A8T9CRB7; ORF D4N09_22825) in Escherichia coli (ECOLX)

  1. Executive summary and identity verification

Target identity provided by the user specifies UniProt A0A8T9CRB7 as an E. coli protein described as β€œDUF4041 domain-containing protein,” with InterPro/Pfam domain annotations including Phage_T5_Orf172_DNA-bd (IPR018306), SNIPE (IPR025280; PF13250), and MUG113 (PF13455). In the tool-retrieved literature, β€œSNIPE” did not appear as an E. coli gene symbol nor as PF13250/IPR025280, and no publication directly referenced A0A8T9CRB7 or ORF D4N09_22825. Therefore, the current evidence base supports only domain-context-based functional inference and does not support an experimentally validated gene-specific function for this particular E. coli protein.

Critically, the only directly relevant and recent evidence recovered concerns the related T5orf172/MUG113 family, which is treated as a GIY‑YIG endonuclease subfamily and a common phage homing endonuclease gene (HEG) module. Barth et al. explicitly accept MUG113 (PF13455) for T5orf172 proteins because the profiles are highly related, supporting the interpretation that the MUG113-like part of the user’s protein is in the T5orf172-like HEG/nuclease space (https://doi.org/10.1101/2023.03.23.533998; posted 2023-03-23) (barth2023nucleasegenesoccupy pages 3-4).

  1. Key concepts and definitions (current understanding)

2.1 Homing endonuclease genes (HEGs)

HEGs are β€œselfish” mobile elements that spread by introducing site-specific DNA breaks in homologous target loci lacking the HEG, followed by repair via homologous recombination that copies the HEG into the cleaved allele (β€œhoming”). This canonical model is explicitly described and used as a conceptual framework for T5orf172-family proteins in both bacteriophage and eukaryotic-virus-associated mobile elements (https://doi.org/10.1093/ve/veae051; published 2024-07) (barth2024genomicanalysisof pages 8-10).

2.2 GIY‑YIG endonucleases and the T5orf172 subfamily

The GIY‑YIG endonuclease superfamily comprises catalytic nuclease domains used by diverse mobile elements, including many phage-associated HEGs. In the retrieved corpus, T5orf172 is described as a GIY‑YIG endonuclease subfamily: Barth et al. state β€œT5orf172 is a subfamily of GIY-YIG endonucleases,” and note that in at least one example, nuclease activity depends on a glutamate residue whose catalytic role is inferred from alignments to biochemically characterized GIY‑YIG enzymes (https://doi.org/10.1101/2023.03.23.533998; posted 2023-03-23) (barth2023nucleasegenesoccupy pages 6-10, barth2023nucleasegenesoccupy pages 4-6).

2.3 Modular architecture: DNA-binding + nuclease domains

A recurring theme in T5orf172-like HEGs is domain modularity: a nuclease domain paired with variable DNA-binding modules that determine target specificity. Barth et al. operationalize this by trimming sequences to separate terminal nuclease domains from putative DNA-binding termini and then annotating DNA-binding domains (CapR-like and Zn-finger DUFs; RepA_N) (barth2023nucleasegenesoccupy pages 4-6). Their figures visually summarize the β€œbeads-on-a-string” repeat architecture for DNA-binding modules followed by a terminal nuclease domain in representative T5orf172 HEGs (barth2023nucleasegenesoccupy media 643002a1, barth2023nucleasegenesoccupy media fc0baff9).

2.4 Phage satellites and phage–satellite conflict as a functional context

In Vibrio cholerae phage ICP1, and its satellites called PLEs (phage-inducible chromosomal island-like elements), there is an arms-race dynamic in which satellites inhibit phage production and phages counter-adapt. This system provides experimentally grounded examples where T5orf172-like nuclease modules (and HEG-derived DNA-binding modules) have clear functional roles in defense and counter-defense (barth2021achimericnuclease pages 12-14, barth2023nucleasegenesoccupy pages 18-20).

  1. Molecular function, biological process, and localization: what can be concluded for A0A8T9CRB7?

3.1 What is directly known for A0A8T9CRB7 (SNIPE in ECOLX)

No direct experimental evidence was retrieved for A0A8T9CRB7 itself, its gene/ORF D4N09_22825, or for PF13250/IPR025280 (β€œSNIPE”) in E. coli. Consequently, claims about its precise biochemical activity (e.g., a specific cleavage motif or substrate), its physiological pathway in E. coli, or its cellular localization cannot be made from the retrieved evidence set.

3.2 High-confidence inference from the closely related T5orf172/MUG113 domain context

Given (i) the explicit statement that MUG113 (PF13455) is β€œhighly related” to T5orf172 and accepted for T5orf172-containing proteins (barth2023nucleasegenesoccupy pages 3-4), and (ii) the repeated classification of T5orf172 as a GIY‑YIG endonuclease subfamily (barth2023nucleasegenesoccupy pages 6-10, barth2023nucleasegenesoccupy pages 4-6), the strongest defensible functional inference is:

β€’ The protein family context is consistent with a DNA endonuclease (GIY‑YIG-like) that is frequently embedded in mobile genetic elements (especially phages) and often functions as a homing endonuclease or as a domesticated derivative that targets specific DNA sequences (barth2024genomicanalysisof pages 8-10, barth2023nucleasegenesoccupy pages 10-12).

β€’ The functional β€œsubstrate class” in characterized systems is DNA, and specificity is typically determined by fused DNA-binding modules (e.g., RepA_N origin-binding domains or zinc-finger-like repeats related to CapR) (barth2023nucleasegenesoccupy pages 18-20, barth2023nucleasegenesoccupy pages 15-18).

β€’ Therefore, for A0A8T9CRB7, the most plausible primary molecular roleβ€”conditional on its domain architecture being homologous to these systemsβ€”is as a sequence-specific DNA-binding protein with a nuclease-associated region (or an HEG-derived DNA-binding module), potentially involved in mobile-element dynamics rather than core E. coli metabolism.

3.3 Likely cellular/biological compartment

Characterized T5orf172-like effectors and their domesticated derivatives act on DNA during phage infection or mobile-element activity; this implies intracellular action on nucleic acids (host or viral DNA), not secretion or membrane localization (barth2021achimericnuclease pages 12-14, barth2023nucleasegenesoccupy pages 18-20). However, localization for A0A8T9CRB7 in E. coli cannot be asserted without accession-specific evidence.

  1. Experimental anchors from related systems (authoritative sources)

Because A0A8T9CRB7 lacks direct evidence, the most useful annotation anchors come from experimentally characterized T5orf172-containing proteins in related phage/satellite systems.

4.1 Odn/Gp88: a modular origin-targeting nuclease with a T5orf172-like nuclease domain

Barth et al. (eLife, 2021-07; https://doi.org/10.7554/elife.68339) report that ICP1 isolates lacking CRISPR-Cas instead encode gp88, a T5orf172-domain protein (pfam10544) whose activity is consistent with a GIY‑YIG-like nuclease mechanism: it retains key catalytic residues and a conserved glutamate (E180) whose mutation (E180A) abolishes function (barth2021achimericnuclease pages 4-5, barth2021achimericnuclease pages 2-4). Functionally, gp88 is required for phage propagation on hosts carrying specific PLE variants (PLE1/4/5), linking the nuclease to anti-satellite immunity (barth2021achimericnuclease pages 4-5, barth2021achimericnuclease pages 2-4).

The same study provides direct substrate specificity evidence: purified Gp88 cleaves PCR fragments containing replication origin sequences from sensitive PLEs (PLE1/4/5) but not insensitive PLEs (PLE2/3) in vitro (assayed at 500 nM protein), and the catalytic-site mutant E180A abolishes cleavage (barth2021achimericnuclease pages 7-9). Mechanistically, Odn/Gp88 is presented as a chimeric nuclease in which DNA-binding specificity and nuclease function are separable modules; escape can occur via changes in iteron spacing/architecture, suggesting steric/spacing constraints similar to GIY‑YIG endonucleases (barth2021achimericnuclease pages 12-14).

4.2 CapR: domesticated HEG-derived DNA-binding module used for transcriptional repression

Netter et al. (Nucleic Acids Research, 2021-11; https://doi.org/10.1101/2020.11.28.402263) describe CapR as a small (15.5 kDa) satellite-encoded DNA-binding protein that represses the ICP1 capsid morphogenesis operon. EMSAs show CapR binds specifically to the capsid operon promoter region (binds probe A; not a control probe), and mapping indicates binding upstream of the promoter core elements (netter2021aphagesatellite pages 11-13). CapR-mediated repression is tuned: it downregulates capsid operon transcription by ~3-fold (producing roughly one-third as many capsid morphogenesis proteins) without measurably inhibiting ICP1 progeny production under tested conditions, whereas stronger repression via CRISPRi harms both phage and satellite mobilization (netter2021aphagesatellite pages 13-15, netter2021aphagesatellite pages 11-13).

CapR is linked bioinformatically to domains of ICP1 homing endonucleases, supporting an β€œexpert” evolutionary interpretation: a putative HEG-derived DNA-binding module was domesticated into a transcriptional repressor after nuclease loss, analogous to known HEG regulatory behaviors (netter2021aphagesatellite pages 13-15, netter2021aphagesatellite pages 15-16).

  1. Recent developments (prioritizing 2023–2024)

5.1 2023: Phage-wide genomics of T5orf172/MUG113 HEGs, domain architectures, and mobility statistics

Barth et al. (bioRxiv, posted 2023-03-23; https://doi.org/10.1101/2023.03.23.533998) provide large-scale comparative genomics of HEGs across phages, with emphasis on T5orf172. They report that T5orf172 HEGs are common across multiple phage clades and frequently occur in or near essential genes. Quantitative neighborhood statistics include 468 T5orf172 neighborhoods across 204 genomes, with 35% near terminase, 33% near ribonucleotide reductase, and 31% near capsid genes (barth2023nucleasegenesoccupy pages 10-12).

They also quantify DNA-binding module associations for T5orf172 HEGs: 95/229 (41.5%) encode a CapR-like domain, and 200/229 (87.3%) contain at least one of three Zn-finger-like domains (CapR, DUF723, or DUF4397), often as multiple repeats consistent with class V repeat proteins (β€œbeads on a string”) (barth2023nucleasegenesoccupy pages 15-18). These repetitive, modular architectures provide a mechanistic rationale for rapid specificity diversification via recombination and domain shuffling (barth2023nucleasegenesoccupy pages 15-18). Figures 5–6 visually depict these repeated DNA-binding domains linked to terminal nuclease modules and illustrate recombination events that generate deletions and domain swaps (barth2023nucleasegenesoccupy media 643002a1, barth2023nucleasegenesoccupy media fc0baff9).

Importantly for your target’s domain set: the authors explicitly state that for proteins with T5orf172 domains, they also accepted MUG113 (PF13455) because β€œthe two profiles are highly related,” providing the clearest support in this corpus that MUG113-like proteins fall into the T5orf172 HEG/nuclease domain space (barth2023nucleasegenesoccupy pages 3-4).

5.2 2024: T5orf172 as a mobile HEG module in eukaryotic-virus-associated elements

Barth et al. (Virus Evolution, 2024-07; https://doi.org/10.1093/ve/veae051) extend the T5orf172 framing beyond bacteriophages, describing T5orf172 as a GIY‑YIG subfamily domain and discussing its association with mobility, repeats, and recombination in hyperparasitic viruses (polinton-like viruses) associated with entomopoxviruses. They highlight hallmarks consistent with HEG-like mobility (multiple homologous copies, repetitive/modular architectures, flanking repeats, rearrangements) and explicitly define the HEG homing mechanism to interpret these patterns (barth2024genomicanalysisof pages 8-10). They further discuss possible β€œcollaborative homing” scenarios where HEGs mobilize nearby cargo and intron-associated elements, framing T5orf172-like endonucleases as contributors to module turnover and replicon evolution (barth2024genomicanalysisof pages 10-11).

  1. Applications and real-world implementations

6.1 Natural, deployable design principles for sequence-targeted nucleases

The Odn/Gp88 case demonstrates a naturally evolved β€œprogrammable-like” paradigm: a DNA-binding specificity module (RepA_N-like origin-binding domain) fused to a GIY‑YIG-like nuclease effector (T5orf172-like domain) creates a sequence/architecture-specific nuclease that targets satellite replication origins and provides immunity in the absence of CRISPR-Cas (barth2021achimericnuclease pages 7-9, barth2021achimericnuclease pages 4-5). This is relevant for synthetic biology and phage engineering conceptually, because it shows that modular domain shuffling can generate novel targeting specificities (barth2021achimericnuclease pages 12-14).

6.2 Transcriptional regulation and particle hijacking modules (phage satellite biology)

CapR represents a β€œdomesticated endonuclease-derived” DNA-binding module used to tune helper-phage gene expression to balance inhibition and satellite propagation (netter2021aphagesatellite pages 15-16, netter2021aphagesatellite pages 13-15). This is a real biological implementation of fine-tuned repression rather than maximal suppression.

6.3 Practical genome annotation and phage genomics

Barth et al. 2023 provides concrete quantitative heuristics used in annotation pipelines: detection of T5orf172/MUG113 domains via Pfam HMMs, trimming strategies to isolate nuclease vs DNA-binding termini, and the empirical prevalence of specific DNA-binding modules (CapR/DUF723/DUF4397; RepA_N) that co-occur with T5orf172-like nuclease domains (barth2023nucleasegenesoccupy pages 4-6, barth2023nucleasegenesoccupy pages 15-18). These are directly applicable to real-world functional annotation workflows for prophage and mobile-element proteins.

  1. Expert opinions and analysis (authoritative interpretations)

Across the retrieved works, the recurring expert interpretation is that T5orf172/MUG113-family genes are best viewed primarily through the lens of mobile-element biology (HEGs) rather than as stable, core cellular genes. Barth et al. emphasize the mobility signatures of these genes (presence/absence variation across isolates, frameshifts/deletions, intron/intein associations, proximity to essential genes) and caution that homology/domain presence does not automatically imply active β€œhoming,” because HEG-derived proteins can be domesticated for new roles (barth2023nucleasegenesoccupy pages 6-10, barth2023nucleasegenesoccupy pages 23-25). Netter et al. similarly frame CapR as a domesticated derivative of a putative homing endonuclease lineage, emphasizing repurposing of DNA-binding function after loss of nuclease function (netter2021aphagesatellite pages 13-15, netter2021aphagesatellite pages 15-16).

  1. Key statistics and data (recent studies)

Quantitative data points relevant to domain-family function and to annotation:

β€’ In phage neighborhood surveys: among 468 T5orf172 neighborhoods (204 genomes), 35% associate with terminase, 33% with ribonucleotide reductase, and 31% with capsid genes (Barth et al., bioRxiv posted 2023-03-23) (barth2023nucleasegenesoccupy pages 10-12).

β€’ DNA-binding module prevalence in T5orf172 HEGs: 95/229 (41.5%) encode a CapR-like domain; 200/229 (87.3%) encode at least one of CapR/DUF723/DUF4397 Zn-finger domains; many encode multiple repeats (barth2023nucleasegenesoccupy pages 15-18).

β€’ CapR/CRISPRi phenotypes (Netter et al., NAR 2021-11): CRISPRi targeting the capsid operon reduces capsid protein ~3-fold, reduces ICP1 plaquing efficiency to ~1/5, reduces ICP1 particle formation ~3-fold, and reduces PLE transduction by nearly an order of magnitude; in contrast, CapR-mediated repression does not inhibit ICP1 progeny despite ~3-fold transcriptional downregulation of the capsid operon (netter2021aphagesatellite pages 11-13, netter2021aphagesatellite pages 13-15).

β€’ Origin-selective cleavage by Odn/Gp88: purified protein cleaves origin-containing DNA fragments from some PLEs but not others, and catalytic mutant E180A abolishes cleavage/activity (barth2021achimericnuclease pages 7-9).

  1. What remains unknown for the specific E. coli protein A0A8T9CRB7 (SNIPE)

Given the lack of accession-specific literature in the retrieved corpus, the following points cannot be responsibly concluded for A0A8T9CRB7 without additional targeted database retrieval and/or experiments:

β€’ Whether A0A8T9CRB7 is encoded in a prophage region, plasmid, integrative element, or core chromosome.

β€’ Whether it is an active nuclease, a DNA-binding protein lacking nuclease activity, or another type of mobile-element accessory factor.

β€’ Its in vivo DNA targets, if any (e.g., origin sequences, repeat elements), and whether it participates in a recognizable E. coli pathway.

β€’ Subcellular localization beyond the generic expectation of intracellular nucleic-acid interaction implied by the domain context.

  1. Practical functional-annotation recommendation (evidence-constrained)

Based strictly on the retrieved evidence and the domain context provided by the user, a conservative, evidence-aligned annotation for A0A8T9CRB7 would be:

β€’ β€œPredicted mobile-element-associated DNA-binding protein with homing-endonuclease-related (GIY‑YIG/T5orf172/MUG113-like) nuclease domain architecture; likely involved in sequence-specific DNA interactions in prophage/mobile element contexts; function uncharacterized in E. coli.”

This phrasing aligns with the demonstrated behavior of T5orf172/MUG113 proteins as modular HEG-derived nucleases and DNA-binding proteins that can be domesticated for regulation or anti-satellite defense, while explicitly acknowledging that SNIPE (PF13250/IPR025280) and the specific UniProt accession were not directly covered by the retrieved literature (barth2023nucleasegenesoccupy pages 4-6, barth2023nucleasegenesoccupy pages 6-10, netter2021aphagesatellite pages 13-15).

References (URLs and dates)

β€’ Barth ZK, Dunham DT, Seed KD. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv. Posted 2023-03-23. https://doi.org/10.1101/2023.03.23.533998 (barth2023nucleasegenesoccupy pages 3-4, barth2023nucleasegenesoccupy pages 15-18, barth2023nucleasegenesoccupy pages 10-12).

β€’ Netter Z, Boyd CM, Silvas TV, Seed KD. A phage satellite tunes inducing phage gene expression using a domesticated endonuclease to balance inhibition and virion hijacking. Nucleic Acids Research. 2021-11. https://doi.org/10.1101/2020.11.28.402263 (netter2021aphagesatellite pages 11-13, netter2021aphagesatellite pages 13-15).

β€’ Barth ZK, Nguyen MHT, Seed KD. A chimeric nuclease substitutes a phage CRISPR-Cas system to provide sequence-specific immunity against subviral parasites. eLife. 2021-07. https://doi.org/10.7554/elife.68339 (barth2021achimericnuclease pages 7-9, barth2021achimericnuclease pages 4-5).

β€’ Barth ZK, Hicklin I, ThΓ©zΓ© J, et al. Genomic analysis of hyperparasitic viruses associated with entomopoxviruses. Virus Evolution. 2024-07. https://doi.org/10.1093/ve/veae051 (barth2024genomicanalysisof pages 8-10, barth2024genomicanalysisof pages 10-11).

References

  1. (barth2023nucleasegenesoccupy pages 3-4): Zachary K Barth, Drew T Dunham, and Kimberley D Seed. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv, Mar 2023. URL: https://doi.org/10.1101/2023.03.23.533998, doi:10.1101/2023.03.23.533998. This article has 20 citations.

  2. (barth2024genomicanalysisof pages 8-10): Zachary K Barth, Ian Hicklin, Julien ThΓ©zΓ©, Jun Takatsuka, Madoka Nakai, Elisabeth A Herniou, Anne M Brown, and Frank O Aylward. Genomic analysis of hyperparasitic viruses associated with entomopoxviruses. Virus Evolution, Jul 2024. URL: https://doi.org/10.1093/ve/veae051, doi:10.1093/ve/veae051. This article has 6 citations and is from a peer-reviewed journal.

  3. (barth2023nucleasegenesoccupy pages 6-10): Zachary K Barth, Drew T Dunham, and Kimberley D Seed. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv, Mar 2023. URL: https://doi.org/10.1101/2023.03.23.533998, doi:10.1101/2023.03.23.533998. This article has 20 citations.

  4. (barth2023nucleasegenesoccupy pages 4-6): Zachary K Barth, Drew T Dunham, and Kimberley D Seed. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv, Mar 2023. URL: https://doi.org/10.1101/2023.03.23.533998, doi:10.1101/2023.03.23.533998. This article has 20 citations.

  5. (barth2023nucleasegenesoccupy media 643002a1): Zachary K Barth, Drew T Dunham, and Kimberley D Seed. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv, Mar 2023. URL: https://doi.org/10.1101/2023.03.23.533998, doi:10.1101/2023.03.23.533998. This article has 20 citations.

  6. (barth2023nucleasegenesoccupy media fc0baff9): Zachary K Barth, Drew T Dunham, and Kimberley D Seed. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv, Mar 2023. URL: https://doi.org/10.1101/2023.03.23.533998, doi:10.1101/2023.03.23.533998. This article has 20 citations.

  7. (barth2021achimericnuclease pages 12-14): Zachary K Barth, Maria HT Nguyen, and Kimberley D Seed. A chimeric nuclease substitutes a phage crispr-cas system to provide sequence-specific immunity against subviral parasites. eLife, Jul 2021. URL: https://doi.org/10.7554/elife.68339, doi:10.7554/elife.68339. This article has 46 citations and is from a domain leading peer-reviewed journal.

  8. (barth2023nucleasegenesoccupy pages 18-20): Zachary K Barth, Drew T Dunham, and Kimberley D Seed. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv, Mar 2023. URL: https://doi.org/10.1101/2023.03.23.533998, doi:10.1101/2023.03.23.533998. This article has 20 citations.

  9. (barth2023nucleasegenesoccupy pages 10-12): Zachary K Barth, Drew T Dunham, and Kimberley D Seed. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv, Mar 2023. URL: https://doi.org/10.1101/2023.03.23.533998, doi:10.1101/2023.03.23.533998. This article has 20 citations.

  10. (barth2023nucleasegenesoccupy pages 15-18): Zachary K Barth, Drew T Dunham, and Kimberley D Seed. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv, Mar 2023. URL: https://doi.org/10.1101/2023.03.23.533998, doi:10.1101/2023.03.23.533998. This article has 20 citations.

  11. (barth2021achimericnuclease pages 4-5): Zachary K Barth, Maria HT Nguyen, and Kimberley D Seed. A chimeric nuclease substitutes a phage crispr-cas system to provide sequence-specific immunity against subviral parasites. eLife, Jul 2021. URL: https://doi.org/10.7554/elife.68339, doi:10.7554/elife.68339. This article has 46 citations and is from a domain leading peer-reviewed journal.

  12. (barth2021achimericnuclease pages 2-4): Zachary K Barth, Maria HT Nguyen, and Kimberley D Seed. A chimeric nuclease substitutes a phage crispr-cas system to provide sequence-specific immunity against subviral parasites. eLife, Jul 2021. URL: https://doi.org/10.7554/elife.68339, doi:10.7554/elife.68339. This article has 46 citations and is from a domain leading peer-reviewed journal.

  13. (barth2021achimericnuclease pages 7-9): Zachary K Barth, Maria HT Nguyen, and Kimberley D Seed. A chimeric nuclease substitutes a phage crispr-cas system to provide sequence-specific immunity against subviral parasites. eLife, Jul 2021. URL: https://doi.org/10.7554/elife.68339, doi:10.7554/elife.68339. This article has 46 citations and is from a domain leading peer-reviewed journal.

  14. (netter2021aphagesatellite pages 11-13): Zoe Netter, Caroline M. Boyd, Tania V. Silvas, and Kimberley D. Seed. A phage satellite tunes inducing phage gene expression using a domesticated endonuclease to balance inhibition and virion hijacking. Nucleic Acids Research, 49:4386-4401, Nov 2021. URL: https://doi.org/10.1101/2020.11.28.402263, doi:10.1101/2020.11.28.402263. This article has 35 citations and is from a highest quality peer-reviewed journal.

  15. (netter2021aphagesatellite pages 13-15): Zoe Netter, Caroline M. Boyd, Tania V. Silvas, and Kimberley D. Seed. A phage satellite tunes inducing phage gene expression using a domesticated endonuclease to balance inhibition and virion hijacking. Nucleic Acids Research, 49:4386-4401, Nov 2021. URL: https://doi.org/10.1101/2020.11.28.402263, doi:10.1101/2020.11.28.402263. This article has 35 citations and is from a highest quality peer-reviewed journal.

  16. (netter2021aphagesatellite pages 15-16): Zoe Netter, Caroline M. Boyd, Tania V. Silvas, and Kimberley D. Seed. A phage satellite tunes inducing phage gene expression using a domesticated endonuclease to balance inhibition and virion hijacking. Nucleic Acids Research, 49:4386-4401, Nov 2021. URL: https://doi.org/10.1101/2020.11.28.402263, doi:10.1101/2020.11.28.402263. This article has 35 citations and is from a highest quality peer-reviewed journal.

  17. (barth2024genomicanalysisof pages 10-11): Zachary K Barth, Ian Hicklin, Julien ThΓ©zΓ©, Jun Takatsuka, Madoka Nakai, Elisabeth A Herniou, Anne M Brown, and Frank O Aylward. Genomic analysis of hyperparasitic viruses associated with entomopoxviruses. Virus Evolution, Jul 2024. URL: https://doi.org/10.1093/ve/veae051, doi:10.1093/ve/veae051. This article has 6 citations and is from a peer-reviewed journal.

  18. (barth2023nucleasegenesoccupy pages 23-25): Zachary K Barth, Drew T Dunham, and Kimberley D Seed. Nuclease genes occupy boundaries of genetic exchange between bacteriophages. bioRxiv, Mar 2023. URL: https://doi.org/10.1101/2023.03.23.533998, doi:10.1101/2023.03.23.533998. This article has 20 citations.

Citations

  1. barth2023nucleasegenesoccupy pages 3-4
  2. barth2024genomicanalysisof pages 8-10
  3. barth2023nucleasegenesoccupy pages 4-6
  4. barth2021achimericnuclease pages 7-9
  5. barth2021achimericnuclease pages 12-14
  6. netter2021aphagesatellite pages 11-13
  7. barth2023nucleasegenesoccupy pages 10-12
  8. barth2023nucleasegenesoccupy pages 15-18
  9. barth2024genomicanalysisof pages 10-11
  10. barth2023nucleasegenesoccupy pages 6-10
  11. barth2023nucleasegenesoccupy pages 18-20
  12. barth2021achimericnuclease pages 4-5
  13. barth2021achimericnuclease pages 2-4
  14. netter2021aphagesatellite pages 13-15
  15. netter2021aphagesatellite pages 15-16
  16. barth2023nucleasegenesoccupy pages 23-25
  17. https://doi.org/10.1101/2023.03.23.533998;
  18. https://doi.org/10.1093/ve/veae051;
  19. https://doi.org/10.7554/elife.68339
  20. https://doi.org/10.1101/2020.11.28.402263
  21. https://doi.org/10.1101/2023.03.23.533998
  22. https://doi.org/10.1093/ve/veae051
  23. https://doi.org/10.1101/2023.03.23.533998,
  24. https://doi.org/10.1093/ve/veae051,
  25. https://doi.org/10.7554/elife.68339,
  26. https://doi.org/10.1101/2020.11.28.402263,

πŸ“š Additional Documentation

Notes

(SNIPE-notes.md)

SNIPE Gene Notes

Key Paper: Saxton et al. (2026) Nature

Title: A membrane-bound nuclease directly cleaves phage DNA during genome injection
Authors: Saxton DS, DeWeirdt PC, Doering CR, Roney IJ & Laub MT
DOI: 10.1038/s41586-026-10207-1
PMID: 41741653

Identification

  • Originally identified as PD-lambda-1 in a functional genetic screen for anti-phage defence systems in the E. coli pangenome PMID:36123438
  • Renamed SNIPE: Surface-associated Nuclease Inhibiting Phage Entry PMID:41741653
  • Found in wild E. coli strains (ECOR collection, strain MOD1-ECOR26); NOT present in K-12 MG1655
  • UniProt: A0A8T9CRB7 (TrEMBL, ECOLX; from strain T0181B.E-10, same RefSeq WP_001606968.1)

Protein Architecture (500 aa)

Three domains confirmed by AlphaFold, HHpred, and DeepTMHMM:

  1. N-terminal transmembrane domain (aa 5-24): single-pass TM helix anchoring to inner membrane. N-terminus is periplasmic, rest of protein is cytoplasmic PMID:41741653
  2. DUF4041 domain (aa 144-262, now IPR025280/PF13250 "SNIPE associated domain"): positively charged surface facilitates DNA binding; also interacts with phage tape measure proteins (TMPs) PMID:41741653
  3. GIY-YIG nuclease domain (aa 357-450): catalytic DNA endonuclease; E414 is catalytic residue PMID:41741653

Mechanism of Action

SNIPE provides direct defence (infected cell survives), distinct from abortive infection:

  • SNIPE pre-associates with ManYZ (mannose permease) in the inner membrane BEFORE infection PMID:41741653
  • During phage genome injection through ManYZ, DUF4041 domain binds the phage tape measure protein (TMP), positioning the nuclease to cleave incoming DNA PMID:41741653
  • 32P-labelled phage DNA is cleaved from ~42,000 bp down to <100 bp fragments during injection PMID:41741653
  • SNIPE does NOT affect phage adsorption PMID:41741653
  • SNIPE does NOT target pre-existing phage genomes (lysogens) PMID:41741653
  • SNIPE does NOT block plasmid DNA transformation PMID:41741653

Auto-inhibition

  • Membrane-localized SNIPE does NOT cleave host DNA PMID:41741653
  • SNIPE(deltaTM) localizes to nucleoid and IS toxic β€” cleaves host DNA PMID:41741653
  • The TM domain prevents autoimmunity by anchoring SNIPE away from chromosomal DNA

ManYZ Interaction

  • ManYZ = mannose permease inner membrane complex, required for lambda genome injection
  • SNIPE pre-associates with ManYZ (TurboID proximity labelling) PMID:41741653
  • Robust defence requires ManYZ against lambda and related phages
  • ManYZ-independent defence: SNIPE provides moderate defence against siphoviruses independently of ManYZ PMID:41741653

TMP Interaction

  • DUF4041 interacts with phage tape measure proteins physically PMID:41741653
  • UV crosslinking + mass spec confirms SNIPE-TMP direct contact via pBPA at residue N250 (adjacent to W257R mutation site) PMID:41741653
  • SNIPE gain-of-function mutations (L253H, E264K, K305N; E223K, T319A; W257R, I308V) enhance binding to Bas14 TMP PMID:41741653
  • Phage escape mutations map exclusively to TMP gene PMID:41741653

Evolutionary Diversity

  • ~500 curated SNIPE homologues across many bacterial phyla PMID:41741653
  • 33% of well-sequenced bacterial clades harbour at least one SNIPE homologue [PMID:36123438, PMID:41741653]
  • GIY-YIG nuclease domain: most conserved region
  • DUF4041: moderate conservation, positively charged DNA-binding interface conserved
  • N-terminal region: highest variability β€” functions as adapter for phage specificity
  • 59% have 1 TM domain
  • 7% have 2 TM domains
  • 34% lack TM domains β€” use alternative membrane-targeting strategies:
    • DivIVA domains (negative membrane curvature binding)
    • Type III secretion system domains
    • Pleckstrin homology domains (phospholipid binding)
    • Phage tail protein fusions PMID:41741653

Self/Non-Self Discrimination

SNIPE represents a novel strategy distinct from:
- CRISPR-Cas: sequence-specific recognition via guide RNAs
- Restriction-modification: recognition of DNA methylation marks
- SNIPE: exploits spatial organization β€” phage DNA must pass through the membrane during injection, and SNIPE is positioned there to intercept it PMID:41741653

Comparison to Other Systems

  • Zorya: also localizes to membrane at genome injection sites, but senses perturbations rather than directly cleaving DNA [PMID:41741653 ref 34,35]
  • Kiwa: membrane-embedded defence supercomplex at phage attachment sites [PMID:41741653 ref 37]
  • IFITM proteins (eukaryotic): block viral membrane fusion β€” conceptual parallel [PMID:41741653 ref 38,39]

Key References

  1. PMID:41741653 - Saxton et al. 2026, Nature. SNIPE characterization.
  2. PMID:36123438 - Vassallo et al. 2022, Nat Microbiol. Original identification as PD-lambda-1.
  3. PMID:37460672 - Georjon & Bernheim 2023, Cell Host Microbe. Systematic exploration of E. coli phage-host interactions (BASEL collection).
  4. PMID:31857715 - Makarova et al. 2020. Classification of CRISPR-Cas systems.
  5. PMID:36880887 - Branon et al. 2018, Nat Biotechnol. TurboID proximity labelling.

Bioinformatics Results

(RESULTS.md)

SNIPE Architecture-Aware Feature Analysis (InterPro)

Question

Suggest data-driven feature combinations for:

IPR025280 + GIY-YIG nuclease + membrane targeting features

to support an architecture-aware annotation strategy.

Runs

  • Primary run: IPR025280 (SNIPE associated domain)
  • Secondary validation run: IPR029330 (small control run to test script on a different input)

Output folders:

  • results/IPR025280/
  • results/IPR029330/

Key Results for IPR025280

Architecture prevalence

Top architectures from results/IPR025280/architecture_table.tsv:

  1. PF13250:IPR025280-PF13455 -> 1109 proteins (68.80%)
  2. PF13250:IPR025280-PF10544:IPR018306 -> 270 proteins (16.75%)
  3. PF13250:IPR025280 -> 139 proteins (8.62%)

Top 3 cover 1518/1612 proteins (94.17%).

Catalytic partner (GIY-YIG-like proxy) co-features

From results/IPR025280/cooccurring_domain_weighted.tsv:

  • PF13455 -> 1189 proteins (73.76%)
  • PF10544 + IPR018306 -> 277 proteins (17.18%)

Combined, these catalytic co-features cover 1466/1612 proteins (90.94%).

Membrane-targeting signals

From results/IPR025280/nterm_tm_heuristic_overall.tsv:

  • N-terminal TM-like heuristic (first 70 aa): 990/1612 proteins (61.41%)

From results/IPR025280/representative_extra_features.tsv:

  • Dominant representative Q7MG17: TMhelix 5-22, signal peptide 1-23
  • Second representative Q6AMX9: TMhelix 7-24

Rare but explicit membrane-associated accessory domains (from cooccurring_domain_weighted.tsv):

  • PF14470 / IPR039519 (bacterial PH domain): 3 proteins (0.19%)
  • PF05154 / IPR007829 (TM2 domain): 1 protein (0.06%)

Potentially membrane-linked but weaker evidence:

  • PF10708 / IPR018929 (DUF2510): 76 proteins (4.71%); Pfam description notes many members are putative membrane proteins.

Suggested Feature Sets for Rule Design

Tier 1 (high-confidence)

Use all of:

  1. IPR025280 (SNIPE associated domain)
  2. Catalytic partner: PF13455 OR IPR018306/PF10544
  3. At least one membrane-targeting signal:
  4. N-terminal TMhelix/signal peptide (or equivalent N-term TM-like predictor), OR
  5. membrane-associated domain such as IPR007829 or IPR039519 when present

Tier 2 (exploratory / broader)

Use:

  1. IPR025280
  2. Catalytic partner: PF13455 OR IPR018306/PF10544
  3. Optional membrane-linked accessory: IPR018929 (DUF2510)

with lower confidence due weaker direct membrane evidence.

Suggested architecture-aware implementation note:

IPR025280 + (PF13455 OR IPR018306/PF10544) + (N-term TM/signal peptide OR membrane-associated accessory domain such as IPR007829/IPR039519; optional lower-confidence IPR018929).

Checklist

  • [x] None of the scripts use hardcoded inputs or outputs
  • [x] Scripts tested on at least one other input (IPR029330)
  • [x] Analyses completed as expected for the primary target (IPR025280)
  • [x] Direct script outputs are present in the analysis folder
  • [x] Summary includes provenance and quantitative justification

πŸ“„ View Raw YAML

 
id: A0A8T9CRB7
gene_symbol: SNIPE
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:562
  label: Escherichia coli
description: >-
  SNIPE (Surface-associated Nuclease Inhibiting Phage Entry) is a 500 amino acid inner
  membrane-bound
  GIY-YIG family DNA endonuclease that provides direct anti-bacteriophage defence
  in Escherichia coli.
  SNIPE constitutively localizes to the inner membrane via an N-terminal single-pass
  transmembrane helix
  (aa 5-24) and pre-associates with the ManYZ mannose permease complex before phage
  infection. During
  phage genome injection, the central DUF4041 domain (aa 144-262, now designated the
  SNIPE-associated
  domain, IPR025280) binds both incoming phage DNA and the phage tape measure protein
  (TMP), positioning
  the C-terminal GIY-YIG nuclease domain (aa 357-450, catalytic residue E414) to cleave
  phage DNA as it
  crosses the inner membrane. This provides direct defence β€” the infected cell survives
  β€” in contrast
  to abortive infection systems. SNIPE does not affect phage adsorption, does not
  target pre-existing
  intracellular phage genomes (lysogens), and does not block plasmid transformation,
  indicating its
  activity is specific to the phage genome injection process. Originally identified
  as PD-lambda-1 in
  a functional screen of 71 diverse E. coli pangenomes (PMID:36123438), SNIPE homologues
  (~500 curated)
  are found across many bacterial phyla, with 33% of well-sequenced clades harbouring
  at least one
  homologue. The N-terminal region is highly variable and functions as a phage-specificity
  adapter, with
  59% of homologues having one TM domain, 7% having two, and 34% using alternative
  membrane-targeting
  strategies (DivIVA domains, type III secretion domains, PH domains). SNIPE represents
  a previously
  unknown self/non-self discrimination strategy based on subcellular localization
  rather than sequence
  recognition (CRISPR-Cas) or modification detection (restriction-modification).
  Note: UniProt entry A0A8T9CRB7 is from E. coli strain T0181B.E-10. The experimentally
  characterized
  SNIPE was from strain MOD1-ECOR26 (GenBank RCP76574.1, locus APT27_20780). Both
  share RefSeq
  WP_001606968.1. SNIPE is not present in E. coli K-12 MG1655.
tags:
- anti-phage defence
- nuclease
- membrane protein
- innate immunity
- phage-host interaction
references:
- id: PMID:41741653
  title: A membrane-bound nuclease directly cleaves phage DNA during genome injection
  findings:
  - statement: >-
      SNIPE is a membrane-bound nuclease that directly cleaves phage DNA during
      genome
      injection, providing direct defence against bacteriophage
    supporting_text: >-
      we demonstrate that SNIPE directly cleaves phage DNA during genome injection
  - statement: >-
      SNIPE constitutively localizes to the bacterial cell membrane
    supporting_text: >-
      we characterize SNIPE, an anti-bacteriophage defence system that constitutively
      localizes to the bacterial cell membrane in Escherichia coli to block phage
  - statement: >-
      SNIPE pre-associates with host proteins for lambda genome entry and with
      the tape
      measure protein during genome injection
    supporting_text: >-
      SNIPE associates with host proteins essential for Ξ» genome entry and with
      the Ξ»
      tape measure protein, which facilitates Ξ» genome injection across the inner
      membrane
  - statement: >-
      Radiolabelled phage DNA tracking demonstrates SNIPE cleaves DNA during injection
    supporting_text: >-
      Using radiolabelled phage DNA and time-lapse microscopy to track phage genomes,
      we
      demonstrate that SNIPE directly cleaves phage DNA during genome injection
  - statement: >-
      SNIPE provides ManYZ-independent defence against siphoviruses via direct
      TMP interaction
    supporting_text: >-
      SNIPE also defends against diverse siphoviruses, probably through direct
      interactions
      with their tape measure proteins
  - statement: >-
      SNIPE is a widespread defence system representing a novel self/non-self
      discrimination strategy
    supporting_text: >-
      SNIPE as a widespread bacterial defence system that exploits the spatial
      organization of
      phage genome injection to specifically target viral DNA, representing a
      previously unknown
      strategy for distinguishing self from non-self in prokaryotic immune systems
- id: PMID:36123438
  title: >-
    A functional selection reveals previously undetected anti-phage defence systems
    in the
    E. coli pangenome
  findings:
  - statement: >-
      SNIPE (originally PD-lambda-1) was identified in a functional metagenomic
      screen of 71
      diverse E. coli strains as a novel anti-phage defence system
    supporting_text: >-
      Our results unveil 21 conserved defence systems, none of which were previously
      detected
      as enriched in defence islands
  - statement: >-
      SNIPE is a membrane-anchored protein with DUF4041 and a GIY-YIG nuclease
      domain
    supporting_text: >-
      a putative membrane-anchored protein with a central coiled-coil domain (DUF4041)
      and a C-terminal DNA binding/cleavage domain
  - statement: >-
      Defence systems including SNIPE are carried primarily by prophages and mobile
      genetic elements
    supporting_text: >-
      intact prophages and mobile genetic elements are primary reservoirs and
      distributors
      of defence systems in E. coli
- id: file:ECOLX/SNIPE/SNIPE-deep-research-falcon.md
  title: Deep research on SNIPE/DUF4041 domain-containing protein (falcon)
  findings:
  - statement: >-
      T5orf172/MUG113 (PF13455) is a GIY-YIG endonuclease subfamily; MUG113 profile
      is
      highly related to T5orf172, placing SNIPE's nuclease domain in the GIY-YIG
      HEG space
    supporting_text: >-
      T5orf172 is a subfamily of GIY-YIG endonucleases ... the two profiles [T5orf172
      and MUG113] are highly related
  - statement: >-
      T5orf172-family proteins have modular architecture with variable DNA-binding
      modules
      determining target specificity, paired with a conserved nuclease domain
    supporting_text: >-
      a nuclease domain paired with variable DNA-binding modules that determine
      target
      specificity
existing_annotations:
  # No existing GO annotations for A0A8T9CRB7 β€” all annotations below are NEW proposals

  # === Molecular Function ===
- term:
    id: GO:0004520
    label: DNA endonuclease activity
  evidence_type: IDA
  original_reference_id: PMID:41741653
  review:
    summary: >-
      SNIPE contains a C-terminal GIY-YIG nuclease domain (aa 357-450) that endonucleolytically
      cleaves phage DNA during genome injection. Substitution of the predicted catalytic
      residue
      E414 to alanine abolishes both nuclease activity and phage defence (PMID:41741653).
      Radiolabelled 32P phage DNA is degraded from ~42 kb to fragments <100 bp and
      mononucleotides in SNIPE-expressing cells, dependent on E414 (PMID:41741653).
      The
      pattern of degradation (smear of fragments rather than defined products) is
      consistent
      with endonucleolytic cleavage, though in vitro reconstitution has not yet
      been performed.
      The GIY-YIG nuclease domain is the most conserved region across ~500 SNIPE
      homologues
      (PMID:41741653), and domain-level homology to the T5orf172/MUG113 family of
      GIY-YIG
      endonucleases is confirmed by InterPro/Pfam assignments (IPR018306, PF13455).
      GO:0004520
      is the appropriate level of specificity; there is no GIY-YIG-specific child
      term in GO,
      and the data do not support a more specific term like GO:0015666 (restriction
      endodeoxyribonuclease activity) since SNIPE does not recognize specific DNA
      sequences
      or modification states.
    action: NEW
    reason: >-
      Core molecular function of SNIPE, directly demonstrated by multiple experimental
      approaches in PMID:41741653: (1) 32P-labelled phage DNA cleavage assay showing
      degradation during injection, (2) E414A catalytic dead mutant abolishing cleavage
      and defence, (3) Gam-GFP double-strand break reporter showing SNIPE-dependent
      foci,
      (4) CFP-ParB foci reduced ~30-fold indicating DNA degradation during injection.
      The domain architecture (GIY-YIG nuclease, IPR018306/PF13455) independently
      supports
      endonuclease activity via homology to biochemically characterized family members.
      IDA evidence code is appropriate because the nuclease activity was directly
      assayed
      in vivo using radiolabelled substrate and catalytic mutant controls.
    supported_by:
    - reference_id: PMID:41741653
      supporting_text: >-
        we demonstrate that SNIPE directly cleaves phage DNA during genome injection
    - reference_id: PMID:41741653
      supporting_text: >-
        Using radiolabelled phage DNA and time-lapse microscopy to track phage genomes,
        we demonstrate that SNIPE directly cleaves phage DNA during genome injection
    - reference_id: PMID:36123438
      supporting_text: >-
        a putative membrane-anchored protein with a central coiled-coil domain
        (DUF4041)
        and a C-terminal DNA binding/cleavage domain
    - reference_id: file:ECOLX/SNIPE/SNIPE-deep-research-falcon.md
      supporting_text: >-
        T5orf172 is a subfamily of GIY-YIG endonucleases ... the two profiles
        [T5orf172
        and MUG113] are highly related
- term:
    id: GO:0003690
    label: double-stranded DNA binding
  evidence_type: IDA
  original_reference_id: PMID:41741653
  review:
    summary: >-
      The DUF4041/SNIPE-associated domain (aa 144-262) of SNIPE has a positively
      charged
      surface that facilitates DNA binding. When the TM domain is removed
      (SNIPE(deltaTM E414A)-GFP), the protein co-localizes with the DAPI-stained
      nucleoid
      (Pearson R=0.76), and this co-localization is abolished when DUF4041 is also
      deleted
      (deltaDUF4041 shows R=0.13) (PMID:41741653). A DUF4041-only fusion to GFP
      also
      localizes to the nucleoid. ConSurf analysis shows the positively charged DNA-binding
      interface is conserved across SNIPE homologues (PMID:41741653). Note that
      the evidence
      for DNA binding is based on fluorescence microscopy co-localization with the
      nucleoid
      rather than a direct biochemical binding assay (e.g. EMSA); however, the domain-dependent
      co-localization pattern and the conserved positively charged surface provide
      strong
      support for direct DNA binding. Phage lambda DNA is dsDNA, making GO:0003690
      the
      appropriate specific term. The original identification also noted the C-terminal
      region
      as a "DNA binding/cleavage domain" (PMID:36123438).
    action: NEW
    reason: >-
      DNA binding by DUF4041 is demonstrated by microscopy showing domain-dependent
      nucleoid
      co-localization (PMID:41741653): removal of DUF4041 abolishes nucleoid association.
      This is further supported by the conserved positively charged surface identified
      by
      ConSurf analysis across ~500 homologues, and by domain annotation as a DNA-binding
      domain (IPR018306 Phage_T5_Orf172_DNA-bd). IDA evidence code is appropriate
      for
      microscopy-based localization experiments with domain deletion controls. The
      term
      GO:0003690 (double-stranded DNA binding) is preferred over GO:0003677 (DNA
      binding)
      because phage lambda DNA is dsDNA and the nucleoid is dsDNA.
    supported_by:
    - reference_id: PMID:36123438
      supporting_text: >-
        a putative membrane-anchored protein with a central coiled-coil domain
        (DUF4041)
        and a C-terminal DNA binding/cleavage domain

  # === Biological Process ===
- term:
    id: GO:0051607
    label: defense response to virus
  evidence_type: IDA
  original_reference_id: PMID:41741653
  review:
    summary: >-
      SNIPE provides direct defence against bacteriophage lambda and diverse siphoviruses.
      SNIPE-expressing cells survive phage lambda infection at high MOI where control
      cells
      lyse (PMID:41741653). Defence is demonstrated by: time-lapse microscopy showing
      cell
      survival, growth curves at MOI 0.1-10, plaque assays showing 6-7 log reduction
      in
      phage titre, and the BASEL collection screen showing protection against diverse
      siphoviruses (both ManYZ-dependent and ManYZ-independent) (PMID:41741653).
      SNIPE
      provides direct defence (cell survival) rather than abortive infection. It
      was
      originally identified as one of 21 novel defence systems in a functional metagenomic
      screen of the E. coli pangenome (PMID:36123438).
    action: NEW
    reason: >-
      Defence against bacteriophage is the primary evolved biological function of
      SNIPE,
      supported by multiple complementary experimental approaches (PMID:41741653)
      and by
      its original identification via a functional anti-phage defence screen (PMID:36123438).
      GO:0051607 (defense response to virus) is the most specific existing BP term.
      There
      is currently no GO term for "defense response to bacteriophage" specifically;
      a new
      term request has been drafted (see projects/SNIPE/go-issue-antiviral-nucleic-acid-defense.md).
      IDA evidence code is appropriate as defence was directly assayed by growth
      curves,
      plaque assays, and single-cell microscopy.
    supported_by:
    - reference_id: PMID:41741653
      supporting_text: >-
        we characterize SNIPE, an anti-bacteriophage defence system that constitutively
        localizes to the bacterial cell membrane in Escherichia coli to block
        phage
    - reference_id: PMID:41741653
      supporting_text: >-
        SNIPE as a widespread bacterial defence system that exploits the spatial
        organization
        of phage genome injection to specifically target viral DNA, representing
        a previously
        unknown strategy for distinguishing self from non-self in prokaryotic
        immune systems
    - reference_id: PMID:36123438
      supporting_text: >-
        Our results unveil 21 conserved defence systems, none of which were previously
        detected as enriched in defence islands
- term:
    id: GO:0045071
    label: negative regulation of viral genome replication
  evidence_type: IDA
  original_reference_id: PMID:41741653
  review:
    summary: >-
      SNIPE prevents phage genome replication by destroying the phage DNA during
      the injection
      process, before the genome enters the cytoplasm intact. CFP-ParB foci (a proxy
      for
      phage genome establishment) are reduced ~30-fold in SNIPE-expressing cells
      (PMID:41741653). Phage produced per cell is not significantly different between
      SNIPE
      and empty vector when inducing lysogens, confirming that SNIPE targets the
      injection
      step specifically and does not affect pre-existing intracellular phage genomes
      (PMID:41741653). While the net effect is prevention of viral genome replication,
      the
      mechanism is more precisely described as destruction of the phage genome during
      membrane translocation rather than regulation of replication per se. GO:0046597
      (host-mediated suppression of symbiont invasion) may be a more mechanistically
      precise
      BP term since SNIPE blocks the entry/establishment of the phage genome rather
      than
      regulating its replication after entry.
    action: NEW
    reason: >-
      The outcome of SNIPE activity is that viral genome replication is completely
      prevented,
      making GO:0045071 a defensible annotation. The evidence is strong: CFP-ParB
      foci
      reduction demonstrates that phage genomes do not establish in SNIPE-expressing
      cells
      (PMID:41741653). However, SNIPE acts upstream of replication -- it destroys
      the DNA
      during injection, not by regulating the replication machinery. This distinction
      may
      matter for precision. The annotation is retained because the net biological
      outcome
      (no viral genome replication) is accurately captured. See also the additional
      GO:0046597 annotation below for a more mechanistically precise complementary
      term.
      IDA evidence code is appropriate.
    supported_by:
    - reference_id: PMID:41741653
      supporting_text: >-
        we demonstrate that SNIPE directly cleaves phage DNA during genome injection
    - reference_id: PMID:41741653
      supporting_text: >-
        SNIPE associates with host proteins essential for lambda genome entry
        and with the
        lambda tape measure protein, which facilitates lambda genome injection
        across the
        inner membrane
- term:
    id: GO:0046597
    label: host-mediated suppression of symbiont invasion
  evidence_type: IDA
  original_reference_id: PMID:41741653
  review:
    summary: >-
      SNIPE inhibits phage genome entry into the bacterial cell by cleaving phage
      DNA
      during the injection process at the inner membrane. This directly suppresses
      the
      phage's invasion of the host cell. GO:0046597 is defined as "a process in
      which a
      host inhibits or disrupts the entry of a symbiont into a host cell." While
      bacteriophages inject their genome rather than entering bodily, the phage
      genome
      translocation across the inner membrane constitutes the functional "entry"
      event that
      SNIPE suppresses. SNIPE does not block phage adsorption to the cell surface
      -- phage
      adsorption is unaffected (PMID:41741653) -- but it destroys the phage DNA
      during
      membrane translocation, preventing genome establishment. This term complements
      GO:0045071 by providing a more mechanistically precise description of SNIPE's
      biological role.
    action: NEW
    reason: >-
      SNIPE acts specifically at the step of phage genome injection across the inner
      membrane (PMID:41741653). It does not affect phage adsorption, does not target
      pre-existing lysogens, and does not block plasmid transformation -- it is
      specific
      to the injection process. GO:0046597 (host-mediated suppression of symbiont
      invasion)
      captures this specificity better than GO:0045071 (negative regulation of viral
      genome
      replication), which implies action on the replication process itself. GO:0046597
      is
      the parent of several relevant child terms in GO and is compatible with bacterial
      hosts defending against phage. IDA evidence code is appropriate.
    supported_by:
    - reference_id: PMID:41741653
      supporting_text: >-
        we characterize SNIPE, an anti-bacteriophage defence system that constitutively
        localizes to the bacterial cell membrane in Escherichia coli to block
        phage
    - reference_id: PMID:36123438
      supporting_text: >-
        We confirmed that each system did not affect phage adsorption (Extended Data
        Fig
- term:
    id: GO:0006308
    label: DNA catabolic process
  evidence_type: IDA
  original_reference_id: PMID:41741653
  review:
    summary: >-
      SNIPE degrades phage DNA from ~42 kb to fragments less than 100 bp and mononucleotides
      during genome injection (PMID:41741653). This is a DNA catabolic process --
      the
      breakdown of DNA. The 32P-labelled DNA tracking experiment directly demonstrates
      catabolism of the phage DNA substrate. While the MF annotation (GO:0004520
      DNA
      endonuclease activity) captures the catalytic mechanism, GO:0006308 captures
      the
      biological process of DNA degradation that results from this activity.
    action: NEW
    reason: >-
      The degradation of phage DNA from intact genomic molecules (~42 kb) to small
      fragments
      (<100 bp) and mononucleotides is directly demonstrated by the 32P-labelled
      DNA
      cleavage assay (PMID:41741653). This constitutes DNA catabolism. GO:0006308
      provides
      a process-level annotation that complements the molecular function (GO:0004520)
      and
      the higher-level biological context (GO:0051607 defense response to virus).
      IDA
      evidence code is appropriate as the catabolic activity was directly measured
      using
      radiolabelled substrate.
    supported_by:
    - reference_id: PMID:41741653
      supporting_text: >-
        we demonstrate that SNIPE directly cleaves phage DNA during genome injection

  # === Cellular Component ===
- term:
    id: GO:0005887
    label: integral component of plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:41741653
  review:
    summary: >-
      SNIPE is an integral inner membrane protein with a single-pass TM helix (aa
      5-24).
      Topology was confirmed by PhoA-LacZalpha fusion analysis: PhoA was active
      only when
      inserted at the N-terminus (periplasmic side), and LacZalpha was active only
      when
      inserted downstream of the TM domain (cytoplasmic side) (PMID:41741653). SNIPE-GFP
      localizes uniformly to the cell membrane by fluorescence microscopy (PMID:41741653).
      Immunoblotting of fractionated cell lysates shows SNIPE is strongly enriched
      in the
      membrane fraction (PMID:41741653). DeepTMHMM and Phobius both predict a transmembrane
      helix at residues 6-24, consistent with the UniProt annotation (ECO:0000256|SAM:Phobius).
      In bacteria, GO:0005886 (plasma membrane) corresponds to the inner/cytoplasmic
      membrane. The single-pass TM helix makes SNIPE an integral (not peripheral)
      component,
      supporting GO:0005887 over GO:0005886.
    action: NEW
    reason: >-
      Integral membrane localization is directly demonstrated by three independent
      experimental approaches in PMID:41741653: (1) PhoA/LacZalpha topology mapping
      confirming transmembrane orientation, (2) fluorescence microscopy of SNIPE-GFP
      showing
      uniform membrane localization, (3) membrane fractionation/immunoblotting showing
      enrichment in membrane fraction. This is further supported by the predicted
      TM helix
      (Phobius, DeepTMHMM) in the UniProt record. GO:0005887 (integral component
      of plasma
      membrane) is preferred over GO:0005886 (plasma membrane) because the single-pass
      TM
      helix makes SNIPE an integral membrane protein. IDA evidence code is appropriate
      for
      the topology mapping and fractionation experiments.
    supported_by:
    - reference_id: PMID:41741653
      supporting_text: >-
        an anti-bacteriophage defence system that constitutively localizes to
        the bacterial
        cell membrane in Escherichia coli
    - reference_id: PMID:41741653
      supporting_text: >-
        Here, we characterize SNIPE, an anti-bacteriophage defence system that constitutively
        localizes to the bacterial cell membrane in Escherichia coli to block phage
        Ξ» infection
core_functions:
- description: >-
    SNIPE is a membrane-anchored DNA endonuclease that directly cleaves bacteriophage
    DNA
    during the genome injection process. It exploits the spatial organization of
    phage genome
    entry β€” the fact that phage DNA must cross the inner membrane β€” to distinguish
    foreign
    (viral) DNA from self (chromosomal) DNA. The GIY-YIG nuclease domain provides
    the catalytic
    endonuclease activity, with E414 as the essential catalytic residue. The DUF4041
    domain
    binds both phage DNA (via a conserved positively charged interface) and phage
    tape measure
    proteins (TMPs), positioning the nuclease at the site of genome injection. The
    N-terminal
    TM domain anchors SNIPE to the inner membrane, preventing autoimmune cleavage
    of host
    chromosomal DNA. SNIPE pre-associates with the ManYZ mannose permease complex,
    which is
    the inner membrane conduit for lambda genome injection, ensuring SNIPE is positioned
    at
    genome entry sites before infection occurs. This provides direct defence β€” the
    infected
    cell survives β€” in contrast to abortive infection systems that sacrifice the
    infected cell.
    SNIPE also provides ManYZ-independent defence against diverse siphoviruses,
    probably through
    direct interactions with their TMPs via the DUF4041 domain. The ~500 SNIPE homologues
    across
    bacterial phyla show conservation of the GIY-YIG nuclease and DUF4041 domains,
    while the
    N-terminal region is highly diversified and functions as a phage-specificity
    adapter with
    varied membrane-targeting strategies (TM helices, DivIVA domains, T3SS domains,
    PH domains).
  molecular_function:
    id: GO:0004520
    label: DNA endonuclease activity
  directly_involved_in:
  - id: GO:0051607
    label: defense response to virus
  - id: GO:0045071
    label: negative regulation of viral genome replication
  locations:
  - id: GO:0005886
    label: plasma membrane
  supported_by:
  - reference_id: PMID:41741653
    supporting_text: >-
      SNIPE as a widespread bacterial defence system that exploits the spatial
      organization
      of phage genome injection to specifically target viral DNA, representing
      a previously
      unknown strategy for distinguishing self from non-self in prokaryotic immune
      systems
  - reference_id: PMID:36123438
    supporting_text: >-
      A functional selection reveals previously undetected anti-phage defence
      systems in
      the E. coli pangenome
proposed_new_terms:
- proposed_name: SNIPE defense system
  proposed_definition: >-
    A defense response to a virus in which a membrane-anchored nuclease of the SNIPE
    family cleaves viral DNA during genome injection across the cell membrane. SNIPE
    proteins associate with inner membrane components at phage genome injection
    sites,
    bind phage tape measure proteins via their DUF4041 domain, and use a GIY-YIG
    nuclease
    domain to degrade incoming phage DNA before it enters the cytoplasm. Unlike
    restriction-modification or CRISPR-Cas systems, self/non-self discrimination
    is
    achieved through subcellular localization at the membrane rather than recognition
    of
    specific DNA sequences or modifications.
  justification: >-
    The current anti-foreign nucleic acid branch (GO:0099046 clearance of foreign
    intracellular nucleic acids) does not capture SNIPE mechanism, because SNIPE
    cleaves
    phage DNA during translocation at the membrane before the DNA becomes intracellular.
    A dedicated term under GO:0051607 (defense response to virus) is needed to represent
    this direct anti-phage mechanism.
  proposed_parent:
    id: GO:0051607
    label: defense response to virus
  supported_by:
  - reference_id: PMID:41741653
    supporting_text: >-
      we demonstrate that SNIPE directly cleaves phage DNA during genome injection
  - reference_id: PMID:36123438
    supporting_text: >-
      A functional selection reveals previously undetected anti-phage defence
      systems
      in the E. coli pangenome
- proposed_name: antiviral defense by targeting viral nucleic acid
  proposed_definition: >-
    A defense response to a virus in which the host targets viral nucleic acid for
    degradation or modification, preventing viral replication. Includes systems
    that act
    on nucleic acid after cell entry (e.g. CRISPR-Cas, restriction-modification)
    and
    systems that act during genome injection (e.g. SNIPE).
  justification: >-
    Optional intermediate grouping term matching the GO issue proposal. This would
    provide
    a clean parent for nucleic acid-targeting anti-viral systems such as CRISPR-Cas,
    restriction-modification, and SNIPE while preserving mechanistic distinctions
    in child terms.
  proposed_parent:
    id: GO:0051607
    label: defense response to virus
  supported_by:
  - reference_id: PMID:37460672
    supporting_text: >-
      The highly diverse antiphage defence systems of bacteria
suggested_questions:
- question: >-
    Is GO:0004520 (DNA endonuclease activity) the correct MF term for SNIPE, or
    should
    a more specific child term (e.g. reflecting GIY-YIG family membership or the
    membrane-localized context) be used?
  experts: []
- question: >-
    Should the ManYZ pre-association be annotated as a separate protein complex,
    or is it
    better modelled as a GO-CAM causal association (SNIPE located_in plasma membrane,
    colocalizes_with ManYZ complex)?
  experts: []
- question: >-
    Does the tape measure protein (TMP) binding by DUF4041 warrant a specific MF
    annotation
    (e.g. viral protein binding) or is this better captured only in the GO-CAM model?
  experts: []
suggested_experiments:
- hypothesis: >-
    SNIPE cleaves phage DNA endonucleolytically (producing internal cuts) rather
    than
    exonucleolytically
  description: >-
    The 32P cleavage assay (Fig 2d) shows a smear of fragments consistent with
    endonucleolytic cleavage, but the exact cleavage mechanism and products have
    not been
    biochemically characterized with purified SNIPE. In vitro reconstitution of
    SNIPE
    nuclease activity with defined DNA substrates would confirm endonuclease vs
    exonuclease
    activity, determine sequence specificity (if any), and characterize cleavage
    products.
  experiment_type: Biochemical assay
- hypothesis: >-
    SNIPE homologues with non-TM N-terminal regions (DivIVA, T3SS, PH domain) use
    analogous mechanisms but target different phage entry pathways
  description: >-
    Test representative SNIPE homologues lacking TM domains for phage defence in
    their
    native hosts or heterologous expression. Determine whether these homologues
    also
    pre-associate with inner membrane proteins at genome injection sites, and whether
    their N-terminal domains dictate phage specificity.
  experiment_type: Genetics/Functional assay