Anti-CRISPR suppression of host CRISPR-Cas immunity

Proteins encoded by bacteriophages, archaeal viruses, prophages and other mobile genetic elements suppress host CRISPR-Cas immunity through alternative mechanisms. These include blocking effector assembly or target recognition, sequestering an effector subunit or disabling its nuclease, modifying Cas proteins, cleaving guide RNA, and degrading an immune second messenger. A mobile element may combine several inhibitors, but these are not compulsory sequential steps. Optional anti-CRISPR-associated regulators control inhibitor expression. The examples span bacterial and archaeal hosts; plasmid and conjugative-element inhibitors need not have a viral origin.

MODULE:anti_crispr_suppressionDRAFTCONCRETEBiological Processmodules/anti_crispr_suppression.yaml
symbiont-mediated suppression of host CRISPR-cas systemGO:0098672
PMID:23242138
Phage genes can inhibit bacterial CRISPR-Cas immunity.
PMID:26416740
Different anti-CRISPR proteins independently inhibit target-DNA binding or downstream nuclease recruitment.
PMID:32503371
Review distinguishes stoichiometric inhibitors from enzymatic modifications and signal degradation; the families have diverse structures and mechanisms.
PMID:32186918
Review surveys anti-CRISPR proteins produced by viruses and other mobile elements.
PMID:32218510
AcrIIA16–19 occur in plasmids, conjugative elements, prophages and other contexts; defined inhibitors protect targeted plasmids during Enterococcus faecalis conjugation. Mobile-element origin is not synonymous with viral origin.
PMID:38987591
Aca2 represses transcription by binding DNA and represses translation by binding RNA stem-loops that limit ribosome access.
PMID:40240860
The Comment tested native SIRV2 gp37 and SIRV1 gp29 transplanted into SIRV2, with early-expression rescue. It did not test native SIRV1 infection. Physiological generalization remains disputed.
PMID:40240850
The Reply disputes physiological generalization of the infection experiments and raises possible experimental confounders; these remain objections attributed to its authors.

The participant taxon envelope includes viral proteins and proteins deposited under bacterial genomes, including prophages and nonviral mobile elements. Hosts are bacteria or archaea as specified for each experimental system; heterologous human-cell editing assays do not extend the native host range. Inhibitory occupancy depends on affinity, concentration, binding stoichiometry and timing: a stoichiometric blocker does not universally require molar excess. Catalytic turnover can permit substoichiometric inhibition in vitro without establishing effective native expression. Families are sampled by tested members; conserved membership alone does not establish all targets or native counterdefense. Host CRISPR functions are described separately in MODULE:crispr_cas_adaptive_immunity. Host self-regulatory ring nucleases and unrelated anti-defense mechanisms remain outside the functional boundary.

15Nodes
2Parts
1Variant Sets
12Variants
14Annotons
0Connections

Derived QC

Recommended-field compliance

76.9% recommended fields populated
  • knowledge_gaps[0] · provenance (0/1)
  • knowledge_gaps[1] · provenance (0/1)
  • knowledge_gaps[2] · provenance (0/1)

Module deep research

✗ none found

No MODULE:anti_crispr_suppression deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Function consistency and core coverage

10 gene-function check(s) reflected in core functions · 0 conflict(s) · 13 evidence or coverage gap(s) (23 comparison(s))

Retained noncore functions are reported separately; they do not require promotion to core functions. Support from representative genes does not establish conservation across the whole family. Missing reviews or identifiers leave a claim unverified.

AnnotonParticipantFunctionAssessment
acrif8_csy_blocker ZF40_0031 / acrIF8 (Pectobacterium phage ZF40)
UniProtKB:H9C181
Family Representative 		ribonucleoprotein complex binding
GO:0043021 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
acrif2_csy_blocker orf30 / gp30 (Pseudomonas phage D3112)
UniProtKB:Q6TM72
Family Representative 		nucleic acid mimicry-based competitive inhibitor activity
No function ID 		No Function Id
A gene review exists, but this function lacks a GO identifier. Free-text chemistry is not automatically compared.
acriia4_dna_mimic acrIIA4 (Listeria monocytogenes prophage)
UniProtKB:A0A247D711
Family Representative 		DNA mimicry-based competitive occlusion of the Cas9 PAM-recognition site
No function ID 		No Function Id
A gene review exists, but this function lacks a GO identifier. Free-text chemistry is not automatically compared.
acriic2_assembly_inhibitor acrIIC2 (Neisseria meningitidis)
UniProtKB:A0A425B3G2
Gene 		Cas9 ribonucleoprotein assembly inhibitor activity
GO:0140721 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
acrif3_cas3_sequestration JBD5_035 / acrIF3 (Pseudomonas phage JBD5)
UniProtKB:L7P7R7
Family Representative 		protein sequestering activity
GO:0140311 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
acriic1_hnh_blocker acrIIC1 (Neisseria meningitidis prophage)
UniProtKB:A0A2D0TCG3
Family Representative 		nuclease inhibitor activity
GO:0140721 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
acrid1_cas10d_sequesterer acrID1 / gp02 (Sulfolobus islandicus rod-shaped virus 3)
UniProtKB:A0A1B3SN05
Gene 		protein sequestering activity
GO:0140311 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
acrvia1_cas13a_blocker acrVIA1 (Listeria seeligeri phage phiLS46 gp2)
UniProtKB:A0A6P3CWF5
Gene 		Cas13a target-RNA recognition inhibitor activity
GO:0140721 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
acrva1_crrna_nuclease acrVA1 (Moraxella bovoculi)
UniProtKB:A0A5H1ZR47
Family Representative 		RNA endonuclease activity
GO:0004521 		Annotation Supported
A retained annotation or curated replacement supports this function, but core_functions does not yet reflect it.
acriii1_ring_nuclease orf114 / gp29 / AcrIII-1 (Sulfolobus islandicus rod-shaped virus 1)
UniProtKB:Q8QL27
Gene 		cyclic oligoadenylate ring nuclease activity
No function ID 		No Function Id
A gene review exists, but this function lacks a GO identifier. Free-text chemistry is not automatically compared.
acrva5_cas12a_acetyltransferase acrVA5 / AAX07_09540 (Moraxella bovoculi)
UniProtKB:A0A0U2B867
Gene 		Cas12a lysine acetyltransferase activity
GO:0061733 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
aca2_repressor ZF40_0030 / aca2 (Pectobacterium phage ZF40)
UniProtKB:H9C180
Family Representative 		DNA-binding transcription repressor activity
GO:0001217 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
aca2_translation_repressor ZF40_0030 / aca2 (Pectobacterium phage ZF40)
UniProtKB:H9C180
Family Representative 		RNA binding
GO:0003723 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
aca2_translation_repressor:required_function ZF40_0030 / aca2 (Pectobacterium phage ZF40)
UniProtKB:H9C180
Family Representative 		DNA-binding transcription repressor activity
GO:0001217 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
acrif8_csy_blocker AcrF8 (AcrIF8) anti-CRISPR family
InterPro:IPR057730
Family 		ribonucleoprotein complex binding
GO:0043021 		Family Review Missing
No supported structured family review is available for InterPro:IPR057730.
acrif2_csy_blocker AcrF2 anti-CRISPR family
InterPro:IPR057728
Family 		nucleic acid mimicry-based competitive inhibitor activity
No function ID 		No Function Id
The family function has no GO identifier for comparison; prose is not matched.
acriia4_dna_mimic AcrIIA4-like anti-CRISPR family
InterPro:IPR056215
Family 		DNA mimicry-based competitive occlusion of the Cas9 PAM-recognition site
No function ID 		No Function Id
The family function has no GO identifier for comparison; prose is not matched.
acrif3_cas3_sequestration AcrF3-like Cas3 inhibitor family
InterPro:IPR049085
Family 		protein sequestering activity
GO:0140311 		Family Review Missing
No supported structured family review is available for InterPro:IPR049085.
acriic1_hnh_blocker AcrIIC1 anti-CRISPR family
InterPro:IPR064626
Family 		nuclease inhibitor activity
GO:0140721 		Family Review Missing
No supported structured family review is available for InterPro:IPR064626.
acrva1_crrna_nuclease AcrVA1-like anti-CRISPR family
InterPro:IPR064663
Family 		RNA endonuclease activity
GO:0004521 		Family Review Missing
No supported structured family review is available for InterPro:IPR064663.
aca2_repressor Aca2/YdiL-like anti-CRISPR-associated repressor family
InterPro:IPR015060
Family 		DNA-binding transcription repressor activity
GO:0001217 		Family Review Missing
No supported structured family review is available for InterPro:IPR015060.
aca2_translation_repressor Aca2/YdiL-like anti-CRISPR-associated repressor family
InterPro:IPR015060
Family 		RNA binding
GO:0003723 		Family Review Missing
No supported structured family review is available for InterPro:IPR015060.
aca2_translation_repressor:required_function Aca2/YdiL-like anti-CRISPR-associated repressor family
InterPro:IPR015060
Family 		DNA-binding transcription repressor activity
GO:0001217 		Family Review Missing
No supported structured family review is available for InterPro:IPR015060.

Gene-review completeness (13/13 grounded genes reviewed)

11 complete review(s) · 2 with deep research · 0 missing review · 11 reviewed but lacking deep research

Gene Review Complete Deep research
114 Q8QL27 ✓ 3/4 ✗
aca2 H9C180 ✓ ✓ ✓
AcrF8 H9C181 ✓ ✓ ✓
acrID1 A0A1B3SN05 ✓ ✓ ✗
acrIF3 L7P7R7 ✓ ✓ ✗
acrIIA2 A0A059T5F6 ✓ ✓ ✗
acrIIA4 A0A247D711 ✓ ✓ ✗
acrIIC1 A0A2D0TCG3 ✓ ✓ ✗
acrIIC2 A0A425B3G2 ✓ ✓ ✗
acrVA1 A0A5H1ZR47 ✓ ✓ ✗
acrVA5 A0A0U2B867 ✓ 0/0 ✗
acrVIA1 A0A6P3CWF5 ✓ ✓ ✗
orf30 Q6TM72 ✓ ✓ ✗

Details

Context
VirusesNCBITaxon:10239 BacteriaNCBITaxon:2
host cell cytoplasmGO:0030430 cytoplasmGO:0005737
anti-CRISPR suppression of host CRISPR-Cas immunityBiological Processanti_crispr_suppression
symbiont-mediated suppression of host CRISPR-cas systemGO:0098672
Context
VirusesNCBITaxon:10239 BacteriaNCBITaxon:2
host cell cytoplasmGO:0030430 cytoplasmGO:0005737
Part: One or more alternative counterdefense mechanisms
alternative anti-CRISPR mechanismsBiological Processcounterdefense_routes
Variant set: independent inhibition mechanisms by effector target and inhibitory mechanism (One Or More)

A realization uses a compatible inhibitor and susceptible host target. These variants are alternatives that may coexist, not an obligate series; the AcrIII-1 branch additionally requires a permissive expression context.

AcrIF8: Csy/crRNA blockadeBiological Processacrif8_recognition_blockade

AcrIF8 uses protein and guide-RNA contacts to inhibit the tested type I-F complex.

Annotons

AcrIF8 Csy complex and crRNA-contacting blocker
acrif8_csy_blocker
Participant: Family: AcrF8 (AcrIF8) anti-CRISPR family
Family:
AcrF8 (AcrIF8) anti-CRISPR familyInterPro:IPR057730 Official InterPro API verification places H9C181 in IPR057730 across residues 1–92; the family integrates Pfam PF25699. CDD cd22241 independently corroborates AcrIF8 identity. Raw responses and retrieval provenance are preserved in modules/anti_crispr_suppression-source-analysis/README.md.
Representative Members: ZF40_0031 / acrIF8 (Pectobacterium phage ZF40)UniProtKB:H9C181

Function

ribonucleoprotein complex bindingGO:0043021
Targets: host type I-F Csy surveillance complex (Cas7f backbone and crRNA)

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

Occupies the Csy ribonucleoprotein complex and prevents productive R-loop formation. Inhibitory occupancy is stoichiometric; no universal molar-excess threshold is asserted.

AcrIF2: DNA mimicry at CascadeBiological Processacrif2_recognition_blockade

DNA mimicry can inhibit distinct class 1 surveillance systems, with effector-specific susceptibility.

Annotons

AcrIF2-family Csy complex blocker
acrif2_csy_blocker
Participant: Family: AcrF2 anti-CRISPR family
Family:
AcrF2 anti-CRISPR familyInterPro:IPR057728
Representative Members: orf30 / gp30 (Pseudomonas phage D3112)UniProtKB:Q6TM72

Function

nucleic acid mimicry-based competitive inhibitor activity An acidic DNA-mimicking surface occupies the DNA-capture region of the surveillance complex.
Targets: host type I-F Cas8f/Cas7f DNA-capture pocket

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

Prevents target-DNA engagement by susceptible surveillance complexes; type I-F and selected type I-C activity are compatible with one inhibitor.

PMID:23242138
The D3112 inhibitor was identified in phage counterdefense.
PMID:36805026
AcrIF2 also inhibits the tested Desulfovibrio vulgaris type I-C system; activity against one subtype or ortholog does not imply universal susceptibility.
AcrIIA4: Cas9 PAM-site occlusionBiological Processacriia4_recognition_blockade

A DNA mimic blocks target recognition and access to a nuclease pocket in RNA-loaded SpyCas9.

Annotons

AcrIIA4 PAM-duplex mimic
acriia4_dna_mimic
Participant: Family: AcrIIA4-like anti-CRISPR family
Family:
AcrIIA4-like anti-CRISPR familyInterPro:IPR056215
Representative Members: acrIIA4 (Listeria monocytogenes prophage)UniProtKB:A0A247D711

Function

DNA mimicry-based competitive occlusion of the Cas9 PAM-recognition site An acidic surface mimics target DNA at sgRNA-loaded SpyCas9, occupying PAM-recognition and RuvC-access surfaces.
Targets: host Cas9 PAM-interacting domain host Cas9 RuvC non-target-strand cleavage pocket

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

Inhibits productive target binding by susceptible RNA-loaded Cas9; this is a time- and effector-dependent mechanism, not universal reversal of already bound Cas9.

AcrIIA2: convergent Cas9 DNA mimicryBiological Processacriia2_recognition_blockade

The LP-101 representative is an ortholog-based example of a separately characterized DNA-mimic family.

Annotons

AcrIIA2 DNA-mimicking Cas9 inhibitor
acriia2_dna_mimic
Participant: Gene Product: LP101_024 / acrIIA2 (Listeria phage LP-101)
Gene Product:
LP101_024 / acrIIA2 (Listeria phage LP-101)UniProtKB:A0A059T5F6 LP-101 AcrIIA2 ortholog. Existing notes identify nine residue differences from the directly assayed prophage protein; structural mechanism is ortholog-supported rather than an exact LP-101 construct assay.

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

A distinct AcrIIA2 family converges on Cas9 target-site occlusion. Sequence identity and target specificity must be checked for individual orthologs.

PMID:30606466
Characterized AcrIIA2 proteins inhibit Cas9 through DNA mimicry at the PAM-recognition surface; exact LP-101 construct identity is not asserted.
AcrIIC2: guide-loading blockadeBiological Processacriic2_assembly_blockade

Binding apo-Cas9 prevents effector ribonucleoprotein assembly, an alternative to attacking an assembled effector.

Annotons

AcrIIC2 Cas9 assembly inhibitor
acriic2_assembly_inhibitor
Participant: Gene Product: acrIIC2 (Neisseria meningitidis)
Gene Product:
acrIIC2 (Neisseria meningitidis)UniProtKB:A0A425B3G2

Function

Cas9 ribonucleoprotein assembly inhibitor activityGO:0140721
Targets: Nme1Cas9 bridge helix

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

Acts before a functional Cas9–guide complex forms; it need not first block target-DNA recognition.

AcrIF3: Cas2/3 sequestrationBiological Processacrif3_nuclease_sequestration

In the tested type I-F system a separate nuclease-helicase is sequestered. This does not describe all class 1 effector architectures.

Annotons

AcrF3 Cas3 sequestering inhibitor
acrif3_cas3_sequestration
Participant: Family: AcrF3-like Cas3 inhibitor family
Family:
AcrF3-like Cas3 inhibitor familyInterPro:IPR049085
Representative Members: JBD5_035 / acrIF3 (Pseudomonas phage JBD5)UniProtKB:L7P7R7
Required Function:
protein sequestering activityGO:0140311

Function

protein sequestering activityGO:0140311
Targets: host type I-F Cas3 helicase-nuclease

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

AcrIF3 binds the type I-F Cas2/3 nuclease-helicase and prevents productive recruitment to the target-bound Csy complex. DNA recognition can remain intact.

AcrIIC1: Cas9 HNH-domain inhibitionBiological Processacriic1_catalytic_blockade

A catalytic-domain inhibitor can preserve target occupancy while inhibiting cleavage.

Annotons

AcrIIC1 broad-spectrum Cas9 HNH inhibitor
acriic1_hnh_blocker
Participant: Family: AcrIIC1 anti-CRISPR family
Family:
AcrIIC1 anti-CRISPR familyInterPro:IPR064626
Representative Members: acrIIC1 (Neisseria meningitidis prophage)UniProtKB:A0A2D0TCG3

Function

nuclease inhibitor activityGO:0140721 Binding the conserved HNH domain inhibits nuclease function while permitting target-DNA association in the tested Cas9 systems.
Targets: host Cas9 HNH nuclease domain

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

Suppresses cleavage by susceptible Cas9 proteins; broad activity across tested orthologs is not universal inhibition of all Cas9 enzymes.

AcrID1: archaeal Cas10d sequestrationBiological Processacrid1_subunit_sequestration

A viral inhibitor disrupts subtype I-D effector assembly by trapping Cas10d in a nonfunctional oligomer.

Annotons

AcrID1 Cas10d sequestering inhibitor
acrid1_cas10d_sequesterer
Participant: Gene Product: acrID1 / gp02 (Sulfolobus islandicus rod-shaped virus 3)
Gene Product:
acrID1 / gp02 (Sulfolobus islandicus rod-shaped virus 3)UniProtKB:A0A1B3SN05

Function

protein sequestering activityGO:0140311
Targets: type I-D Cas10d large subunit

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

Sequesters a large subunit whose HD nuclease and polymerase-like architecture differ from the separate type I-F Cas2/3 recruitment target. The completed target-bound effector complex resists inhibition under the tested conditions.

AcrVIA1: RNA-target recognition and activation blockadeBiological Processacrvia1_rna_target_blockade

Type VI-A counterdefense inhibits an RNA-targeting immune effector rather than a DNA nuclease.

Annotons

AcrVIA1 Lse Cas13a blocker
acrvia1_cas13a_blocker
Participant: Gene Product: acrVIA1 (Listeria seeligeri phage phiLS46 gp2)
Gene Product:
acrVIA1 (Listeria seeligeri phage phiLS46 gp2)UniProtKB:A0A6P3CWF5 The 229-residue UniProt sequence maps directly to PDB 6VRB. The discovery paper describes native gp2 as 232 residues; that sequence-length discrepancy is retained as a construct/provenance limitation, not silently resolved.

Function

Cas13a target-RNA recognition inhibitor activityGO:0140721
Targets: guide-exposed face of Listeria seeligeri Cas13a

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

Prevents both target-RNA recognition and activation of collateral RNA cleavage in the susceptible Cas13a system. Native specificity and the phiLS46 sequence distinguish it from unrelated proteins sharing an AcrVIA name.

AcrVA1: Cas12a-dependent guide cleavageBiological Processacrva1_guide_cleavage

Guide cleavage and PAM-pocket interference inhibit susceptible Cas12a complexes through overlapping mechanisms.

Annotons

AcrVA1 crRNA-cleaving inhibitor of Cas12a
acrva1_crrna_nuclease
Participant: Family: AcrVA1-like anti-CRISPR family
Family:
AcrVA1-like anti-CRISPR familyInterPro:IPR064663
Representative Members: acrVA1 (Moraxella bovoculi)UniProtKB:A0A5H1ZR47

Function

RNA endonuclease activityGO:0004521 Cas12a-dependent guide cleavage is experimentally established. The original biochemical paper did not identify the catalytic component; later structural work assigns an RNase site to AcrVA1 helix alpha2. This is not autonomous cleavage of free guide RNA.
Substrates: Cas12a-bound crRNA guide
Products: Cas12a-bound 5-prime crRNA fragment and released targeting 3-prime fragment

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

Truncates the targeting region of Cas12a-bound crRNA and can act under substoichiometric assay conditions. The retained 5-prime fragment means the product is not simply apo-Cas12a; irreversibility in every assay context is not asserted.

AcrIII-1: cA4 destruction with disputed native deploymentBiological Processacriii1_signal_degradation

cA4 degradation can dampen the cA4-dependent accessory-defense branch of type III systems. It does not abolish every type III activity: direct RNA cleavage, Cas10 nuclease activity and other cyclic-oligonucleotide specificities are distinct.

Annotons

AcrIII-1 viral cyclic oligoadenylate ring nuclease
acriii1_ring_nuclease
Participant: Gene Product: orf114 / gp29 / AcrIII-1 (Sulfolobus islandicus rod-shaped virus 1)
Gene Product:
orf114 / gp29 / AcrIII-1 (Sulfolobus islandicus rod-shaped virus 1)UniProtKB:Q8QL27 Exact assayed protein established by RefSeq NP_666617 and PDB 6SCF/2X4I. DUF1874/STIV B116-like membership is not sufficient to classify every homolog as a native anti-CRISPR.

Function

cyclic oligoadenylate ring nuclease activity A homodimeric ring nuclease cleaves cA4 to linear diadenylate with a 2-prime,3-prime cyclic phosphate.
Substrates: cyclic tetra-adenylate (cA4)
Products: linear diadenylate with a 2-prime,3-prime cyclic phosphate (ApA>p)

Established cA4 chemistry provides a conditional suppression capability. Its contribution during native viral infection remains disputed, so no unconditional GO:0098672 process assertion is attached to this representative.

PMID:40240860
Native SIRV2 gp37 and SIRV1 gp29 transplanted into SIRV2 did not provide protection under the tested expression conditions; earlier expression rescued protection. Native SIRV1 infection was not directly tested.
PMID:40240850
The Reply challenges extrapolation to native physiology and identifies possible experimental confounders. The exchange does not negate the established cA4 cleavage.
AcrVA5: covalent Cas12a acetylationBiological Processacrva5_covalent_modification

Catalytic transfer of an acetyl group blocks target recognition without requiring permanent occupancy of the effector.

Annotons

AcrVA5 Cas12a acetyltransferase
acrva5_cas12a_acetyltransferase
Participant: Gene Product: acrVA5 / AAX07_09540 (Moraxella bovoculi)
Gene Product:
acrVA5 / AAX07_09540 (Moraxella bovoculi)UniProtKB:A0A0U2B867 Official UniSave version 17 of deleted UniProtKB A0A0U2B867; the 92-residue sequence matches PDB 6IUF apart from its N-terminal PLGS construct tag. Archived identity is preserved explicitly, not presented as a current UniProtKB record.

Function

Cas12a lysine acetyltransferase activityGO:0061733
Substrates: acetyl-CoA unmodified Cas12a lysine
Products: CoA N6-acetyllysine-containing Cas12a
Targets: PAM-recognition lysine of susceptible Cas12a

Processes

symbiont-mediated suppression of host CRISPR-cas systemGO:0098672

Covalently modifies a Cas protein instead of destroying it. Inhibition depends on the susceptible lysine and can be reversed enzymatically; GNAT-like fold membership does not establish anti-CRISPR function.

Part: Optional local control of inhibitor expression (optional)
Aca2 DNA/RNA autoregulationRegulatory Stepaca_autoregulation

The ZF40 acrIF8–aca2 locus couples inhibitor expression to a regulator that represses its own operon at transcriptional and translational levels. The loop regulates expression rather than sensing whether Cas inhibition has succeeded. Other loci may lack Aca2 or use distinct regulators.

Annotons

Aca2 anti-CRISPR-associated repressor
aca2_repressor
Participant: Family: Aca2/YdiL-like anti-CRISPR-associated repressor family
Family:
Aca2/YdiL-like anti-CRISPR-associated repressor familyInterPro:IPR015060 This selector refers to anti-CRISPR-associated repressors with a demonstrated regulated locus; Aca2/YdiL-like homology alone does not establish the target operon or every regulatory mode.
Representative Members: ZF40_0030 / aca2 (Pectobacterium phage ZF40)UniProtKB:H9C180
Required Function:
DNA-binding transcription repressor activityGO:0001217

Function

DNA-binding transcription repressor activityGO:0001217
Targets: shared aca2-acr promoter operator

Processes

negative regulation of DNA-templated transcriptionGO:0045892

Controls the abundance of the ZF40 AcrIF8 inhibitor through negative feedback on its shared operon. Aca2 is not itself a Cas inhibitor and need not sense successful immune suppression.

Aca2 RNA-dependent translational repression
aca2_translation_repressor
Participant: Family: Aca2/YdiL-like anti-CRISPR-associated repressor family
Family:
Aca2/YdiL-like anti-CRISPR-associated repressor familyInterPro:IPR015060 This selector refers to anti-CRISPR-associated repressors with a demonstrated regulated locus; Aca2/YdiL-like homology alone does not establish the target operon or every regulatory mode.
Representative Members: ZF40_0030 / aca2 (Pectobacterium phage ZF40)UniProtKB:H9C180
Required Function:
DNA-binding transcription repressor activityGO:0001217

Function

RNA bindingGO:0003723
Targets: conserved stem-loops in acrIF8–aca2 mRNA

Processes

negative regulation of translationGO:0017148

RNA recognition limits translation from the regulated transcript; this mode complements promoter repression in the characterized Aca2 system.