Bacteriophage Virion Release and Host Cell Lysis Systems

A reusable module capturing the four principal bacteriophage progeny release architectures across bacterial hosts, structured as a variant set for host-envelope-aware pathway satisfiability and abduction: (1) the canonical three-step dsDNA phage lysis system for Gram-negative diderm hosts (holin / pinholin inner membrane pore formation, endolysin peptidoglycan degradation, and two-component Rz/Rz1 or unimolecular o-spanin outer membrane disruption), modulated in Tevenvirinae by antiholin-mediated lysis inhibition (LIN); (2) the two-step holin + endolysin system sufficient for Gram-positive monoderm hosts lacking an outer membrane (with an optional mycolate esterase LysB step in mycobacteriophages); (3) single-gene lysis (SGL) systems of small ssDNA and ssRNA phages that inhibit host peptidoglycan biosynthesis enzymes (such as MraY or MurA) or destabilize the cell envelope via an amrazin membrane protein; and (4) non-lytic chronic filamentous phage extrusion through a trans-envelope pIV/pI/pXI assembly complex.

MODULE:phage_virion_release_and_lysisCOMPLETECONCRETEBiological Processmodules/phage_virion_release_and_lysis.yaml
viral release from host cellGO:0019076 viral release from host cell by cytolysisGO:0044659
PMID:17900620
Rz/Rz1 lysis gene equivalents in phages of Gram-negative hosts.
In phages of Gram-negative hosts, the periplasm-spanning Rz-Rz1 two-component spanin complex (or a unimolecular u-spanin) connects the inner and outer membranes and is required for outer membrane disruption and host lysis in the presence of divalent cations.
Defects in Rz or Rz1 block lysis only in the presence of high concentrations of divalent cations.
PMID:22389108
Protein determinants of phage T4 lysis inhibition.
In phage T4, the T holin is regulated by the periplasmic RI antiholin to establish lysis inhibition in response to superinfection.
Genetic studies have established that lysis inhibition in bacteriophage T4 infections occurs when the RI antiholin inhibits the lethal hole-forming function of the T holin.
PMID:34456892
The Phage T4 Antiholin RI Has a Cleavable Signal Peptide, Not a SAR Domain.
Phage T4 RI functions as a secreted periplasmic antiholin that binds the periplasmic domain of the T holin to delay lysis triggering.
While regulation by the cytoplasmic RIII plays a minor role, the periplasmic antiholin RI binds tightly to the holin T and is believed to directly sense periplasmic phage DNA from superinfections as a trigger for the inhibition of lysis.
PMID:1201752
Studies on the specificity of action of bacteriophage T4 lysozyme.
Bacteriophage T4 endolysin (gpE) is a muramidase with lysozyme activity that cleaves host cell wall peptidoglycan during progeny release.
Analysis of the enzymatic degradation products shows that T4 acts as an endo-acetylmuramidase capable of cleaving glycosidic bonds only at muramic acid residues that are substituted with peptide side-chains.
PMID:4582731
Bacteriophage T7 lysozyme is an N-acetylmuramyl-L-alanine amidase.
Bacteriophage T7 gp3.5 endolysin cleaves the amide bond between N-acetylmuramic acid and L-alanine in host peptidoglycan.
file:projects/PHAGES.md
Bacteriophage Genome & Module Curation Plan
Defines the four mutually exclusive phage progeny release variants and documents the missing spanin and single-gene lysis ontology terms.
Four distinct routes—canonical 3-step `holin + endolysin + spanin` (λ, T7, T4), 2-step `holin + endolysin` without spanin (Gram-positive phages like φ29, SPO1; or mycolate-cleaving `Lysin A + Lysin B` in Mycobacteriophage L5), `single-gene lysis (Sgl)` inhibiting peptidoglycan biosynthesis (`GO:0039640` in φX174 `E` and Qβ `A2`, or membrane-lesion `L` in MS2), and non-lytic `chronic filamentous extrusion` (`GO:0099045` in M13).

Curated for the Bacteriophage Genome & Module Curation project. Because GO currently lacks dedicated molecular function terms for holin activity, endolysin catalytic grouping, spanin outer-membrane fusion activity, and amrazin-type single-gene lysis proteins, participants are anchored to the most specific available GO molecular functions (`GO:0140911` pore-forming activity for holins, `GO:0003796` lysozyme activity for endolysins, `GO:0140678` molecular function inhibitor activity for antiholins, and `GO:0004857` enzyme inhibitor activity for peptidoglycan-synthesis-inhibiting SGL proteins, while `function` is omitted on spanin, amrazin MS2 L, and filamentous extrusion annotons where GO lacks a dedicated molecular function term) paired with specific biological process terms (`GO:0044660`, `GO:0044659`, `GO:0039640`, `GO:0039639`, `GO:0099045`).

11Nodes
6Parts
1Variant Sets
4Variants
9Annotons
2Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

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

Leaf nodes lacking representative members

2 leaf node(s) with no concrete protein grounding:

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Function consistency and core coverage

0 gene-function check(s) reflected in core functions · 0 conflict(s) · 0 evidence or coverage gap(s) (6 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
holin_activity ANY_WITH_FUNCTION
Gene 		pore-forming activity
GO:0140911 		Participant Unchecked
No direct UniProt participant to compare. Abstract selectors and complex-wide activities cannot be inferred from donor or subunit gene reviews.
endolysin_muramidase_or_amidase ANY_WITH_FUNCTION
Gene 		lysozyme activity
GO:0003796 		Participant Unchecked
No direct UniProt participant to compare. Abstract selectors and complex-wide activities cannot be inferred from donor or subunit gene reviews.
antiholin_lysis_inhibition ANY_PARTICIPANT
Gene 		molecular function inhibitor activity
GO:0140678 		Participant Unchecked
No direct UniProt participant to compare. Abstract selectors and complex-wide activities cannot be inferred from donor or subunit gene reviews.
monoderm_holin_activity ANY_WITH_FUNCTION
Gene 		pore-forming activity
GO:0140911 		Participant Unchecked
No direct UniProt participant to compare. Abstract selectors and complex-wide activities cannot be inferred from donor or subunit gene reviews.
monoderm_endolysin_activity ANY_WITH_FUNCTION
Gene 		lysozyme activity
GO:0003796 		Participant Unchecked
No direct UniProt participant to compare. Abstract selectors and complex-wide activities cannot be inferred from donor or subunit gene reviews.
sgl_peptidoglycan_inhibitor ANY_WITH_FUNCTION
Gene 		enzyme inhibitor activity
GO:0004857 		Participant Unchecked
No direct UniProt participant to compare. Abstract selectors and complex-wide activities cannot be inferred from donor or subunit gene reviews.

Gene-review completeness (7/7 grounded genes reviewed)

7 complete review(s) · 3 with deep research · 0 missing review · 4 reviewed but lacking deep research

Gene Review Complete Deep research
E P00720 ✓ ✓ ✓
E P03639 ✓ ✓ ✗
IV P03665 ✓ ✓ ✗
L P03609 ✓ ✓ ✗
rI P13304 ✓ ✓ ✓
Rz P00726 ✓ ✓ ✗
t P06808 ✓ ✓ ✓

Details

Context
VirusesNCBITaxon:10239 BacteriaNCBITaxon:2
Bacteriophage Virion Release and Host Cell LysisBiological Processphage_virion_release_and_lysis
viral release from host cellGO:0019076 viral release from host cell by cytolysisGO:0044659
Context
VirusesNCBITaxon:10239 BacteriaNCBITaxon:2
Variant set: Bacteriophage virion release strategy by host envelope architecture and viral genome class (Exactly One)

Bacteriophages employ one of four release strategies depending on whether they are tailed dsDNA phages infecting diderm vs. monoderm hosts, small ssDNA/ssRNA phages encoding single-gene lysis proteins, or filamentous phages exiting by chronic non-lytic extrusion.

Gram-negative diderm three-step lysis (holin + endolysin + spanin)Biological Processdiderm_three_step_lysis

Sequential disruption of the inner membrane by a holin or pinholin (modulated in some phages by an antiholin), degradation of the periplasmic peptidoglycan meshwork by an endolysin, and disruption of the outer membrane by a two-component Rz/Rz1 i-spanin/o-spanin complex or unimolecular o-spanin.

Connections

positively regulatesRO:0002213
Holin pore formation releases canonical endolysin into the periplasm or depolarizes the inner membrane to release tethered SAR-endolysins.
positively regulatesRO:0002213
Removal of the cross-linked peptidoglycan meshwork liberates periplasm-spanning spanin complexes to oligomerize and disrupt the outer membrane.
Part 1: inner membrane holin pore formation
Holin inner membrane pore formationBiological Processholin_pore_formation

Annotons

Holin inner membrane pore-forming activity
holin_activity
Participant: Any With Function: t (Bacteriophage T4)
Gene Product:
t (Bacteriophage T4)UniProtKB:P06808
Required Function:
pore-forming activityGO:0140911
Phage holins and pinholins (such as T4 gpT, lambda S105, and T7 gp17.5) accumulate in the host inner membrane and trigger at an allele-specific time to collapse membrane potential and allow endolysin access or activation.

Function

pore-forming activityGO:0140911

Processes

viral release via pore formation in host cell membraneGO:0044660 viral release from host cell by cytolysisGO:0044659

Locations

host cell plasma membraneGO:0020002

Permeabilizes the host cytoplasmic membrane to release cytoplasmic endolysin into the periplasm or depolarize the membrane to activate SAR-endolysins.

PMID:22389108
Phage T4 holin T forms lesions in the host inner membrane at the time of lysis.
Genetic studies have established that lysis inhibition in bacteriophage T4 infections occurs when the RI antiholin inhibits the lethal hole-forming function of the T holin.
Part 2: periplasmic peptidoglycan degradation
Endolysin peptidoglycan degradationBiological Processendolysin_peptidoglycan_hydrolysis

Annotons

Endolysin peptidoglycan hydrolase activity
endolysin_muramidase_or_amidase
Participant: Any With Function: e (Bacteriophage T4)
Gene Product:
e (Bacteriophage T4)UniProtKB:P00720
Required Function:
lysozyme activityGO:0003796
Phage endolysins degrade the host peptidoglycan sacculus via muramidase/lysozyme activity (GO:0003796, e.g., T4 gpE), transglycosylase activity (lambda R), N-acetylmuramoyl-L-alanine amidase activity (GO:0008745, e.g., T7 gp3.5), or endopeptidase activity.

Function

lysozyme activityGO:0003796

Processes

viral release from host cell by cytolysisGO:0044659 peptidoglycan catabolic processGO:0009253

Locations

host cell periplasmic spaceGO:0044229

Cleaves the load-bearing peptidoglycan meshwork once holin pore formation grants access or triggers SAR release.

PMID:1201752
T4 endolysin hydrolyzes host cell wall peptidoglycan during phage lysis.
Analysis of the enzymatic degradation products shows that T4 acts as an endo-acetylmuramidase capable of cleaving glycosidic bonds only at muramic acid residues that are substituted with peptide side-chains.
Part 3: outer membrane disruption by spanin (optional)
Spanin-mediated outer membrane disruptionBiological Processspanin_outer_membrane_disruption

Annotons

Spanin trans-periplasmic outer membrane disruption
spanin_activity
Participant: Any Participant: Rz (Escherichia phage lambda)
Gene Product:
Rz (Escherichia phage lambda)UniProtKB:P00726
Two-component spanin complexes (inner membrane i-spanin Rz/pseT.3 paired with outer membrane lipoprotein o-spanin Rz1/pseT.2, or T7 gp18.5/gp18.7) or unimolecular o-spanins (T1 gp11) span the periplasm and undergo conformational collapse after peptidoglycan removal to fuse or disrupt the outer membrane.

Processes

viral release from host cell by cytolysisGO:0044659

Locations

host cell periplasmic spaceGO:0044229 host cell outer membraneGO:0039662

Completes lysis of diderm Gram-negative bacteria by disrupting the outer membrane once the peptidoglycan barrier is degraded.

PMID:17900620
In phages of Gram-negative hosts, the periplasm-spanning Rz-Rz1 two-component spanin complex (or a unimolecular u-spanin) connects the inner and outer membranes and is required for outer membrane disruption and host lysis in the presence of divalent cations.
Defects in Rz or Rz1 block lysis only in the presence of high concentrations of divalent cations.
Part 4: optional antiholin-mediated lysis inhibition (LIN) (optional)
Antiholin-mediated lysis inhibition (LIN)Biological Processantiholin_lysis_inhibition_regulation

Optional regulation of lysis timing (lysis inhibition, LIN) by periplasmic or cytoplasmic antiholins (such as T4 RI/RIII or lambda S107) that inhibit holin pore formation.

Annotons

Antiholin-mediated lysis inhibition (optional modulator)
antiholin_lysis_inhibition
Participant: Any Participant: rI (Bacteriophage T4)
Gene Product:
rI (Bacteriophage T4)UniProtKB:P13304
Periplasmic or membrane-associated antiholins (such as T4 RI, T4 RIII, and lambda S107) inhibit holin oligomerization in response to superinfection or before the scheduled lysis time.

Function

molecular function inhibitor activityGO:0140678

Processes

suppression by virus of host cell lysis in response to superinfectionGO:0039639

Locations

host cell periplasmic spaceGO:0044229

Inhibits holin triggering in response to secondary phage adsorption (lysis inhibition).

PMID:34456892
Phage T4 RI antiholin is secreted into the periplasm where it binds the T holin to delay lysis.
While regulation by the cytoplasmic RIII plays a minor role, the periplasmic antiholin RI binds tightly to the holin T and is believed to directly sense periplasmic phage DNA from superinfections as a trigger for the inhibition of lysis.
Gram-positive monoderm two-step lysis (holin + endolysin)Biological Processmonoderm_two_step_lysis

Phages infecting Gram-positive monoderm bacteria lack a spanin step because the host has no outer membrane; holin pore formation and endolysin peptidoglycan degradation suffice for cytolysis (augmented in mycobacteriophages by a LysB mycolylarabinogalactan esterase).

Part 1: monoderm holin pore formation
Monoderm phage holin pore formationBiological Processmonoderm_holin_step

Annotons

Holin pore-forming activity in monoderm host
monoderm_holin_activity
Participant: Any With Function: pore-forming activity
Required Function:
pore-forming activityGO:0140911
Holin of a Gram-positive phage (such as Bacillus phage phi29 gp14) that permeabilizes the cytoplasmic membrane.

Function

pore-forming activityGO:0140911

Processes

viral release via pore formation in host cell membraneGO:0044660

Locations

host cell plasma membraneGO:0020002

Permeabilizes the monoderm cytoplasmic membrane.

Part 2: monoderm endolysin cell wall cleavage
Monoderm phage endolysin cell wall hydrolysisBiological Processmonoderm_endolysin_step

Annotons

Endolysin peptidoglycan hydrolase activity in monoderm host
monoderm_endolysin_activity
Participant: Any With Function: lysozyme activity
Required Function:
lysozyme activityGO:0003796
Modular endolysin of a Gram-positive phage (such as phi29 gp15) combining a catalytic domain with cell-wall binding domains.

Function

lysozyme activityGO:0003796

Processes

viral release from host cell by cytolysisGO:0044659

Cleaves the thick Gram-positive peptidoglycan wall.

Single-gene lysis (SGL) in small ssDNA and ssRNA phagesBiological Processsingle_gene_lysis

Small single-stranded DNA (Microviridae) and RNA (Fiersviridae) phages encode a single lysis protein that either inhibits a specific host peptidoglycan biosynthesis enzyme ("protein antibiotics" such as phiX174 E inhibiting MraY or Qbeta A2 inhibiting MurA, annotated to GO:0039640) or disrupts envelope integrity without inhibiting murein synthesis (amrazins such as MS2 L, annotated to GO:0044659).

Annotons

Single-gene lysis by inhibition of host peptidoglycan biosynthesis
sgl_peptidoglycan_inhibitor
Participant: Any With Function: E (Escherichia phage phiX174)
Gene Product:
E (Escherichia phage phiX174)UniProtKB:P03639
Required Function:
enzyme inhibitor activityGO:0004857
Single-gene lysis proteins that inhibit host murein biosynthesis enzymes, including phiX174 gpE (inhibits MraY phospho-N-acetylmuramoyl-pentapeptide-transferase) and Qbeta A2 (maturation/coat-readthrough protein that inhibits MurA UDP-N-acetylglucosamine 1-carboxyvinyltransferase).

Function

enzyme inhibitor activityGO:0004857

Processes

viral release via suppression of host peptidoglycan biosynthetic processGO:0039640 viral release from host cell by cytolysisGO:0044659

Locations

host cell plasma membraneGO:0020002

Blocks host peptidoglycan precursor synthesis during cell division, causing septal lesions and osmotic cytolysis.

Single-gene lysis by amrazin envelope destabilization (MS2 L-type)
sgl_amrazin_envelope_disruption
Participant: Any Participant: L (Emesvirus zinderi)
Gene Product:
L (Emesvirus zinderi)UniProtKB:P03609
Amrazin-class single-gene lysis proteins (such as MS2 L) that trigger host cell cytolysis via DnaJ-chaperone-dependent envelope destabilization rather than inhibiting peptidoglycan biosynthesis.

Processes

viral release from host cell by cytolysisGO:0044659

Locations

host cell plasma membraneGO:0020002

Induces host cell cytolysis without inhibiting murein biosynthetic enzymes.

Non-lytic chronic filamentous extrusion (Inoviridae)Biological Processfilamentous_chronic_extrusion

Filamentous ssDNA phages (such as M13, fd, and f1) assemble and extrude progeny virions continuously across the host cell envelope via a trans-envelope secretin/ATPase assembly complex (pI/pXI inner membrane motor and pIV outer membrane secretin channel) without lysing the host cell.

Annotons

Filamentous phage trans-envelope extrusion machinery
filamentous_extrusion_machinery
Participant: Any Participant: IV (Enterobacteria phage M13)
Gene Product:
IV (Enterobacteria phage M13)UniProtKB:P03665
Trans-envelope filamentous phage assembly and export proteins (pI, pXI, and outer membrane secretin pIV) that extrude progeny virions while maintaining host membrane integrity.

Processes

viral extrusionGO:0099045

Locations

host cell outer membraneGO:0039662 host cell plasma membraneGO:0020002

Mediates non-lytic extrusion of filamentous phage particles across the bacterial cell envelope.