identifier: traitmech:000233 label: Septu system definition: A phage defense system in which an organism possesses a Septu locus encoding PtuA and the HNH endonuclease PtuB, whose PtuAB oligomer confers antiphage immunity through nuclease-mediated phage genome cleavage in standalone systems and can be regulated by retron RT-msDNA complexes in Retron-Septu loci. definition_source: DOI:10.1038/s41594-023-01172-8 trait_category: GENOMICS term_kind: CLASS mapping_status: PROPOSED parent_traits: - traitmech:000209 synonyms: - synonym_text: Septu synonym_type: EXACT_SYNONYM source: DOI:10.1126/science.aar4120 evidence: - reference: DOI:10.1126/science.aar4120 snippet: Septu PtuAB pfam13304, COG3950, pfam13395, pfam01844 ATPase, HNH nuclease 2,506 2,117 (4.1%) notes: Doron et al. reported Septu/PtuAB as an ATPase- and HNH-nuclease-linked system in their pangenome-scale antiphage-system discovery screen. - reference: DOI:10.1038/s41594-023-01172-8 snippet: 'E. coli Septu system, an anti-phage defense system, comprises two components: PtuA and PtuB' notes: Yang et al. support defining Septu as a two-component PtuA/PtuB antiphage system. - reference: DOI:10.1038/s41594-023-01172-8 snippet: PtuA contains an ATPase domain while PtuB is a nuclease that belongs to the His-Asn-His (HNH) family notes: Yang et al. support the ATPase and HNH endonuclease component classes that distinguish the PtuAB system. - reference: DOI:10.1038/s41594-023-01172-8 snippet: PtuAB restricts phage growth by cleaving phage genomic DNA notes: Yang et al. connect the PtuAB complex to nuclease-mediated restriction of phage growth in cells. - reference: DOI:10.1126/science.adv3344 snippet: The Retron-Septu system uniquely integrates retron and Septu antiphage defenses notes: Wang et al. support recognizing Retron-Septu as a Septu architecture with coupled retron regulation, not as a separate exact replacement for the broader Septu class. - reference: DOI:10.1126/science.adv3344 snippet: Activation occurs upon disassembly, releasing PtuAB, which degrades single-stranded DNA to restrict phage replication notes: Wang et al. connect Retron-Septu activation to release of PtuAB and DNA degradation that restricts phage replication. canonical_examples: - taxon_id: NCBITaxon:562 taxon_label: Escherichia coli note: Yang et al. structurally and functionally characterized an Escherichia coli Septu system in which PtuA and PtuB assemble into a 6:2 oligomer that restricts phage growth by cleaving phage genomic DNA. reference: DOI:10.1038/s41594-023-01172-8 causal_graphs: - graph_id: septu_ptuab_oligomer_nuclease_defense title: Septu PtuAB oligomers cleave phage genomic DNA description: Evidence-backed process sketch linking a Septu locus to PtuAB oligomer assembly, PtuB-dependent nuclease activity, cleavage of phage genomic DNA, and inhibition of phage replication. scope_status: NONMECHANISTIC scope_notes: The graph captures the shared PtuA/PtuB nuclease logic without asserting one exact activation trigger, ATP regulatory state, phage cue, target DNA modification, standalone-versus-retron architecture, or ssDNA-versus-genomic-DNA substrate across all Septu and Retron-Septu loci. nodes: - node_id: septu_locus label: Septu locus node_type: GENETIC_ELEMENT description: A Septu antiphage locus encoding a PtuA ATPase and cognate PtuB HNH nuclease. - node_id: ptuab_oligomer_assembly label: PtuAB oligomer assembly node_type: BIOLOGICAL_PROCESS description: Assembly of PtuA and PtuB into a higher-order antiphage complex. - node_id: ptuab_antiphage_activity label: PtuAB antiphage activity node_type: BIOLOGICAL_PROCESS description: PtuAB complex activity, dependent on PtuB nuclease activity, that restricts phage growth. - node_id: phage_genomic_dna_cleavage label: phage genomic DNA cleavage node_type: BIOLOGICAL_PROCESS description: Cleavage or degradation of phage genomic DNA by an activated PtuAB complex. - node_id: phage_growth label: phage growth node_type: BIOLOGICAL_PROCESS description: Bacteriophage growth and amplification inside a bacterial host population. - node_id: septu_system_trait label: Septu system node_type: TRAIT grounding: traitmech:000233 description: Possession of a genome-encoded Septu phage-defense system. - node_id: phage_defense_system label: phage defense system node_type: TRAIT grounding: traitmech:000209 description: Possession of one or more genome-encoded immune systems that inhibit bacteriophage infection. edges: - subject: septu_locus predicate: contributes to predicate_id: RO:0002326 object: ptuab_oligomer_assembly description: The Septu locus encodes PtuA and PtuB components that assemble into a higher-order PtuAB complex. evidence: - reference: DOI:10.1038/s41594-023-01172-8 snippet: PtuA and PtuB form a stable complex with a 6:2 stoichiometry notes: Yang et al. support assembly of the PtuA and PtuB Septu components. - subject: ptuab_oligomer_assembly predicate: enables predicate_id: RO:0002327 object: ptuab_antiphage_activity description: PtuAB assembly is critical for antiphage activity. evidence: - reference: DOI:10.1038/s41594-023-01172-8 snippet: the assembly of PtuAB is critical for its anti-phage activity notes: Yang et al. support a functional connection between PtuAB assembly and antiphage activity. - subject: ptuab_antiphage_activity predicate: enables predicate_id: RO:0002327 object: phage_genomic_dna_cleavage description: The PtuAB complex restricts phage growth by cleaving phage genomic DNA. evidence: - reference: DOI:10.1038/s41594-023-01172-8 snippet: E. coli anti-phage defense mediated by PtuAB via degrading the phage genomic DNA notes: Yang et al. connect PtuAB activity to cleavage of phage genomic DNA. - subject: phage_genomic_dna_cleavage predicate: mitigates predicate_id: METPO:2007407 object: phage_growth description: PtuAB-mediated cleavage of phage genomic DNA restricts phage growth. evidence: - reference: DOI:10.1038/s41594-023-01172-8 snippet: PtuAB restricts phage growth by cleaving phage genomic DNA notes: Yang et al. connect PtuAB nuclease activity to reduced phage growth. - subject: phage_genomic_dna_cleavage predicate: confers predicate_id: METPO:2007700 object: septu_system_trait description: PtuAB-mediated phage genomic DNA cleavage realizes the Septu system trait. evidence: - reference: DOI:10.1038/s41594-023-01172-8 snippet: PtuAB can confer bacteria immune defense against phage infection by digesting phage genomic DNA in a species-dependent way notes: Yang et al. support the DNA-digestion logic of PtuAB antiphage defense. - subject: septu_system_trait predicate: is a predicate_id: rdfs:subClassOf object: phage_defense_system description: Septu system possession is a phage-defense-system trait. evidence: - reference: DOI:10.1126/science.aar4120 snippet: Septu PtuAB pfam13304, COG3950, pfam13395, pfam01844 ATPase, HNH nuclease 2,506 2,117 (4.1%) notes: Doron et al. reported Septu in a table of candidate antiphage defense systems. discussions: - discussion_id: septu-standalone-retron-regulation-gap prompt: Resolve standalone Septu activation, Retron-Septu release, and DNA-substrate specificity before minting narrower Septu mechanism children. kind: KNOWLEDGE_GAP status: OPEN rationale: Yang et al. support a standalone Escherichia coli PtuAB system in which ATP modulates PtuA/PtuB nuclease activity through an incompletely resolved phage trigger, and Wang et al. support Retron-Septu Ec83/Ec78 complexes in which retron RT-msDNA association keeps PtuAB inactive until disassembly. The first TraitRecord therefore stays at the PtuA/PtuB system level until separate review resolves standalone activation, retron-dependent release, target DNA classes, and phage-specific activity across Septu loci. posed_by: codex posed_date: '2026-09-15' curation_history: - timestamp: '2026-09-15T23:58:00Z' curator: codex action: MINTED_TRAITMECH_ID changes: Minted Septu system as a DOI-backed GENOMICS TraitRecord under the phage defense system parent after an ignored-and-hidden duplicate review found no exact live TraitMech, METPO, or prior proposal record; the replacement placeholder is reserved in proposals/metpo_traitmech_v110. llm_assisted: true