identifier: traitmech:000333 label: NixI system definition: A phage defense system in which an organism possesses a NixI-family phage-satellite locus represented by the DefenseFinder NixI__NixI profile and exemplified by a PLE-encoded nicking endonuclease that cleaves ICP1 bacteriophage DNA, inhibits ICP1 genome replication, and reduces progeny production in Vibrio cholerae. definition_source: DOI:10.1093/nar/gkac002 trait_category: GENOMICS term_kind: CLASS mapping_status: PROPOSED parent_traits: - traitmech:000209 synonyms: - synonym_text: NixI synonym_type: RELATED_SYNONYM source: https://raw.githubusercontent.com/mdmparis/defense-finder-models/afb0e5a8b466be53586b13266f5d38d98c3ac268/List_system_article.md evidence: - reference: DOI:10.1093/nar/gkac002 snippet: Here, we characterize a PLE-encoded nuclease, NixI, that blocks phage development likely by nicking ICP1’s genome as it transitions to RCR notes: LeGault et al. characterize NixI as a PLE-encoded nuclease that likely blocks ICP1 development by nicking the ICP1 genome as it transitions to rolling-circle replication. - reference: DOI:10.1093/nar/gkac002 snippet: Together, these data show that PLE encodes a nicking endonuclease, NixI, that is necessary for cleavage of ICP1’s genome in vivo and that shows in vitro specificity for sequences found in ICP1’s genome notes: LeGault et al. show that NixI is a PLE-encoded nicking endonuclease necessary for in vivo ICP1 cleavage and specific for ICP1-derived sequences in vitro. - reference: DOI:10.1093/nar/gkac002 snippet: NixI, however, is sufficient to limit ICP1 progeny production in a single round of infection notes: LeGault et al. support NixI as a PLE-encoded product sufficient to limit ICP1 progeny production in a single infection round. - reference: DOI:10.1093/nar/gkac002 snippet: Together, these data demonstrate that nixI is a potent inhibitor of ICP1 replication, resulting in decreased virion production. notes: LeGault et al. support NixI as a potent inhibitor of ICP1 genome replication, resulting in decreased virion production. - reference: DOI:10.1093/nar/gkac002 snippet: Phage parasites can be considered host defense systems, as the parasite inhibits production of its viral host, benefiting the bacterial population notes: LeGault et al. explicitly frame PLE-like phage parasites as host defense systems because they inhibit production of their viral hosts. - reference: https://raw.githubusercontent.com/mdmparis/defense-finder-models/afb0e5a8b466be53586b13266f5d38d98c3ac268/List_system_article.md snippet: NixI | 10\.1101/2021\.07\.12\.452122 | A phage parasite deploys a nicking nuclease effector to inhibit replication of its viral host notes: The DefenseFinder article registry maps the named NixI model namespace to the LeGault et al. PLE-encoded nicking-nuclease preprint, later published under DOI:10.1093/nar/gkac002. - reference: https://raw.githubusercontent.com/mdmparis/defense-finder-models/afb0e5a8b466be53586b13266f5d38d98c3ac268/DefenseFinder_rules.tsv snippet: "NixI\tNixI\t1\t1\tNixI__NixI\tNixI__Stix\t\t" notes: The DefenseFinder rules table models NixI with the NixI__NixI profile as its mandatory component and an optional NixI__Stix profile. - reference: https://raw.githubusercontent.com/mdmparis/defense-finder-models/afb0e5a8b466be53586b13266f5d38d98c3ac268/Liste_hmm_system.md snippet: '| NixI__NixI | NixI__NixI | NixI | Custom | 20 |' notes: The DefenseFinder HMM inventory records NixI__NixI under the NixI model namespace. canonical_examples: - taxon_id: NCBITaxon:666 taxon_label: Vibrio cholerae note: LeGault et al. used PLE-positive Vibrio cholerae to show that NixI-dependent cleavage sites appear in ICP1 during infection and that nixI inhibits ICP1 replication and progeny production. reference: DOI:10.1093/nar/gkac002 causal_graphs: - graph_id: nixi_locus_inhibits_icp1_replication title: NixI loci inhibit ICP1 replication description: Conservative system-level sketch linking a NixI-family phage-satellite locus to ICP1 genome cleavage, ICP1 replication inhibition, and the NixI system trait. scope_status: NONMECHANISTIC scope_notes: The graph captures NixI as a named DefenseFinder single-mandatory-profile system without asserting the exact satellite self-protection mechanism, the complete set of PLE-encoded anti-ICP1 mechanisms, the accession-level natural-host protein, the full functional breadth of divergent NixI homologs, or the experimental scope of the optional NixI__Stix profile. nodes: - node_id: nixi_locus label: NixI locus node_type: GENETIC_ELEMENT description: A NixI-family phage-satellite locus represented by the DefenseFinder NixI__NixI profile. - node_id: icp1_genome_cleavage label: ICP1 genome cleavage node_type: BIOLOGICAL_PROCESS description: NixI-dependent cleavage of the ICP1 bacteriophage genome in PLE-positive Vibrio cholerae. - node_id: icp1_replication_inhibition label: ICP1 replication inhibition node_type: BIOLOGICAL_PROCESS description: Inhibition of ICP1 genome replication and progeny production by NixI. - node_id: nixi_system_trait label: NixI system node_type: TRAIT grounding: traitmech:000333 description: Possession of a genome-encoded NixI 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: nixi_locus predicate: contributes to predicate_id: RO:0002326 object: icp1_genome_cleavage description: The PLE-encoded NixI nicking endonuclease is necessary for cleavage of ICP1 DNA in vivo, and DefenseFinder models NixI with the mandatory NixI__NixI profile. evidence: - reference: DOI:10.1093/nar/gkac002 snippet: Together, these data show that PLE encodes a nicking endonuclease, NixI, that is necessary for cleavage of ICP1’s genome in vivo and that shows in vitro specificity for sequences found in ICP1’s genome notes: LeGault et al. support NixI as the PLE-encoded nicking endonuclease responsible for ICP1 genome cleavage. - reference: https://raw.githubusercontent.com/mdmparis/defense-finder-models/afb0e5a8b466be53586b13266f5d38d98c3ac268/DefenseFinder_rules.tsv snippet: "NixI\tNixI\t1\t1\tNixI__NixI\tNixI__Stix\t\t" notes: The DefenseFinder rules table models NixI with the NixI__NixI profile as its mandatory component and an optional NixI__Stix profile. - reference: https://raw.githubusercontent.com/mdmparis/defense-finder-models/afb0e5a8b466be53586b13266f5d38d98c3ac268/Liste_hmm_system.md snippet: '| NixI__NixI | NixI__NixI | NixI | Custom | 20 |' notes: The DefenseFinder HMM inventory records NixI__NixI under the NixI model namespace. - subject: nixi_locus predicate: contributes to predicate_id: RO:0002326 object: icp1_replication_inhibition description: NixI inhibits ICP1 replication and decreases ICP1 virion production. evidence: - reference: DOI:10.1093/nar/gkac002 snippet: Together, these data demonstrate that nixI is a potent inhibitor of ICP1 replication, resulting in decreased virion production. notes: LeGault et al. show that NixI is a potent inhibitor of ICP1 replication. - reference: DOI:10.1093/nar/gkac002 snippet: NixI, however, is sufficient to limit ICP1 progeny production in a single round of infection notes: LeGault et al. show that NixI is sufficient to limit ICP1 progeny production. - subject: icp1_genome_cleavage predicate: contributes to predicate_id: RO:0002326 object: icp1_replication_inhibition description: NixI-dependent cleavage of the ICP1 genome contributes to inhibition of ICP1 replication. evidence: - reference: DOI:10.1093/nar/gkac002 snippet: Here, we characterize a PLE-encoded nuclease, NixI, that blocks phage development likely by nicking ICP1’s genome as it transitions to RCR notes: LeGault et al. connect NixI's nicking of ICP1 DNA to blocked phage development during the transition to rolling-circle replication. - reference: DOI:10.1093/nar/gkac002 snippet: Together, these data show that PLE encodes a nicking endonuclease, NixI, that is necessary for cleavage of ICP1’s genome in vivo and that shows in vitro specificity for sequences found in ICP1’s genome notes: LeGault et al. support NixI as the PLE-encoded nicking endonuclease responsible for ICP1 genome cleavage. - subject: icp1_replication_inhibition predicate: confers predicate_id: METPO:2007700 object: nixi_system_trait description: NixI-dependent ICP1 replication inhibition realizes the NixI system trait. evidence: - reference: DOI:10.1093/nar/gkac002 snippet: Here, we characterize a PLE-encoded nuclease, NixI, that blocks phage development likely by nicking ICP1’s genome as it transitions to RCR notes: LeGault et al. characterize NixI as a PLE-encoded nuclease blocking ICP1 phage development. - reference: https://raw.githubusercontent.com/mdmparis/defense-finder-models/afb0e5a8b466be53586b13266f5d38d98c3ac268/List_system_article.md snippet: NixI | 10\.1101/2021\.07\.12\.452122 | A phage parasite deploys a nicking nuclease effector to inhibit replication of its viral host notes: The DefenseFinder article registry maps the named NixI model namespace to the LeGault et al. PLE-encoded nicking-nuclease preprint, later published under DOI:10.1093/nar/gkac002. - subject: nixi_system_trait predicate: is a predicate_id: rdfs:subClassOf object: phage_defense_system description: NixI system possession is a phage-defense-system trait. evidence: - reference: DOI:10.1093/nar/gkac002 snippet: Phage parasites can be considered host defense systems, as the parasite inhibits production of its viral host, benefiting the bacterial population notes: LeGault et al. place phage parasites such as NixI-encoding PLE among host defense systems because they inhibit their viral hosts. discussions: - discussion_id: nixi-stix-and-satellite-scope-gap prompt: Resolve NixI satellite self-protection, optional Stix profile scope, natural-host protein accessions, and divergent-homolog activity before minting narrower NixI mechanism children. kind: KNOWLEDGE_GAP status: OPEN rationale: LeGault et al. support NixI as a PLE-encoded nicking endonuclease that cleaves ICP1 DNA and inhibits ICP1 genome replication, and DefenseFinder models NixI with a required NixI__NixI profile plus optional NixI__Stix. This first system-level record leaves the exact PLE self-protection mechanism, the optional Stix profile's experimental scope, the accession-level PLE1 NixI protein, the breadth of divergent homolog activity, and additional PLE anti-ICP1 mechanisms unresolved. attaches_to: - causal_graphs#nixi_locus_inhibits_icp1_replication posed_by: codex posed_date: '2026-09-21' curation_history: - timestamp: '2026-09-21T10:01:24Z' curator: codex action: MINTED_TRAITMECH_ID changes: Minted NixI system as a DOI-backed GENOMICS TraitRecord under phage defense system after an ignored-and-hidden duplicate review found no exact live TraitMech, METPO, history, or prior proposal record; the replacement placeholder is reserved in proposals/metpo_traitmech_v210. llm_assisted: true - timestamp: '2026-09-21T10:30:48Z' curator: codex action: UPDATED_CAUSAL_GRAPH changes: 'Connected ICP1 genome cleavage to ICP1 replication inhibition in the NixI graph so nuclease-mediated DNA cleavage lies on the path from NixI locus to NixI system, addressing issue #1189.' llm_assisted: true