identifier: traitmech:000241 label: Hna system definition: A phage defense system in which an organism possesses an Hna locus encoding a single SF2 helicase/nuclease effector that protects cells from bacteriophage infection by responding to phage single-stranded DNA-binding protein challenge, shifting toward dysregulated nuclease activation, and triggering abortive infection. definition_source: DOI:10.1016/j.chom.2023.01.010 trait_category: GENOMICS term_kind: CLASS mapping_status: PROPOSED parent_traits: - traitmech:000209 synonyms: - synonym_text: Hna anti-phage defense system synonym_type: EXACT_SYNONYM source: DOI:10.1038/s41467-026-73157-2 evidence: - reference: DOI:10.1016/j.chom.2023.01.010 snippet: single phage defense protein, Hna, that provides protection against diverse phages in Sinorhizobium meliloti notes: Sather et al. support Hna as a single-protein phage-defense determinant in S. meliloti. - reference: DOI:10.1016/j.chom.2023.01.010 snippet: Homologs of Hna are distributed widely across bacterial lineages notes: Sather et al. support placing Hna at a bacterial family level rather than curating only the S. meliloti instance. - reference: DOI:10.1016/j.chom.2023.01.010 snippet: Hna contains superfamily II helicase motifs at its N terminus and a nuclease motif at its C terminus, with mutagenesis of these motifs inactivating viral defense notes: Sather et al. connect the predicted helicase/nuclease domain architecture to Hna antiphage activity. - reference: DOI:10.1038/s41467-026-73157-2 snippet: Hna is a broadly distributed anti-phage immune system that confers resistance against diverse phage by eliciting an abortive infection response notes: Hooper et al. independently support Hna as a named anti-phage immune system with abortive-infection output. - reference: DOI:10.1038/s41467-026-73157-2 snippet: shifts catalytic partitioning toward dysregulated nuclease activation notes: Hooper et al. support phage single-stranded DNA-binding protein as a direct stimulus for Hna nuclease activation. - reference: DOI:10.1016/j.chom.2023.01.010 snippet: Hna limits phage spread by initiating abortive infection in response to a phage protein notes: Sather et al. support abortive infection in response to a phage-encoded protein as the Hna phage-defense output. canonical_examples: - taxon_id: NCBITaxon:382 taxon_label: Sinorhizobium meliloti note: Sather et al. showed that Sinorhizobium meliloti Hna provides protection against diverse bacteriophages and triggers abortive infection in phage-infected cells. reference: DOI:10.1016/j.chom.2023.01.010 causal_graphs: - graph_id: hna_ssb_triggered_abortive_infection title: Hna nuclease activation couples phage SSB challenge to abortive infection description: Evidence-backed process sketch linking an Hna locus to phage single-stranded DNA-binding protein challenge, dysregulated helicase/nuclease activity, abortive infection, and inhibition of phage spread. scope_status: NONMECHANISTIC scope_notes: The graph captures Sather et al. and Hooper et al. Hna phage-SSB-triggered abortive infection evidence without asserting one universal phage trigger, escape route, DNA substrate, ATP-concentration gate, or host-cell-death timing across all Hna homologs. nodes: - node_id: hna_locus label: Hna locus node_type: GENETIC_ELEMENT description: A single-effector Hna phage-defense locus encoding an SF2 helicase/nuclease immune protein. - node_id: phage_ssb_stimulation label: phage SSB stimulation node_type: BIOLOGICAL_PROCESS description: Stimulation of Hna by a phage-encoded single-stranded DNA-binding protein. - node_id: hna_nuclease_activation label: Hna nuclease activation node_type: MOLECULAR_FUNCTION description: Dysregulated activation of Hna nuclease activity after phage single-stranded DNA-binding protein challenge. - node_id: abortive_infection_response label: abortive infection response node_type: BIOLOGICAL_PROCESS description: Host cell death after infection that prevents release of bacteriophage progeny. - node_id: hna_system_trait label: Hna system node_type: TRAIT grounding: traitmech:000241 description: Possession of a genome-encoded Hna 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: hna_locus predicate: contributes to predicate_id: RO:0002326 object: hna_nuclease_activation description: Hna loci encode SF2 helicase/nuclease proteins whose conserved helicase and nuclease motifs are required for viral defense. evidence: - reference: DOI:10.1016/j.chom.2023.01.010 snippet: mutagenesis of these motifs inactivating viral defense notes: Sather et al. connect Hna helicase and nuclease motifs to antiphage activity. - subject: phage_ssb_stimulation predicate: activates predicate_id: RO:0002213 object: hna_nuclease_activation description: A phage-encoded single-stranded DNA-binding protein stimulates Hna and shifts it toward dysregulated nuclease activation. evidence: - reference: DOI:10.1016/j.chom.2023.01.010 snippet: A similar host cell response is triggered in cells containing Hna upon expression of a phage-encoded single-stranded DNA binding protein (SSB) notes: Sather et al. support Hna response to a phage SSB independently of whole-phage infection. - reference: DOI:10.1038/s41467-026-73157-2 snippet: shifts catalytic partitioning toward dysregulated nuclease activation notes: Hooper et al. directly connect phage SSB stimulation to Hna nuclease activation. - subject: hna_nuclease_activation predicate: contributes to predicate_id: RO:0002326 object: abortive_infection_response description: Dysregulated Hna nuclease activation damages DNA, causes cellular toxicity, and contributes to the abortive infection response. evidence: - reference: DOI:10.1038/s41467-026-73157-2 snippet: Disruption of this balance enhances DNA cleavage and causes cellular toxicity notes: Hooper et al. support Hna nuclease dysregulation as a toxic DNA-cleavage output. - reference: DOI:10.1016/j.chom.2023.01.010 snippet: infected cells carrying the system die but do not release phage progeny notes: Sather et al. support the abortive infection host-cell fate of Hna-containing cells. - subject: abortive_infection_response predicate: confers predicate_id: METPO:2007700 object: hna_system_trait description: Hna-mediated abortive infection is the phage-defense output that realizes the Hna system trait. evidence: - reference: DOI:10.1016/j.chom.2023.01.010 snippet: Hna limits phage spread by initiating abortive infection in response to a phage protein notes: Sather et al. support abortive infection as the Hna antiviral output. - subject: hna_system_trait predicate: is a predicate_id: rdfs:subClassOf object: phage_defense_system description: Hna system possession is a phage-defense-system trait. evidence: - reference: DOI:10.1038/s41467-026-73157-2 snippet: Hna is a broadly distributed anti-phage immune system notes: Hooper et al. place Hna in the anti-phage immune-system family. discussions: - discussion_id: hna-trigger-and-family-breadth-gap prompt: Resolve Hna trigger breadth, phage escape routes, and family architecture before minting narrower Hna mechanism children. kind: KNOWLEDGE_GAP status: OPEN rationale: Sather et al. support Sinorhizobium Hna abortive infection after phage infection or phage SSB expression, and Hooper et al. support 5A SSB stimulation of nuclease activation, but Hna homologs need separate review before TraitMech asserts one universal phage trigger, ATP-dependent activation gate, DNA substrate, escape route, or host death timing across the full Hna family. posed_by: codex posed_date: '2026-09-18' curation_history: - timestamp: '2026-09-18T12:46:11Z' curator: codex action: MINTED_TRAITMECH_ID changes: Minted Hna 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_v118. llm_assisted: true