SWI5

Model summary

A nuclear chromatin-associated assembly factor that organizes homologous recombination repair after DNA damage. It functions as a non-enzymatic scaffold that binds partner proteins to build the recombination mediator complex on damaged chromatin, thereby promoting strand-exchange repair during the cellular response to ionizing radiation. By stabilizing and coordinating repair assemblies, it ensures efficient double-strand break repair within the nucleus.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture: a single, centrally placed Swi5-family module, IPR010760 (DNA repair protein, Swi5 family) spanning residues 59–235.

   This family-defining core occupies the bulk of the polypeptide and is characteristic of non-enzymatic DNA repair adaptors that assemble and regulate homologous recombination machinery. The absence of catalytic motifs and the dominance of a repair-scaffold signature indicate a protein whose primary chemistry is macromolecular assembly rather than enzymatic turnover. Such Swi5-family cores typically form obligate heteromeric complexes and bind partner proteins with high specificity, which causally supports a molecular function centered on GO:0005515 protein binding.

2. 02

   From this scaffolded Swi5 architecture, the molecular function propagates into homologous recombination pathways.

   The Swi5 family is a hallmark of the recombination mediator ensemble that activates and coordinates strand-exchange reactions. This architecture drives assembly of repair complexes that stabilize single-stranded DNA and promote presynaptic filament formation, thereby enforcing GO:0000724 double-strand break repair via homologous recombination. Because ionizing radiation generates DNA double-strand breaks and funnels repair into homologous pathways, a Swi5-centered scaffold naturally operates during the cellular response to ionizing radiation, aligning with GO:0071479 cellular response to ionizing radiation.

3. 03

   Cellular placement follows from function and binding mode.

   Homologous recombination occurs on chromatinized templates; thus a Swi5-family scaffold that organizes recombination assemblies is expected to reside on chromatin and within nuclear repair condensates. This reasoning anchors the protein in GO:0000785 chromatin and in the dedicated GO:0033061 Swi5-Sfr1 complex, the canonical mediator assembly that nucleates HR machinery. The experimentally observed nuclear localization is consistent with this chromatin-bound nuclear complex.

4. 04

   Mechanistically, the Swi5-family core causes formation of a mediator complex that binds and stabilizes HR factors on damaged chromatin.

   I hypothesize that the protein hetero-oligomerizes with its Sfr1 partner to form the Swi5-Sfr1 complex, which then recruits and stimulates downstream HR modules. Likely partners include recombinase loaders and ssDNA-stabilizing factors; through multivalent protein binding, the complex concentrates and activates HR at sites of radiation-induced breaks, ensuring efficient strand invasion and repair completion within the nuclear chromatin environment.