BPS2026 – RAD51 paralog complexes template RAD51 filament formation in DNA repair by homologous recombination

Homologous recombination (HR) is a highly conserved DNA repair pathway essential for maintaining genome integrity. A key step in HR is the assembly of the RAD51 recombinase into a filament on single-stranded DNA (ssDNA), a process critically dependent on a family of RAD51 paralogs. Despite their importance as tumor suppressors, the precise mechanisms by which these paralogs orchestrate RAD51 filament formation have remained elusive. Through structural characterization of different yeast and human RAD51 paralog complexes bound to RAD51 and DNA, we reveal that eukaryotes possess a versatile toolkit of paralog architectures, characterized by dynamic “loader” complexes and specialized “anchor” complexes. In all cases, paralog complexes template the nucleation of RAD51 filament, specifically on ssDNA. This intricate molecular choreography is tightly regulated by ATP hydrolysis, which acts as a molecular switch to control the dynamic assembly and timely release of the paralog machinery. Moreover, the first RAD51 protomer itself emerges as a transient yet integral component of the nucleation complex in both yeast and human systems. Our work provides a unifying mechanism for RAD51 paralog function across eukaryotes and delivers an atomic blueprint for interpreting disease-causing mutations.