The budding yeast Shu complex, a heterotetramer of Shu1, Shu2, Csm2, and Psy3, is important for homologous recombination (HR)-mediated chromosome damage repair and was first characterized a decade ago as promoting Rad51-dependent HR in response to replicative stress, but its mechanistic function and conservation in eukaryotes has remained unknown. Here we provide evidence that the Shu complex is evolutionarily conserved throughout eukaryotes, where it is comprised of a clear Shu2 orthologue physically associating with Rad51 paralogues. The Shu complex itself physically interacts with the rest of the HR machinery during DNA damage repair. Finally, we uncover that the mechanistic function of the Shu complex as a stimulatory co-factor of Rad51 filament formation in vitro, likely explaining the in vivo function of the eukaryotic Shu complex in suppressing error-prone repair. Moving forward, our findings provide a framework for studying the function of the human Shu complex, which will have broad importance in our understanding of DNA damage repair
