Molecular dissection of interactions between Rad51 and members of the recombination-repair group

Recombination is important for the repair of DNA damage and for chromosome segregation during meiosis; it has also been shown to participate in the re gulation of cell proliferation. In the yeast Saccharomyces cerevisiae, reco mbination requires products of the RAD52 epistasis group. The Rad51 protein associates with the Rad51, Rad52, Rad54, and Rad55 proteins to form a dyna mic complex, We describe a new strategy to screen for mutations which cause specific disruption of the interaction between certain proteins in the com plex, leaving other interactions intact. This approach defines distinct pro tein interaction domains and protein relationships within the Rad51 complex . Alignment of the mutations onto the constructed three-dimensional model o f the Rad51 protein reveal possible partially overlapping interfaces for th e Rad51-Rad52 and the Rad51-Rad54 interactions. Rad51-Rad55 and Rad51-Rad51 interactions are affected by the same spectrum of mutations, indicating si milarity between the two modes of binding. Finally, the detection of a subs et of mutations within Rad51 which disrupt the interaction with mutant Rad5 2 protein but activate the interaction with Rad54 suggests that dynamic cha nges within the Rad51 protein may contribute to an ordered reaction process .