The yeast recombinational repair protein Rad59 interacts with Rad52 and stimulates single-strand annealing

The yeast RAD52 gene is essential for homology-dependent repair of DNA doub le-strand breaks. In vitro, Rad52 binds to single- and double-stranded DNA and promotes annealing of complementary single-stranded DNA. Genetic studie s indicate that the Rad52 and Rad59 proteins act in the same recombination pathway either as a complex or through overlapping functions. Here we demon strate physical interaction between Rad52 and Rad59 using the yeast two-hyb rid system and co-immunoprecipitation from yeast extracts. Purified Rad59 e fficiently anneals complementary oligonucleotides and is able to overcome t he inhibition to annealing imposed by replication protein A (R-PA). Althoug h Rad59 has strand-annealing activity by itself in vitro, this activity is insufficient to promote strand annealing in vivo in the absence of Rad52. T he rfa1-D288Y allele partially suppresses the in vivo strand-annealing defe ct of rad52 mutants, but this is independent of RAD59. These results sugges t that in vivo Rad59 is unable to compete with RPA for single-stranded DNA and therefore is unable to promote single-strand annealing. Instead, Rad59 appears to augment the activity of Rad52 in strand annealing.