Human and yeast Rad52 proteins promote DNA strand exchange

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Abstract
Studies of rad52 mutants in Saccharomyces cerevisiae have revealed a critical role of Rad52 protein in double-strand break repair and meiosis, and roles in both RAD51-dependent and -independent pathways of recombination. In vitro, both yeast and human Rad52 proteins play auxiliary roles with RPA in the action of Rad51. Rad52 also has annealing activity and promotes the formation of D-loops in superhelical DNA. The experiments described here show that Homo sapiens (Hs)Rad52 and yeast Rad52 proteins promote strand exchange as well. Strand exchange was promoted by the N-terminal domain of HsRad52 that contains residues 1-237, which includes the residues required to form rings of Rad52, whereas other truncated domains, both N-terminal and C-terminal, were inactive. For both yeast Rad52 and HsRad52, the yield of strand-exchange reactions was proportional to the fractional A.T content of the DNA substrates, but both enzymes catalyzed exchange with substrates that contained up to at least 50% G.C. Observations made on S. cerevisiae Rad52 protein from mutants with severe recombination deficiencies indicate that the strand-exchange activity measured in vitro reflects a biologically significant property of Rad52 protein.