CATALYSIS OF HOMOLOGOUS DNA PAIRING BY YEAST RAD51 AND RAD54 PROTEINS

The Saccharomyces cerevisiae RAD51 and RAD54 genes are both required f or the occurrence of homologous recombination and for the repair of do uble-stranded DNA breaks(1). Previous studies have indicated that Rad5 1 protein, together with the single-stranded DNA-binding factor replic ation protein A (RPA), can promote the formation of heteroduplex DNA(2 -4), which is a key intermediate in homologous recombination(1), Here we report the purification of the Rad54 protein to near homogeneity an d the biochemical testing of its molecular function. We find that Rad5 4 protein possesses a double-stranded DNA-dependent ATPase activity, a nd GRAPHICS that it interacts with the Rad51 protein. Addition of Rad5 4 protein to reactions containing Rad51 strongly stimulates the rate o f pairing between homologous single-stranded and double-stranded DNA m olecules. We conclude that Rad54 acts to overcome kinetic impediments that would limit homologous DNA pairing between recombining chromosome s in vivo.