HOMOTYPIC AND HETEROTYPIC PROTEIN ASSOCIATIONS CONTROL RAD51 FUNCTIONIN DOUBLE-STRAND BREAK REPAIR

Rad51 is essential for efficient repair of DNA double-strand breaks (D SBs) and recombination in Saccharomyces cerevisiae. Here, we examine R ad51 protein-protein interactions and their biological significance. G AL4 two-hybrid fusion analysis demonstrated that the amino-terminal re gion of Rad51 mediates both a strong Rad51:Rad51 self-association and a Rad51:Rad52 interaction. Several Rad51 variants were characterized t hat imparted DSB repair defects; these defects appear to result from R ad51 protein-protein interactions. First, a rad51 allele bearing a mis sense mutation in the consensus ATP-binding sequence disrupted DSB rep air in wild-type yeast. The effect of this allele was dependent on the presence of wild-type Rad51 because MMS sensitivity of rad51 Delta st rains were not increased by its expression. Second, we identified a hi ghly conserved RAD51 homolog from Kluyveromyces lactis (KlRAD51) that only partially complemented rad51 Delta strains and impaired DSB repai r in wild-type S. cerevisiae. Third, fusions of Gal4 domains to Rad51 disrupted DSB repair in a manner that required the presence of either Rad51 or Rad52. Because K. lactis RAD51 and RAD52 did not complement a S. cerevisiae rad51 Delta rad52 Delta strain, Rad51-Rad52 functions a ppear to be mediated through additional components. Thus, multiple typ es of Rad51 protein interactions, including self-association, appear t o be important for DSB repair.