Genome instability in RAD54 mutants of Saccharomyces cerevisiae

The RAD54 gene of Saccharomyces cerevisiae encodes a conserved dsDNA-dependent ATPase of the Swi2/Snf2 family with a specialized function during recombinational DNA repair. Here we ana-lyzed the consequences of the loss of Rad54 func-tion in vegetative (mitotic) cells. Mutants in RAD54 exhibited drastically reduced rates of spontaneous intragenic recombination but were pro®cient for spontaneous intergenic recombinant formation. The intergenic recombinants likely arose by a RAD54-independent pathway of break-induced replication. Signi®cantly increased rates of spontaneous chromosome loss for diploid rad54/rad54 cells were identi®ed in several independent assays. Inter-estingly, the increase in chromosome loss appeared to depend on the presence of a homolog. In addition, the rate of complex genetic events involv-ing chromosome loss were drastically increased in diploid rad54/rad54 cells. Together, these data suggest a role for Rad54 protein in the repair of spontaneous damage, where in the absence of Rad54 protein, homologous recombination is initi-ated but not properly terminated, leading to misre-pair and chromosome loss