Swi2/Snf2-related translocases prevent accumulation of toxic Rad51 complexes during mitotic growth.

Purified DNA translocases Rdh54 and Rad54 can dissociate complexes formed by eukaryotic RecA-like recombinases on double-stranded DNA. Here, we show that Rad51 complexes are dissociated by these translocases in mitotic cells. Rad51 overexpression blocked growth of cells deficient in Rdh54 activity. This toxicity was associated with accumulation of Rad51 foci on undamaged chromatin. At normal Rad51 levels, rdh54 deficiency resulted in slight elevation of Rad51 foci. A triple mutant lacking Rdh54, Rad54, and a third Swi2/Snf2 homolog Uls1 accumulated Rad51 foci, grew slowly, and suffered chromosome loss. Thus, Uls1 and Rad54 can partially substitute for Rdh54 in the removal of toxic, nondamage-associated Rad51-DNA complexes. Additional data suggest that the function of Rdh54 and Rad54 in removal of Rad51 foci is significantly specialized; Rad54 predominates for removal of damage-associated foci, and Rdh54 predominates for removal of nondamage-associated foci.