Abstract
Saccharomyces cells with a single unrepaired double-strand break adapt after checkpoint-mediated G2/M arrest. We have found that both Rad51 and Rad52 recombination proteins play key roles in adaptation. Cells lacking Rad51p fail to adapt, but deleting RAD52 suppresses rad51Δ. rad52Δ also suppresses adaptation defects of srs2Δ mutants but not those of yku70Δ or tid1Δ mutants. Neither rad54Δ nor rad55Δ affects adaptation. A Rad51 mutant that fails to interact with Rad52p is adaptation defective; conversely, a C-terminal truncation mutant of Rad52p, impaired in interaction with Rad51p, is also adaptation defective. In contrast, rad51-K191A, a mutation that abolishes recombination and results in a protein that does not bind to single-stranded DNA (ssDNA), supports adaptation, as do Rad51 mutants impaired in interaction with Rad54p or Rad55p. An rfa1-t11 mutation in the ssDNA binding complex RPA partially restores adaptation in rad51Δ mutants and fully restores adaptation in yku70Δ and tid1Δ mutants. Surprisingly, although neither rfa1-t11 nor rad52Δ mutants are adaptation defective, the rad52Δ rfa1-t11 double mutant fails to adapt and exhibits the persistent hyperphosphorylation of the DNA damage checkpoint protein Rad53 after HO induction. We suggest that monitoring of the extent of DNA damage depends on independent binding of RPA and Rad52p to ssDNA, with Rad52p's activity modulated by Rad51p whereas RPA's action depends on Tid1p.