REPAIR OF GAMMA RAY-INDUCED S1 NUCLEASE HYPERSENSITIVE SITES IN YEAST DEPENDS ON HOMOLOGOUS MITOTIC RECOMBINATION AND A RAD18-DEPENDENT FUNCTION

Repair under non-growth conditions of DNA double-strand breaks (DSB) and chromatin sites sensitive to S1 endonuclease (SSS) induced by Cobalt-60-gamma rays were monitored in repair-competent and deficient strains of Saccharomyces cerevisiae by pulsed field gel-electrophoresis. In stationary-phase cells of a repair-competent RAD diploid, and an excision-deficient rad3-2 diploid, SSS are repaired as efficiently as DSB, whereas in a repair-competent RAD haploid, and a rad 50-1 diploid, neither SSS nor DSB are repaired. The rad18-2 diploid repairs DSB well but is defective in SSS repair. Obviously, SSS repair in yeast chromatin, like DSB repair, depends on recombination, but unlike DSB repair depends additionally on RAD18 function.