Thepol3-tHyperrecombination Phenotype and DNA Damage-Induced Recombination inSaccharomyces cerevisiaeIsRAD50Dependent

Abstract

The DNA polymeraseδ(POL3/CDC2) allelepol3-tofSaccharomyces cerevisiaehas previously been shown to be sensitive to methylmethanesulfonate (MMS) and has been proposed to be involved in base excision repair. Our results, however, show that thepol3-tmutation is synergistic for MMS sensitivity withMAG1, a known base excision repair gene, but it is epistatic withrad50Δ, suggesting thatPOL3may be involved not only in base excision repair but also in a RAD50 dependent function. We further studied the interaction ofpol3-twithrad50Δby examining their effect on spontaneous, MMS-, UV-, and ionizing radiation-induced intrachromosomal recombination. We found thatrad50Δcompletely abolishes the elevated spontaneous frequency of intrachromosomal recombination in thepol3-tmutant and significantly decreases UV- and MMS-induced recombination in bothPOL3andpol3-tstrains. Interestingly,rad50Δhad no effect onγ-ray-induced recombination in both backgrounds between 0 and 50 Gy. Finally, the deletion ofRAD50had no effect on the elevated frequency of homologous integration conferred by thepol3-tmutation.RAD50is possibly involved in resolution of replication forks that are stalled by mutagen-induced external DNA damage, or internal DNA damage produced by growing thepol3-tmutant at the restrictive temperature.