RAD9, RAD17, AND RAD24 ARE REQUIRED FOR S-PHASE REGULATION IN SACCHAROMYCES-CEREVISIAE IN RESPONSE TO DNA-DAMAGE

We have previously shown that a checkpoint dependent on MEC1 and RAD53 slows the rate of S phase progression in Saccharomyces cerevisae in r esponse to alkylation damage. Whereas wild-type cells exhibit a slow S phase in response to damage, mec1-1 and rad53 mutants replicate rapid ly in the presence or absence of DNA damage. In this report, we show t hat other genes (RAD9, RAD17, RAD24) involved in the DNA damage checkp oint pathway also play a role in regulating S phase in response to DNA damage. Furthermore, RAD9, RAD17, and RAD24 fall into two groups with respect to both sensitivity to alkylation and regulation of S phase. We also demonstrate that the more dramatic defect in S phase regulatio n in the mec1-1 and rad 53 mutants is epistatic to a less severe defec t seen in rad9 Delta, rad17 Delta, and rad24 Delta. Furthermore, the t riple rad9 Delta rad17 Delta rad24 Delta mutant also has a less severe defect than mec1-1 or rad53 mutants. Finally, we demonstrate the spec ificity of this phenotype by showing that the DNA repair and/or checkp oints mutants mgt1 Delta, mag1 Delta, apn1 Delta, rev3 Delta, rad18 De lta, rad16 Delta, dun1-Delta 100, sad4-1 Delta, tel1 Delta, rad26 Delt a, rad51 Delta, rad52-1 Delta, rad54 Delta, rad14 Delta, rad1 Delta, p ol30-46, pol30-52, mad3 Delta, pds1 Delta/esp2 Delta, pms1 Delta, mlh1 Delta, and msh2 Delta are all proficient at S phase regulation, even though some of these mutations confer sensitivity to alkylation.