DIFFERENT EFFECTS OF RAD GENES OF SACCHAROMYCES CEREVISIAE ON INCISIONS OF INTERSTRAND CROSSLINKS AND MONOADDUCTS IN DNA INDUCED BY PSORALEN PLUS NEAR UV LIGHT TREATMENT

Abstract— The RAD1, RAD2, RAD3 and RAD4 genes of Saccharomyces cerevisiae are required for incising DNA containing UV induced pyrimidine dimers or psoralen plus 360 nm light induced interstrand crosslinks. We have now determined if these genes are also required for incising DNA at psoralen plus 360 nm light induced monoadducts. For distinguishing between incision breaks occurring at crosslinks and at monoadducts. we have used the cdc9‐2 mutant, defective in DNA ligase activity at the restrictive temperature, and the radl‐2 cdc9‐2, rad2‐5 cdc9‐2, rad3‐2 cdc9‐2 and rad4‐4 cdc9‐2 double mutant combinations. We conclude that the radl, rad2, and rad4 mutants are defective in incising DNA both at crosslinks and monoadducts, whereas the rad3 mutant is proficient in incising DNA at monoadducts but not at crosslinks.