Evidence for a second function for Saccharomyces cerevisiae Rev1p

The function of the Saccharomyces cerevisiae REV1 gene is required for tran slesion replication and mutagenesis induced by a wide variety of DNA-damagi ng agents. We showed previously that Rev1p possesses a deoxycytidyl transfe rase activity, which incorporates dCMP opposite abasic sites in the DNA tem plate, and that dCMP insertion is the major event during bypass of an abasi c site in vivo. However, we now find that Rev1p function is needed for the bypass of a T-T (6-4) UV photoproduct, a process in which dCMP incorporatio n occurs only very rarely, indicating that Rev1p possesses a second functio n. In addition, we find that Rev1p function is, as expected, required for b ypass of an abasic site. However, replication past this lesion was also muc h reduced in the G-193R rev1-1 mutant, which we find retains substantial le vels of deoxycytidyl transferase activity. This mutant is, therefore, presu mably deficient principally in the second, at present poorly defined, funct ion. The bypass of an abasic site and T-T (6-4) lesion also depended on REV 3 function, but neither it nor REV1 was required for replication past the T -T dimer; bypass of this lesion presumably depends on another enzyme.