The Relative Roles in Vivo of Saccharomyces cerevisiae Pol η, Pol ζ, Rev1 Protein and Pol32 in the Bypass and Mutation Induction of an Abasic Site, T-T (6-4) Photoadduct and T-T cis-syn Cyclobutane Dimer

Abstract

We have investigated the relative roles in vivo of Saccharomyces cerevisiae DNA polymerase η, DNA polymerase ζ, Rev1 protein, and the DNA polymerase δ subunit, Pol32, in the bypass of an abasic site, T-T (6-4) photoadduct and T-T cis-syn cyclobutane dimer, by transforming strains deleted for RAD30, REV3, REV1, or POL32 with duplex plasmids carrying one of these DNA lesions located within a 28-nucleotide single-stranded region. DNA polymerase η was found to be involved only rarely in the bypass of the T-T (6-4) photoadduct or the abasic sites in the sequence context used, although, as expected, it was solely responsible for the bypass of the T-T dimer. We argue that DNA polymerase ζ, rather than DNA polymerase δ as previously suggested, is responsible for insertion in bypass events other than those in which polymerase η performs this function. However, DNA polymerase δ is involved indirectly in mutagenesis, since the strain lacking its Pol32 subunit, known to be deficient in mutagenesis, shows as little bypass of the T-T (6-4) photoadduct or the abasic sites as those deficient in Pol ζ or Rev1. In contrast, bypass of the T-T dimer in the pol32Δ strain occurs at the wild-type frequency.