The relative roles in vivo of Saccharomyces cerevisiae Pol [eta], Pol [zeta], 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

We have investigated the relative roles in vivo of Saccharomyces cerevisiae DNA polymerase [eta], DNA polymerase [zeta], Rev1 protein, and the DNA polymerase [delta] 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 [eta] 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 [zeta], rather than DNA polymerase [delta] as previously suggested, is responsible for insertion in bypass events other than those in which polymerase [eta] performs this function. However, DNA polymerase [delta] 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 [zeta] or Rev1. In contrast, bypass of the T-T dimer in the pol32[DELTA] strain occurs at the wild-type frequency.