Pol32, a Subunit of Saccharomyces cerevisiae DNA Polymerase δ, Suppresses Genomic Deletions and Is Involved in the Mutagenic Bypass Pathway

Abstract

Abstract The Pol32 subunit of S. cerevisiae DNA polymerase (Pol) δ plays an important role in replication and mutagenesis. Here, by measuring the CAN1 forward mutation rate, we found that either POL32 or REV3 (which encodes the Pol ζ catalytic subunit) inactivation produces overlapping antimutator effects against rad mutators belonging to three epistasis groups. In contrast, the msh2Δ pol32Δ double mutant exhibits a synergistic mutator phenotype. Canr mutation spectrum analysis of pol32Δ strains revealed a substantial increase in the frequency of deletions and duplications (primarily deletions) of sequences flanked by short direct repeats, which appears to be RAD52 and RAD10 independent. To better understand the pol32Δ and rev3Δ antimutator effects in rad backgrounds and the pol32Δ mutator effect in a msh2Δ background, we determined Canr mutation spectra for rad5Δ, rad5Δ pol32Δ, rad5Δ rev3Δ, msh2Δ, msh2Δ pol32Δ, and msh2Δ rev3Δ strains. Both rad5Δ pol32Δ and rad5Δ rev3Δ mutants exhibit a reduction in frameshifts and base substitutions, attributable to antimutator effects conferred by the pol32Δ and rev3Δ mutations. In contrast, an increase in these two types of alterations is attributable to a synergistic mutator effect between the pol32Δ and msh2Δ mutations. Taken together, these observations indicate that Pol32 is important in ensuring genome stability and in mutagenesis.