Loss of Pol32, a subunit of DNA polymerases δ and ζ, leads to different patterns of genome stability than direct impairment of these individual polymerases

Pol32 is a subunit shared by DNA polymerases δ and ζ, yet its role in maintaining genome integrity remains incompletely defined. Here, we employed whole-genome sequencing of mutation-accumulation lines to systematically characterize the genome-wide effects of a POL32 deletion in diploid Saccharomyces cerevisiae. Loss of Pol32 led to substantially (>5-fold) elevated rates of loss of heterozygosity (LOH), chromosome rearrangements, and aneuploidy, but resulted in substantially less genome instability than observed in strains with low levels of DNA polymerase δ. In particular, there was only a small (pol32 mutation on mutation rates. Notably, a prominent hotspot for chromosome rearrangements located near the end of chromosome VII was observed in pol32 strains. Although deletion of REV3 (encoding the catalytic subunit of Pol ζ) had no significant effect on genome integrity in a wild-type background, pol32 rev3 double mutants had reduced rates of most types of chromosome alterations compared to the pol32 single mutant, implicating Pol ζ in driving the genome instability induced by the Pol32 deficiency. Together, these findings provide new insights into how a shared structural subunit of several DNA polymerases contributes to the regulation of genome stability.IMPORTANCEPol32 is a subunit of DNA polymerases δ (an essential replicative enzyme) and ζ (an error-prone DNA polymerase required for DNA repair). We show that yeast strains that lack this protein have elevated rates of mitotic recombination, large deletions/duplications, translocations, and other types of genomic alterations. The high level of genomic alterations in pol32 mutants is substantially suppressed in strains that lack DNA polymerase ζ, suggesting that this error-prone polymerase may stimulate DNA breaks in conditions of DNA replication stress. Our studies are likely to have wide relevance since sequence variants of POLD3 (the human homolog of Pol32) are associated with certain types of human tumors.