Yeast DNA Polymerase ζ Is an Efficient Extender of Primer Ends Opposite from 7,8-Dihydro-8-Oxoguanine and O(6)-Methylguanine

Genetic studies in Saccharomyces cerevisiae have indicated the requirement of DNA polymerase (Pol) ζ for mutagenesis induced by UV light and by other DNA damaging agents. However, on its own, Polζ is highly inefficient at replicating through DNA lesions; rather, it promotes their mutagenic bypass by extending from the nucleotide inserted opposite the lesion by another DNA polymerase. So far, such a role for Polζ has been established for cyclobutane pyrimidine dimers, (6-4) dipyrimidine photoproducts, and abasic sites. Here, we examine whether Polζ can replicate through the 7,8-dihydro-8-oxoguanine (8-oxoG) and O(6)-methylguanine (m6G) lesions. We chose these two lesions for this study because the replicative polymerase, Polδ, can replicate through them, albeit weakly. We found that Polζ is very inefficient at inserting nucleotides opposite both these lesions, but it can efficiently extend from the nucleotides inserted opposite them by Polδ. Also, the most efficient bypass of 8-oxoG and m6G lesions occurs when Polδ is combined with Polζ, indicating a role for Polζ in extending from the nucleotides inserted opposite these lesions by Polδ. Thus, Polζ is a highly specialized polymerase that can proficiently extend from the primer ends opposite DNA lesions, irrespective of their degree of geometric distortion. Polζ, however, is unusually sensitive to geometric distortion of the templating residue, as it is highly inefficient at incorporating nucleotides even opposite the moderately distorting 8-oxoG and m6G lesions.