The in vivo characterization of translesion synthesis across UV-induced lesions in Saccharomyces cerevisiae: Novel insights into Pol and Pol dependent frameshift mutagenesis

UV irradiation, a known carcinogen, induces the formation of dipyrimidine dimers with the predominant lesions being cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone adducts (6-4PPs). The relative roles of the yeast translesion synthesis DNA polymerases Pol and Pol in UV survival and mutagenesis were examined using strains deficient in one or both polymerases. In addition, photoreactivation was used to specifically remove CPDs, thus allowing an estimate to be made of the relative contributions of CPDs versus 6-4PPs to overall survival and mutagenesis. In terms of UV-induced mutagenesis, we focused on the +1 frameshift mutations detected by reversion of the lys2A746 allele, as Pol produces a distinct mutational signature in this assay. Results suggest that CPDs are responsible for most of the UV-associated toxicity as well as for the majority of UV-induced frameshift mutations in yeast. Although the presence of Pol generally suppresses UV-induced mutagenesis, our data suggest a role for this polymerase in generating some classes of +1 frameshifts. Finally, the examination of frameshift reversion spectra indicates a hierarchy between Pol and Pol with respect to the bypass of UV-induced lesions.

Key Words: Pol eta, Pol zeta, Translesion synthesis, UV irradiation, yeast

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