Translesion synthesis by yeast DNA polymerase ζ from templates containing lesions of ultraviolet radiation and acetylaminofluorene

In the yeast Saccharomyces cerevisiae, DNA polymerase zeta (Pol zeta) is required in a major lesion bypass pathway. To help understand the role of Pol zeta in lesion bypass, we have performed in vitro biochemical analyses of this polymerase in response to several DNA lesions. Purified yeast Pol zeta performed limited translesion synthesis opposite a template TT (6-4) photoproduct, incorporating A or T with similar efficiencies land less frequently G) opposite the 3 ' T, and predominantly A opposite the 5 ' T, Purified yeast Pol zeta predominantly incorporated a G opposite an acetylaminofluorene (AAF)-adducted guanine, The lesion, however, significantly inhibited subsequent extension. Furthermore, yeast Pol zeta catalyzed extension DNA synthesis from primers annealed opposite the AAF-guanine and the 3 ' T of the TT (6-4) photoproduct with varying efficiencies. Extension synthesis was more efficient when A or C was opposite the AAF-guanine, and when G was opposite the 3 ' T of the TT (6-4) photoproduct. In contrast, the 3 ' T of a cis-syn TT dimer completely blocked purified yeast Pol zeta, whereas the 5 ' T was readily bypassed. These results support the following dual-function model of Pol zeta. First, Pol zeta catalyzes nucleotide incorporation opposite AAF-guanine and TT (6-4) photoproduct with a limited efficiency. Secondly, more efficient bypass of these lesions may require nucleotide incorporation by other DNA polymerases followed by extension DNA synthesis by Pol zeta.