Benzo[a]pyrene diol epoxide-deoxyguanosine adducts are accurately bypassed by yeast DNA polymerase zeta in vitro

The possible role of bypass DNA polymerase zeta in mutagenic translesion synthesis past benzoa]pyrene (BP) 7,8-diol-9,10-epoxide (DE) N(2)-deoxyguanosine (dG) adducts has been examined. We prepared 59-mer DNA templates containing dG adducts derived from trans opening of enantiomers of BP DE-2, in which the 7-hydroxyl group and epoxide oxygen are trans. The 10S-BP DE-dG and 10R-BP DE-dG adducts derive from the (+)- and (-)-DE-2 enantiomers, respectively. The adducted dG is located at a site identified as a G-->T mutational hotspot in random mutagenesis studies of (+)-BP DE-2 in Chinese hamster V-79 cells. Yeast pol zeta (complex of Gst-Rev3p and Rev7p) formed extension products (total of all lengths) of 71, 74 and 88% of a primer annealed to the 10S-BP DE-dG, 10R-BP DE-dG and non-adducted 59-mer templates, respectively. However, only 18 and 19% of the primer was extended to the full-length product on 10S-BP DE-dG and 10R-BP DE-dG adducted templates compared to 55% of the primer on the non-adducted template. A major 34-mer product corresponding to primer elongation up to and including the base before the adduct indicated that nucleotide incorporation opposite both adducts was strongly blocked. Full-length products were isolated from gels and subjected to PCR amplification and cloning. Sequence analysis of more than 300 clones of these full-length products on each template showed that only the correct dCMP was incorporated opposite both the adducted and non-adducted G-hotspot in the template. This corresponds to a probability of mutation lower than 0.3%, the limit of detection, and demonstrates the remarkable fidelity of yeast pol zeta in translesion synthesis past these BP DB-dG lesions in vitro.