Translesion synthesis by human DNA polymerase kappa on a DNA template containing a single stereoisomer of dG-(+)- or dG-(-)-anti-N(2)-BPDE (7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene).


Several recently discovered human DNA polymerases are associated with translesion synthesis past DNA adducts. These include human DNA polymerase kappa (pol kappa), a homologue of Escherichia coli pol IV, which enhances the frequency of spontaneous mutation. Using a truncated form of pol kappa (pol kappa Delta C), translesion synthesis past dG-(+)- or dG-(-)-anti-N(2)-BPDE (7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene) adducts was explored. Site-specifically-modified oligodeoxynucleotides containing a single stereoisomeric dG-N(2)-BPDE lesion were used as DNA templates for primer extension reactions catalyzed by pol kappa Delta C. Primer extension was retarded one base prior to the dG-N(2)-BPDE lesion; when incubated for longer times or with higher concentration of enzyme, full primer extension was observed. Quantitative analysis of fully extended products showed preferential incorporation of dCMP, the correct base, opposite all four stereoisomeric dG-N(2)-BPDE lesions. (+)-trans-dG-N(2)-BPDE, a major BPDE-DNA adduct, promoted small amounts of dTMP, dAMP, and dGMP misincorporation opposite the lesion (total 2.7% of the starting primers) and deletions (1.1%). Although (+)-cis-dG-N(2)-BPDE was most effective in blocking translesion synthesis, its miscoding properties were similar to other dG-N(2)-BPDE isomers. Steady-state kinetic data indicate that dCMP is efficiently inserted opposite all dG-N(2)-BPDE adducts and extended past these lesions. The relative frequency of translesion synthesis (F(ins) x F(ext)) of dC.dG-N(2)-BPDE pairs was 2-6 orders of magnitude higher than that of other mismatched pairs. Pol kappa may play an important role in translesion synthesis by incorporating preferentially the correct base opposite dG-N(2)-BPDE. Its relatively low contribution to mutagenicity suggests that other newly discovered DNA polymerase(s) may be involved in mutagenic events attributed to dG-N(2)-BPDE adducts in human cells.




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