trans-lesion synthesis past bulky benzo[a]pyrene diol epoxide N²-dG and N⁶-dA lesions catalyzed by DNA bypass polymerases

The effectiveness of in vitro primer elongation reactions catalyzed by human bypass DNA polymerases κ (hDinB1), pol η (hRad30A), pol ι (hRad30B), and yeast pol ζ (Rev3 and Rev7) in site-specifically modified template oligonucleotide strands were studied in vitro. The templates contained single bulky lesions derived from the trans-addition of the mutagenic (+)- or (-)-enantiomers of r7,t8-dihydroxy-t9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (a metabolite of the environmental carcinogen benzo[a]pyrene), to the exocyclic amino groups of guanine or adenine in oligonucleotide templates 33, or more, bases long. In "running start" primer extension reactions, pol κ effectively bypassed both the stereoisomeric (+)- and (-)-trans-guanine adducts but not the analogous adenine adducts. In sharp contrast, pol η, which exhibits considerable sequence homology with pol κ (both belong to the group of Y family polymerases), is partially blocked by the guanine adducts and the (-)-trans-adenine adduct, although the stereoisomeric (+)-trans-adenine adduct is more successfully bypassed. Neither pol ι nor pol ζ, either alone or in combination, were effective in trans-lesion synthesis past the same adducts. In all cases, the fidelity of insertion is dependent on adduct stereochemistry and structure. Generally, error-free nucleotide insertion opposite the lesions tends to depend more on adduct stereochemistry than error-prone insertion. None of the polymerases tested are a universal bypass polymerase for the stereoisomeric bulky polycyclic aromatic hydrocarbon-DNA adducts derived from anti-BPDE.