Human DNA polymerases catalyze lesion bypass across benzo[a]pyrene-derived DNA adduct clustered with an abasic site

The combined action of oxidative stress and genotoxic polycyclic aromatic hydrocarbons derivatives can lead to cluster-type DNA damage that includes both a modified nucleotide and a bulky lesion. As an example, we investigated the possibility of repair of an AP site located opposite a minor groove-positioned (+)-trans-BPDE-dG or a base-displaced intercalated (+)-cis-BPDE-dG adduct (BP lesion) by a BER system. Oligonucleotides with single uracil residue in the certain position were annealed with complementary oligonucleotides bearing either a cis- or trans-BP adduct. Digestion with uracil DNA glycosylase was utilized to generate an AP site which was then hydrolyzed by APE1, and the resulting gap was processed by X-family DNA polymerases β (Polβ) and λ (Polλ), or Y-family polymerase β (Polβ). By varying reaction conditions, namely, Mg²⁺/Mn²⁺ replacement/combination and ionic strength decrease, we found that under certain conditions both Polβ and Polι can catalyze lesion bypass across both cis- and trans-BP adducts in the presence of physiological dNTP concentrations. Polβ and Polι catalyze gap filling trans-lesion synthesis in an error prone manner. By contrast, Polλ selectively introduced the correct dCTP opposite the modified dG in the case of cis-BP-dG adduct only, and did not bypass the stereoisomeric trans-adduct under any of the conditions examined. The results suggest that Polλ is a specialized polymerase that can process these kinds of lesions.