DNA polymerase action on an oligonucleotide containing a site-specifically located N-(deoxyguanosin-8-yl)-1-aminopyrene

A 25mer oligonucleotide containing a single N-(deoxyguanosin-8-yl)-1-aminopyrene (dG AP ), the major DNA adduct formed by reductively activated 1-nitropyrene, was synthesized. The adduct was located at nucleotide 21 from the 3' end. DNA synthesis on this template by human DNA polymerases α and β, HIV reverse transcriptase, Sequenase (version 2.0) and Klenow fragment of DNA polymerase I was strongly blocked at the nucleotide 3' to the adduct site. Only when a 3'→5' exonuclease-deficient Klenow fragment was used was incorporation of a nucleotide opposite the adduct observed. Nevertheless, extension beyond the adduct site did not occur to a significant extent. Only a relatively small proportion of full-length product (<5%) WAS DETECTED. IN THE PRESENCE OF MN 2+ , the efficiency of bypass with this polymerase increased. When a 20mer primer was elongated in the presence of only one nucleotide triphosphate, deoxycytidylic acid was preferentially incorporated opposite the adduct. Deoxycytidine opposite the adduct was also preferred when a set of 21mer primers (containing each of the four nucleotides opposite dG AP ) were elongated to a full-length product in the presence of all four deoxynucleotide triphosphates. In order to confirm these results, extension of a 15mer primer was carried out with all four deoxynucleotide triphosphates and the products were isolated. Maxam-Gilbert sequencing of each elongation product showed that primer extension occurred in an error-free manner. We conclude that dG AP is a strong block of DNA replication. However, when translesion synthesis occurs, it is largely accurate