DNA ligase I fidelity mediates the mutagenic ligation of pol β oxidized nucleotide insertion products and base excision repair intermediates with mismatches

Abstract

DNA ligase I (LIG1) completes base excision repair (BER) pathway at the last nick sealing step following DNA polymerase (pol) {beta} gap filling DNA synthesis. We previously reported that pol {beta} 8-oxo-2-deoxyribonucleoside 5-triphosphate (8-oxodGTP) insertion confounds LIG1 leading to the formation of ligation failure products with 5-adenylate (AMP) block. Here, we report the mutagenic ligation of pol {beta} 8-oxodGTP insertion products and an inefficient substrate-product channeling from pol {beta} Watson-Crick like dG:T mismatch insertion to DNA ligation by LIG1 mutant with perturbed fidelity (E346A/E592A) in vitro. Moreover, our results revealed that the substrate discrimination of LIG1 for the nicked repair intermediates with preinserted 3-8-oxodG or mismatches is governed by the mutations at both E346 and E592 residues. Finally, we found that Aprataxin (APTX) and Flap Endonuclease 1 (FEN1), as compensatory DNA-end processing enzymes, can remove 5-AMP block from the abortive ligation products with 3-8-oxodG or all possible 12 non-canonical base pairs. These findings contribute to understand the role of LIG1 as an important determinant of faithful BER, and how a multi-protein complex (LIG1, pol {beta}, APTX and FEN1) can coordinate to hinder the formation of mutagenic repair intermediates with damaged or mismatched ends at the downstream steps of the BER pathway.