Deployment of DNA polymerases beta and lambda in single-nucleotide and multinucleotide pathways of mammalian base excision DNA repair.

ABSTRACT: There exist two major base excision DNA repair (BER) pathways, namely single-nucleotide or "short-patch" (SP-BER), and "long-patch" BER (LP-BER). Both pathways appear to be involved in the repair of small base lesions such as uracil, abasic sites and oxidized bases. In addition to DNA polymerase ? (Pol?) as the main BER enzyme for repair synthesis, there is evidence for a minor role for DNA polymerase lambda (Pol?) in BER. In this study we explore the potential contribution of Pol? to both SP- and LP-BER in cell-free extracts. We measured BER activity in extracts of mouse embryonic fibroblasts using substrates with either a single uracil or the chemically stable abasic site analog tetrahydrofuran residue. The addition of purified Pol? complemented the pronounced BER deficiency of POLB-null cell extracts as efficiently as did Pol? itself. We have developed a new approach for determining the relative contributions of SP- and LP-BER pathways, exploiting mass-labeled nucleotides to distinguish single- and multinucleotide repair patches. Using this method, we found that uracil repair in wild-type and in Pol?-deficient cell extracts supplemented with Pol? was ?80% SP-BER. The results show that recombinant Pol? can contribute to both SP- and LP-BER. However, endogenous Pol?, which is present at a level ˜50% that of Pol? in mouse embryonic fibroblasts, appears to make little contribution to BER in extracts. Thus Pol? in cells appears to be under some constraint, perhaps sequestered in a complex with other proteins, or post-translationally modified in a way that limits its ability to participate effectively in BER.

SUBMITTER: Thapar U 

PROVIDER: S-EPMC6464370 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature