6ph6

Publication Abstract from PubMed

DNA polymerase beta has two DNA-binding domains that interact with the opposite sides of short DNA gaps. These domains contribute two activities that modify the 5'- and 3'-margins of gapped DNA during base excision repair. DNA gaps greater than one-nucleotide pose an architectural and logistical problem for the two domains to interact with their respective DNA termini. Here, crystallographic and kinetic analyses of two-nucleotide gap-filling DNA synthesis revealed that the fidelity of DNA synthesis depends on local sequence context. This was due to template dynamics that altered which of the two template nucleotides in the gap served as the coding nucleotide. We observed that when a purine nucleotide is in the first coding position, DNA synthesis fidelity is similar to that observed with a one-nucleotide gap. However, when the initial templating nucleotide is a pyrimidine, fidelity was decreased. If the first templating nucleotide was cytidine, there was a significantly higher probability that the downstream template nucleotide coded for the incoming nucleotide. This dNTP-stabilized misalignment reduced base-substitution and frameshift-deletion fidelities. A crystal structure of a binary DNA product complex revealed that the cytidine in the first templating site is in an extra-helical position, permitting the downstream template nucleotide to occupy the coding position. These results indicate that DNA polymerase beta can induce a strain in the DNA that modulates the position of the coding nucleotide and thereby impacts the identity of the incoming nucleotide. Our findings demonstrate that "correct" DNA synthesis can result in errors when template dynamics induce coding ambiguity.

DNA polymerase beta nucleotide-stabilized template misalignment fidelity depends on local sequence context.,Howard MJ, Cavanaugh NA, Batra VK, Shock DD, Beard WA, Wilson SH J Biol Chem. 2019 Dec 4. pii: RA119.010594. doi: 10.1074/jbc.RA119.010594. PMID:31801827^[5]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.