Base Excision Repair

Base excision repair (BER) recognizes, excises, and replaces DNA bases damaged by endogenous oxidation, methylation, deamination, and hydrolytic processes (11,12). One of several related glycosylases, each specialized for a particular type of base modification, releases the damaged base from the sugar-phosphate backbone of the DNA molecule. This is followed by cleavage at the abasic site by APE1 endonuclease, with a minor contribution from APE2 en-donuclease. DNApolp fills in the one-nucleotide gap, followed by a sealing of the nick by XRCC1-ligase 3, although there are at least four adenosine triphosphate (ATP)-dependent DNA ligases.

In addition, single-strand DNA breaks also may be dealt with by enzymes from the BER pathway. Poly(ADP-ribose) polymerase enzymes, XRCC1, and polynucleotide kinase participate in binding the single-strand breaks and initiation of repair of a single-strand break.

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