Skip Navigation
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Your Environment. Your Health.

Publication Detail

Title: AP endonuclease 1 prevents the extension of a T/G mismatch by DNA polymerase β to prevent mutations in CpGs during base excision repair.

Authors: Lai, Yanhao; Jiang, Zhongliang; Zhou, Jing; Osemota, Emmanuel; Liu, Yuan

Published In DNA Repair (Amst), (2016 07)

Abstract: Dynamics of DNA methylation and demethylation at CpG clusters are involved in gene regulation. CpG clusters have been identified as hot spots of mutagenesis because of their susceptibility to oxidative DNA damage. Damaged Cs and Gs at CpGs can disrupt a normal DNA methylation pattern through modulation of DNA methylation and demethylation, leading to mutations and deregulation of gene expression. DNA base excision repair (BER) plays a dual role of repairing oxidative DNA damage and mediating an active DNA demethylation pathway on CpG clusters through removal of a T/G mismatch resulting from deamination of a 5mC adjacent to a guanine that can be simultaneously damaged by oxidative stress. However, it remains unknown how BER processes clustered lesions in CpGs and what are the consequences from the repair of these lesions. In this study, we examined BER of an abasic lesion next to a DNA demethylation intermediate, the T/G mismatch in a CpG dinucleotide, and its effect on the integrity of CpGs. Surprisingly, we found that the abasic lesion completely abolished the activity of thymine DNA glycosylase (TDG) for removing the mismatched T. However, we found that APE1 could still efficiently incise the abasic lesion leaving a 3-terminus mismatched T, which was subsequently extended by pol β. This in turn resulted in a C to T transition mutation. Interestingly, we also found that APE1 3'-5' exonuclease activity efficiently removed the mismatched T, thereby preventing pol β extension of the mismatched nucleotide and the resulting mutation. Our results demonstrate a crucial role of APE1 3'-5' exonuclease activity in combating mutations in CpG clusters caused by an intermediate of DNA demethylation during BER.

PubMed ID: 27183823 Exiting the NIEHS site

MeSH Terms: 5-Methylcytosine/metabolism; Base Pair Mismatch; CpG Islands; DNA Damage; DNA Methylation; DNA Polymerase beta/genetics*; DNA Polymerase beta/metabolism; DNA Repair*; DNA-(Apurinic or Apyrimidinic Site) Lyase/genetics*; DNA-(Apurinic or Apyrimidinic Site) Lyase/metabolism; DNA/genetics*; DNA/metabolism; Humans; Mutation; Thymine DNA Glycosylase/genetics*; Thymine DNA Glycosylase/metabolism

to Top