The effect of methylation and hydroxymethylation of cytosine on activity and fidelity of Pol λ and Pol β

Abstract

Сytosine methylation in CpG dinucleotides is the most common epigenetic mark in human cells. Under active demethylation process 5-methylcytosine (mC) can be converted to 5-hydroxymethylcytosine (hmC). Cytosine methylation increases the risk of adjacent nucleotide damage, including the oxidation of guanine. DNA polymerases might encounter mC and hmC during DNA repair or translesion synthesis. Here, we analyze the activity of X-family polymerases Pol β and Pol λ opposite mC and hmC as well as opposite 8-oxoG adjacent to mC in the TCG context. We demonstrate that hmC has no pronounced effect on Pol β and Pol λ activity while cytosine methylation moderately suppresses the efficiency of dGMP incorporation by Pol β but not Pol λ. Pol λ was not affected by + 2 cytosine methylation when synthesizing across 8-oxoG. In contrast, cytosine methylation slightly increased incorporation of dCMP opposite 8-oxoG adjacent to mC but reduced the extension of the 8-oxoG:C pair by Pol β.