Effects of Tet-Induced OxidationProducts of 5-Methylcytosineon DNA Replication in Mammalian Cells.

Recently 5-hydroxymethyl-2′-deoxycytidine(5hmdC), 5-formyl-2′-deoxycytidine(5fdC), and 5-carboxyl-2′-deoxycytidine (5cadC) were discoveredin mammalian DNA as oxidation products of 5-methyl-2′-deoxycytidine(5mdC) induced by the ten-eleven translocation family of enzymes.These oxidized derivatives of 5mdC may not only act as intermediatesof active cytosine demethylation in mammals but also serve as epigeneticmarks on their own. It remains unclear how 5hmdC, 5fdC, and 5cadCaffect DNA replication in mammalian cells. Here, we examined the effectsof the three modified nucleosides on the efficiency and accuracy ofDNA replication in HEK293T human kidney epithelial cells. Our resultsdemonstrated that a single, site-specifically incorporated 5fdC or5cadC conferred modest drops, by approximately 30%, in replicationbypass efficiency without inducing detectable mutations in human cells,whereas replicative bypass of 5hmdC is both accurate and efficient.The lack of pronounced perturbation of these oxidized 5mdC derivativeson DNA replication is consistent with their roles in epigenetic regulationof gene expression. [ABSTRACT FROM AUTHOR]