Fig. 2.

Methylation and demethylation of DNA. DNA methyltransferases (DNMTs) methylate cytosine (C) at site C5, creating 5-methylcytosine (m5C). Through the proposed demethylation route, ten-eleven translocation enzymes catalyze the repeated oxidation of m5C to 5-(hydroxymethyl)cytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxycytosine (5caC). In order to create apyrimidinic (AP) sites, 5fC and 5caC are removed by the G/T-mismatch-specific thymine DNA glycosylase, followed by base excision repair (BER) to reinstall the cytosine