Figure 1
From: 5-hydroxymethylcytosine and its potential roles in development and cancer
Chemical structures of 5-methylcytosine (5mC) and its oxidation products 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC). The potential involvement of these modified cytosine bases in several pathways of passive (replication-dependent) and active (replication-independent) DNA demethylation is indicated. One active demethylation pathway is proposed to include consecutive oxidation steps followed by removal of 5caC by thymine DNA glycosylase (TDG) in a base excision repair (BER) scheme or by decarboxylation arriving back at cytosine (C). DNMT, DNA methyltransferase.