Fig. 2
From: DNA methylation, the early-life social environment and behavioral disorders
Mechanisms of active DNA demethylation. Several demethylation reactions were suggested. Direct demethylation by a demethylase enzyme (dMTase; MBD2 is a putative candidate) could release a methyl moiety (CH 3 ) in the form of either methanol or formaldehyde. Alternatively, the methyl cytosine ring could be modified by either deamination catalyzed for example by AID or by the DNA methyltransferases (DNMT) which were shown to catalyze deamination of 5-methylcytidine in the absence of SAM or hydroxylation of the methyl moiety catalyzed by TET1. The modified base is then excised and repaired. Alternatively, the bond between the sugar and the base is cleaved (by glycosylases such as MBD4 or 5-methylcytosine glycosylase 5-MCDG) followed by repair. Repair proteins shown to be associated with demethylation were GADD45(a and b)