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. Author manuscript; available in PMC: 2011 Jul 15.
Published in final edited form as: Annu Rev Genet. 2009;43:143–166. doi: 10.1146/annurev-genet-102108-134205

Figure 2.

Figure 2

Diagram showing various possible levels and mechanisms of active DNA demethylation. (a) Base excision repair (BER) initiated by 5-methylcytosine (5-meC) DNA glycosylase. This is the predominant mechanism in plants but may also function in mammals. (b) Base excision repair initiated by coupled activities of 5-meC deaminase that converts 5-meC to T, and G/T mismatch DNA glycosylase that corrects the G/T mismatch. This appears to be the predominant mechanism in mammals but may also play a role in plants. (c) Nucleotide excision repair that removes methylated CpG dinucleotides. (d ) Oxidative removal of the methyl group. (e) Hydrolytic removal of the methyl group, releasing it as methanol.