Fig. 2.
The transmethylation reaction catalyzed DNA methyltransferases (DNMTs). DNMTs catalyze the transfer of the methyl donor group from S-adenosylmethionine (dashed box) to the 5 position of the pyrimidine ring of cytosines within CpG di-nucleotides in genomic DNA. The reaction results in the production of 5-Me-Cytosine and S-adenosylhomocysteine.