DNA methyltransferases (Mtases) catalyze the transfer of theS-methyl group ofS-adenosylmethionine (SAM) to deoxycytosine (dC) or deoxyadenine (dA) bases within defined DNA sequences (1 ). Individual enzymes are specific for one or the other base, and modify at the 6-NH2 of dA (EC 2.1.1.72) or at the N4 or 5-C position of dC (EC 2.1.1.73) depending on the particular enzyme (2 ). The reaction is predominantly irreversible. Enzymes, such asO6 -methylguanine DNA Mtase, that participate in DNA repair processes will not be discussed here.
