This is probably the methylase that recognizes and modifies 5'-CpG-3'. a 2'-deoxycytidine in DNA + S-adenosyl-L-methionine = a 5-methyl-2'-deoxycytidine in DNA + H(+) + S-adenosyl-L-homocysteine Probably requires another subunit for function. Transcribed in the delayed early phase of replication. About 20% of the cytosine bases in the genome are methylated on 5'-CpG-3' sequences. Belongs to the class I-like SAM-binding methyltransferase superfamily. C5-methyltransferase family.