A methylase, recognizes the double-stranded sequence 5'-CYCGRG-3', methylates C-1 on both strands, and protects the DNA from cleavage by the AquI endonuclease. a 2'-deoxycytidine in DNA + S-adenosyl-L-methionine = a 5-methyl-2'-deoxycytidine in DNA + H(+) + S-adenosyl-L-homocysteine Heterodimer of an alpha and a beta subunit. Corresponds to the N-terminal half of the enzymatic domain. Belongs to the class I-like SAM-binding methyltransferase superfamily. C5-methyltransferase family.