A beta subtype methylase (PubMed:10648519). Recognizes the double-stranded sequence 5'-CCN(7)GG-3', methylates C-2 on both strands, and protects the DNA from cleavage by the BslI endonuclease (PubMed:12654995). a 2'-deoxycytidine in DNA + S-adenosyl-L-methionine = an N(4)-methyl-2'-deoxycytidine in DNA + H(+) + S-adenosyl-L-homocysteine Belongs to the N(4)/N(6)-methyltransferase family. N(4) subfamily.