An alpha subtype methylase that recognizes the double-stranded sequence 5'-CYCGRG-3', methylates C-1 on both strands, and protects the DNA from cleavage by the BsoBI endonuclease. 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.