Involved in de novo DNA methylation. Involved in RNA-directed DNA methylation (RdDM). a 2'-deoxycytidine in DNA + S-adenosyl-L-methionine = a 5-methyl-2'-deoxycytidine in DNA + H(+) + S-adenosyl-L-homocysteine Belongs to the class I-like SAM-binding methyltransferase superfamily. DRM-methyltransferase family.