an N(3)-methylcytidine in mRNA + S-adenosyl-L-homocysteine + H(+) => a cytidine in mRNA + S-adenosyl-L-methionine
an n(3)-methylcytidine in mrna + s-adenosyl-l-homocysteine + h(+) => a cytidine in mrna + s-adenosyl-l-methionine