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 = an n(3)-methylcytidine in mrna + s-adenosyl-l-homocysteine + h(+)