N4-methylcytidine (m4C) methyltransferase responsible for the methylation of position C839 in mitochondrial 12S rRNA (PubMed:31665743, PubMed:32371392). Involved in the stabilization of 12S rRNA folding, therefore facilitating the assembly of the mitochondrial small ribosomal subunits (PubMed:31665743, PubMed:32371392). cytidine(839) in 12S rRNA + S-adenosyl-L-methionine = H(+) + N(4)-methylcytidine(839) in 12S rRNA + S-adenosyl-L-homocysteine Belongs to the methyltransferase superfamily. RsmH family. Truncated N-terminus.