Mitochondrial tRNA methyltransferase that mediates methylation of cytosine to 5-methylcytosine (m5C) at position 34 of mt-tRNA(Met) (PubMed:27497299, PubMed:27214402, PubMed:27356879). mt-tRNA(Met) methylation at cytosine(34) takes place at the wobble position of the anticodon and initiates the formation of 5-formylcytosine (f(5)c) at this position (PubMed:27497299, PubMed:27214402, PubMed:27356879). mt-tRNA(Met) containing the f(5)c modification at the wobble position enables recognition of the AUA codon in addition to the AUG codon, expanding codon recognition in mitochondrial translation (PubMed:27497299, PubMed:27356879). cytidine(34) in mitochondrial tRNA + S-adenosyl-L-methionine = 5-methylcytidine(34) in mitochondrial tRNA + H(+) + S-adenosyl-L-homocysteine The disease is caused by variants affecting the gene represented in this entry. Belongs to the class I-like SAM-binding methyltransferase superfamily. RsmB/NOP family. Chimera. Truncated N-terminus.