Mitochondrial tRNA N(1)-methyltransferase involved in mitochondrial tRNA maturation (PubMed:18984158, PubMed:21593607, PubMed:23042678, PubMed:27132592). Component of mitochondrial ribonuclease P, a complex composed of TRMT10C/MRPP1, HSD17B10/MRPP2 and PRORP/MRPP3, which cleaves tRNA molecules in their 5'-ends (PubMed:18984158). Together with HSD17B10/MRPP2, forms a subcomplex of the mitochondrial ribonuclease P, named MRPP1-MRPP2 subcomplex, which displays functions that are independent of the ribonuclease P activity (PubMed:23042678, PubMed:29040705). The MRPP1-MRPP2 subcomplex catalyzes the formation of N(1)-methylguanine and N(1)-methyladenine at position 9 (m1G9 and m1A9, respectively) in tRNAs; TRMT10C/MRPP1 acting as the catalytic N(1)-methyltransferase subunit (PubMed:23042678). The MRPP1-MRPP2 subcomplex also acts as a tRNA maturation platform: following 5'-end cleavage by the mitochondrial ribonuclease P complex, the MRPP1-MRPP2 subcomplex enhances the efficiency of 3'-processing catalyzed by ELAC2, retains the tRNA product after ELAC2 processing and presents the nascent tRNA to the mitochondrial CCA tRNA nucleotidyltransferase TRNT1 enzyme (PubMed:29040705). In addition to tRNA N(1)-methyltransferase activity, TRMT10C/MRPP1 also acts as a mRNA N(1)-methyltransferase by mediating methylation of adenosine residues at the N(1) position of MT-ND5 mRNA (PubMed:29072297). Associates with mitochondrial DNA complexes at the nucleoids to initiate RNA processing and ribosome assembly. adenosine(9) in tRNA + S-adenosyl-L-methionine = H(+) + N(1)-methyladenosine(9) in tRNA + S-adenosyl-L-homocysteine guanosine(9) in tRNA + S-adenosyl-L-methionine = H(+) + N(1)-methylguanosine(9) in tRNA + S-adenosyl-L-homocysteine an adenosine in mRNA + S-adenosyl-L-methionine = an N(1)-methyladenosine in mRNA + H(+) + S-adenosyl-L-homocysteine Component of mitochondrial ribonuclease P, a complex composed of TRMT10C/MRPP1, HSD17B10/MRPP2 and PRORP/MRPP3.(PubMed:18984158). Interacts with HSD17B10/MRPP2; forming the MRPP1-MRPP2 subcomplex of the mitochondrial ribonuclease P complex (PubMed:23042678, PubMed:29040705). Interacts with GRSF1 (PubMed:23473034). The disease is caused by variants affecting the gene represented in this entry. Belongs to the class IV-like SAM-binding methyltransferase superfamily. TRM10 family. It is uncertain whether Met-1 or Met-7 is the initiator. The identity of the enzyme catalyzing mitochondrial mRNA N(1)-methyltransferase is unclear. According to a report, mitochondrial mRNA N(1)-methyltransferase activity is catalyzed by TRMT61B (AC Q9BVS5) (PubMed:29107537). According to a second report, it is mediated by TRMT10C (PubMed:29072297). As both reports only tested one protein (either TRMT61B or TRMT10C), it is possible that both proteins have this activity. Extended N-terminus. Truncated N-terminus.