Mitochondrial ribonuclease P is a eukaryotic-specific, protein-only enzyme that catalyzes 5' end maturation of mitochondrial precursor transfer RNAs. It comprises 3 subunits (none of which are homologous to the RNA-based RNase P proteins): a tRNA methyltransferase, a short-chain dehydrogenase/reductase, and a metallonuclease, which houses the RNase P active site. (Adapted from
PMID:27187488.)