PRORPs (protein-only RNase P) are a class of RNA processing enzymes that catalyze maturation of the 5' end of precursor tRNAs in Eukaryotes [1]. Arabidopsis thaliana contains PRORP enzymes (PRORP1, PRORP2 and PRORP3) where PRORP1 localizes to mitochondria as well as chloroplasts, while PRORP2 and PRORP3 are found in the nucleus. In humans and most other metazoans, mt-RNase P is composed of three protein subunits (mitochondrial RNase P proteins 1-3; MRPP1-3), homologs to the Arabidopsis thaliana PRORP1-3. This domain corresponds to the metallonuclease domain of PRORPs. PRORP1 has 22% sequence identity to the human homologue MRPP3. PRORP1 crystal structure shows a V-shaped tripartite structure with a C-terminal metallonuclease domain of the NYN (N4BL1, YacP-like nuclease) family, with a typical and functional two-metal-ion catalytic site that has conserved aspartate residues [2].

1: Nuclear Protein-Only Ribonuclease P2 Structure and Biochemical Characterization Provide Insight into the Conserved Properties of tRNA 5' End Processing Enzymes. Karasik A, Shanmuganathan A, Howard MJ, Fierke CA, Koutmos M; J Mol Biol. 2016;428:26-40. PMID:26655022

2: Structure of the nuclease subunit of human mitochondrial RNase P. Reinhard L, Sridhara S, Hallberg BM; Nucleic Acids Res. 2015;43:5664-5672. PMID:25953853