Catalytic ribonuclease 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, PubMed:25953853, PubMed:34715011). The presence of TRMT10C/MRPP1, HSD17B10/MRPP2 is required to catalyze tRNA molecules in their 5'-ends (PubMed:25953853). {ECO:0000269|PubMed:18984158, ECO:0000269|PubMed:25953853, ECO:0000269|PubMed:34715011}. This is the function of PRORP (protein only RNase P catalytic subunit, Ensembl gene identifier ENSG00000100890).