Part of ribonuclease P, a protein complex that generates mature tRNA molecules by cleaving their 5'-ends. The RNA is catalytic, but its KM for pre-tRNA is 170-fold decreased in the presence of the 4 known protein subunits (Rnp1-4). The protein subunits also decrease the amount of Mg(2+) needed for activity. Endonucleolytic cleavage of RNA, removing 5'-extranucleotides from tRNA precursor. kcat is 9.5 min(-1). For enzyme reconstituted with RNA and 4 known subunits (Rnp1-4). Consists of a catalytic RNA component and at least 4 protein subunits. Forms a subcomplex with Rnp4 which stimulates the catalytic RNA. Interaction with Rnp4 is mediated by the N-terminus; short deletion mutants are still able to reconstitute RNase P activity. Belongs to the eukaryotic/archaeal RNase P protein component 1 family.