Part of ribonuclease P, a protein complex that generates mature tRNA molecules by cleaving their 5'-ends. Endonucleolytic cleavage of RNA, removing 5'-extranucleotides from tRNA precursor. Consists of a catalytic RNA component and at least 4-5 protein subunits. Constitutively expressed (at protein level). Belongs to the eukaryotic/archaeal RNase P protein component 1 family.