Part of ribonuclease P (RNase P), a protein complex that generates mature tRNA molecules by cleaving their 5'-ends. Binds RNase P RNA. Endonucleolytic cleavage of RNA, removing 5'-extranucleotides from tRNA precursor. Optimum temperature is 70 degrees Celsius. Consists of a catalytic RNA component and at least 5 protein subunits. Forms a heterodimeric subcomplex with Rnp4. Reconstituted enzyme missing individual protein subunits is suboptimally active, showing each subunit contributes to optimization of activity. Belongs to the eukaryotic/archaeal RNase P protein component 1 family.