Ribonuclease P (<db_xref db="EC" dbkey="3.1.26.5"/>) (RNase P) [<cite idref="PUB00002604"/>, <cite idref="PUB00002589"/>, <cite idref="PUB00004402"/>] is a site specific endonuclease that generates mature tRNAs by catalysing the removal of the 5'-leader sequence from pre-tRNA to produce the mature 5'-terminus. It can also cleave other RNA substrates such as 4.5S RNA. In bacteria RNase P is known to be composed of two components: a large RNA (about 400 base pairs) encoded by rnpB, and a small protein (119 to 133 amino acids) encoded by rnpA. The RNA moiety of RNase P carries the catalytic activity; the protein component plays an auxiliary, but essential, role in vivo by binding to the 5'-leader sequence and broadening the substrate specificity of the ribozyme.The sequence of rnpA is not highly conserved, however there is, in the centralpart of the protein, a conserved basic region.