Abstract
RNase P is the endonuclease that removes 5' extensions from tRNA precursors. In its best-known form, the enzyme is composed of a catalytic RNA and a protein moiety variable in number and mass. This ribonucleoprotein enzyme is widely considered ubiquitous and apparently reached its highest complexity in the eukaryal nucleus, where it is typically composed of at least ten subunits. Here, we show that in the protist Trypanosoma brucei, two proteins are the sole forms of RNase P. They localize to the nucleus and the mitochondrion, respectively, and have RNase P activity each on their own. The protein-RNase P is, moreover, capable of replacing nuclear RNase P in yeast cells. This shows that complex ribonucleoprotein structures and RNA catalysis are not necessarily required to support tRNA 5' end formation in eukaryal cells.