Transfer RNA maturation in Chlamydomonas mitochondria, chloroplast and the nucleus by a single RNase P protein

The maturation of tRNA precursors involves the 5 cleavage of leader sequences by an essential endonuclease called RNase P. Beyond the ancestral ribonucleoprotein (RNP) RNase P, a second type of RNase P called PRORP (protein-only RNase P) evolved in eukaryotes. The current view on the distribution of RNase P in cells is that multiple RNPs, multiple PRORPs or a combination of both, perform specialised RNase P activities in the different compartments where gene expression occurs. Here, we identify a single gene encoding PRORP in the green alga Chlamydomonas reinhardtii while no RNP is found. We show that its product, CrPRORP, is triple-localised to mitochondria, the chloroplast and the nucleus. Its downregulation results in impaired tRNA biogenesis in both organelles and the nucleus. CrPRORP, as a single-subunit RNase P for an entire organism, makes up the most compact and versatile RNase P machinery described in either prokaryotes or eukaryotes. Significance Statement RNase P removes 5 leader sequences of tRNA precursors. Here we demonstrate that Chlamydomonas has a single RNase P gene whose gene product acts in the chloroplast, mitochondria and the nucleus, thus contradicting the dogma that different RNase P systems act in each of these cellular compartments.