A single Arabidopsis organellar protein has RNase P activity.

The ubiquitous endonuclease RNase P is responsible for the 5' maturation of tRNA precursors. Until the discovery of human mitochondrial RNase P, these enzymes had typically been found to be ribonucleoproteins, the catalytic activity of which is associated with the RNA component. Here we show that, in Arabidopsis thaliana mitochondria and plastids, a single protein called 'proteinaceous RNase P' (PRORP1) can perform the endonucleolytic maturation of tRNA precursors that defines RNase P activity. In addition, PRORP1 is able to cleave tRNA-like structures involved in the maturation of plant mitochondrial mRNAs. Finally, we show that Arabidopsis PRORP1 can replace the bacterial ribonucleoprotein RNase P in Escherichia coli cells. PRORP2 and PRORP3, two paralogs of PRORP1, are both localized in the nucleus.