The making of tRNAs and more - RNase P and tRNase Z.

Transfer-RNA (tRNA) molecules are essential players in protein biosynthesis. They are transcribed as precursors, which have to be extensively processed at both ends to become functional adaptors in protein synthesis. Two endonucleases that directly interact with the tRNA moiety, RNase P and tRNase Z, remove extraneous nucleotides on the molecule's 5'- and 3'-side, respectively. The ribonucleoprotein enzyme RNase P was identified almost 40 years ago and is considered a vestige from the "RNA world". Here, we present the state of affairs on prokaryotic RNase P, with a focus on recent findings on its role in RNA metabolism. tRNase Z was only identified 6 years ago, and we do not yet have a comprehensive understanding of its function. The current knowledge on prokaryotic tRNase Z in tRNA 3'-processing is reviewed here. A second, tRNase Z-independent pathway of tRNA 3'-end maturation involving 3'-exonucleases will also be discussed.