When all's zed and done: the structure and function of RNase Z in prokaryotes

RNase Z is a widely distributed and often essential endoribonuclease that is responsible for the maturation of the 3'-end of a large family of transfer RNAs (tRNAs). Although it has been the subject of study for more than 25 years, interest in this enzyme intensified dramatically with the identification of the encoding gene in 2002. This led to the discovery of RNase Z in bacteria, in which the final step in the generation of the mature 3'-end of tRNAs had previously been assumed to be catalysed by exoribonucleases. It also led inevitably to structural studies, and the recent resolution of the structure of RNase Z in complex with tRNA has provided a detailed understanding of the molecular mechanisms of RNase Z substrate recognition and cleavage. The identification of the RNase Z gene also allowed the search for alternative substrates for this enzyme to begin in earnest. In this Review, we outline the important recent developments that have contributed to our understanding of this enzyme, particularly in prokaryotes.