Evolutionary perspective on the structure and function of ribonuclease P, a ribozyme

Ribonuclease P (RNase P) is a key enzyme in the biosynthesis of tRNA (for reviews, see references 3, 11, and 51).It is an RNA-processing endonuclease that specifically cleaves precursors of tRNA, releasing 5Ј precursor sequences and thereby forming the mature 5Ј ends of the tRNAs.RNase P is involved in processing all species of tRNA and is present in all cells and organelles that carry out tRNA synthesis.It is a particularly interesting enzyme because of its composition; it is a ribonucleoprotein (37).The nature of RNase P has been investigated for a broad diversity of organisms, including representatives of all the phylogenetic domains: Archaea, (eu)Bacteria, and Eucarya (see reference 72 for phylogenetic nomenclature).In the case of the enzyme from Bacteria, RNase P contains a catalytic RNA, or ribozyme (22,62).The secondary structure of the bacterial RNase P RNA has now been determined, models for its three-dimensional structure have been proposed, and numerous correlations between catalytic function and structure are being discovered.The purpose of this minireview is to provide an overview of RNase P, with emphasis on the structure of the bacterial RNase P RNA and how it varies between different organisms.Any understanding of the function of this unusual type of enzyme will rest on knowledge of its structure and patterns of variation.