Structure and Catalytic Function of the Bacterial Ribonuclease P Ribozyme

Abstract

Ribonuclease P (RNase P) was present in the common ancestor of all life and was composed, at least in part, of RNA. This perspective is based on the observation that RNase P activity is present in organisms belonging to all three modern phylogenetic domains, and all of the cellular enzymes responsible for that activity have essential RNA subunits (see, e.g., Guerrier-Takada et al. 1983; Cherayil et al. 1987; LaGrandeur et al. 1993). Comparison of RNase P RNA sequences from representatives of all three phylogenetic domains reveals clear sequence and structural similarities (see, e.g., Forster and Altman 1990b; Tranguch and Engelke 1993; Haas et al. 1996a; Chen and Pace 1997). Thus, bacterial, archaeal and eukaryal RNase P RNAs are “homologous,” that is, they share ancestry. Such ancient heritage indicates a central role for RNA in the function of this enzyme.

RNase P catalyzes the hydrolysis of a specific phosphodiester bond in pre-tRNA to generate the 5′ end of mature tRNA. Understanding the role that the RNA plays in the function of RNase P requires knowledge of the enzyme’s structure and catalytic properties. In bacteria, the RNase P holoenzyme is a heterodimer composed of a single protein (~120 amino acids) and RNA (~400 nucleotides) components. In vivo, both subunits are essential for pre-tRNA processing and cell viability (Schedl and Primakoff 1973). However, under in vitro reaction conditions of high ionic strength, bacterial RNase P RNAs retain the substrate-binding and catalytic properties of the holoenzyme, and so are one class of ribozymes (Guerrier-Takada...