Biochemical Characterization of RNase P: A tRNA Processing Activity with Protein and RNA Components

Abstract

RNase P is an Escherichia coli endonuclease that was originally identified by its ability to generate a 5′ mature product from the precursor to the psu⁺ 3 amber suppressor derived from tRNA₁^Tyr (Robertson et al. 1972). Based on this observation, selection techniques were devised that allowed the isolation of temperature-sensitive mutants defective in RNase P function (Schedl and Primakoff 1973; Ozeki et al. 1974). Genetic analyses have established that mutations conferring thermolabile RNase P activity can arise at two distinct loci, rnpA at 77 minutes and rnpB at 67 minutes (Kubokawa et al. 1976). A large number of tRNA precursors accumulate in these mutants at the nonpermissive temperature (Schedl et al. 1974; Ikemura et al. 1975; Ilgen et al. 1976; Sakano and Shimura 1978), suggesting that RNase P is required for the synthesis of all E. coli tRNAs. When bacteriophage T4 infections of RNase P mutants are performed at high temperature, none of the eight phage-specific tRNAs are synthesized; two dimeric precursors and one monomeric precursor accumulate (Abelson et al. 1974; Guthrie 1975). The RNA profiles of the two genetic classes appear to be identical (Shimura et al., this volume).

A number of mono- and dimeric precursors have been shown to be cleaved accurately by RNase P in vitro (Altman and Smith 1971; Barrell et al. 1974; Guthrie 1975; Chang and Carbon 1975). Comparison of nucleotides at and around these cleavage sites reveals that enzymatic recognition is not sequence-specific. A variety of data are consistent with the prediction that RNase...