tRNA Precursors in RNase P Mutants

Abstract

It is generally accepted that the transcription products of tRNA genes are unmodified and larger than mature size, and that these precursors are subsequently modified and processed to form mature tRNA molecules (Schäfer and Söll 1974; Altman 1975; Smith 1976; Perry 1976; Shimura and Sakano 1977). Although the tRNA precursors were first discovered in mammalian cells, most of our knowledge about the processing of tRNA precursors has come from Escherichia coli, where genetic analysis and nucleotide sequencing are easily applicable.

Ever since Altman and Smith (1971; Altman 1971) found a precursor molecule of su⁺3 tRNA₁^Tyr carrying extra nucleotides at both the 5′ and 3′ terminals of the tRNA molecule, much effort has been directed toward the characterization and processing of precursor molecules of tRNAs encoded by E. coli and phage T4. The sequences of several other precursors for E. coli and T4-encoded tRNAs have also been shown to contain extra nucleotides at both their 5′ and 3′ terminals (Barrell et al. 1974; Chang and Carbon 1975; Guthrie 1975). In addition, the presence of multimeric precursors that contain two or more tRNA sequences within a single molecule has been indicated (Guthrie et al. 1973; Schedl et al. 1974, 1976; Sakano and Shimura 1975, 1978; Ilgen et al. 1976). As to the specific nucleases involved in the cleavage of the tRNA gene transcripts, RNase P was the first enzyme shown to participate in the processing of E. coli tRNA precursors. This enzyme has been purified from the ribosome wash fraction of E....