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tRNA Synthesis

Gail P. Mazzara, William H. McClain


The involvement of precursor RNAs in the biosynthesis of tRNA was first observed in mammalian cells. Results of these early studies were subsequently confirmed and extended with prokaryotic cells. For example, with bacteriophage T4 the terminal steps leading to the production of T4 tRNAPro and tRNASer have been defined in detail (McClain 1977). More recently, analysis of tRNA biosynthesis with eukaryotic cells has made substantial progress as a result of the technological developments in cloning and DNA sequencing. The study of tRNA biosynthesis in yeast has revealed the presence within certain tRNA genes of intervening sequences that are transcribed and subsequently excised from the precursor RNAs in a processing reaction that apparently has no counterpart in prokaryotic tRNA synthesis. In this paper we shall describe how it has been possible to elucidate the details of precursor RNA processing reactions to reveal the various steps in the pathway of tRNA biosynthesis.

The initial product of transcription of a tRNA gene is a longer RNA molecule (precursor RNA) that must be processed to yield mature tRNA. Because the precursor RNA contains extra nucleotide residues not present in the mature molecule, such processing includes one or more enzymatic cleavages of the precursor RNA to excise the functional tRNA. Additional processing events include enzymatic modification of nucleotide residues and addition of nucleotides to the terminal regions of precursor RNA molecules.

The discovery that tRNAs are synthesized via larger precursor RNAs has raised several questions related to the process by which these molecules are converted...

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