Arrangement and Transcription of Drosophila tRNA Genes

Abstract

Our knowledge of the details of tRNA biosynthesis in eukaryotic organisms is much more limited than that of prokaryotes (see Mazzara and McClain, this volume). The main stumbling block in unraveling the sequence of the complex enzymatic steps that lead from tRNA genes to mature tRNA has been the lack of well-characterized tRNA genes and of defined tRNA precursors. Many of the questions asked in an earlier review (Schaefer and Söll 1974) are still open. What is the arrangement of tRNA genes in the chromosomes? How is a tRNA gene organized; what is the nature of promoter, terminator, and operatorlike sites? What factors control the rate and extent of tRNA biosynthesis?

Progress in recent years was stimulated by the development of techniques for molecular cloning of DNA (Sinsheimer 1977), which allowed the isolation and study of single eukaryotic tRNA genes. We now have some insight into the organization of tRNA genes in the genome of yeast (Beckmann et al. 1977; Olson et al. 1979), Drosophila (Yen et al. 1977; Schmidt et al. 1978; Dunn et al. 1979), the nematode Caenorhabditis elegans (Cortese et al. 1978), and Xenopus laevis (Kressmann et al. 1978). In addition, the DNA sequences of a number of yeast tRNA genes have been elucidated (Goodman et al. 1977; Valenzuela et al. 1978; Ogden et al. 1979). These tRNA genes were shown to be noncolinear with their products; they contained intervening nucleotide sequences that are removed at the RNA level by novel enzymes of RNA metabolism (Knapp et...