Nonsense Suppressor tRNA in Schizosaccharomyces pombe

Abstract

The study of informational suppression in prokaryotes played an important role in the elucidation of the genetic code and of the detailed mechanism of protein biosynthesis (for a review, see Steege and Söll 1978). Some areas in the molecular biology of bacteria have benefited greatly from studies of suppression: the unraveling of the steps of tRNA biosynthesis, the formation and function of modified nucleotides in tRNA, and structure-function relations in tRNA (for reviews, see Smith 1976; McClain 1977; Steege and Söll 1978). Our understanding of the modes of tRNA recognition by aminoacyl-tRNA synthetases (Söll and Schimmel 1974; Ozeki et al., this volume) or by tRNA-modifying enzymes (McClain 1977) has been refined by the genetic opportunities provided by nonsense suppression. Our knowledge of informational suppression in eukaryotes is most advanced in yeasts. An excellent summary of the earlier genetic data has been provided by Hawthorne and Leupold (1974). In the past few years, biochemical studies have begun to characterize the suppression mechanism, mostly in Saccharomyces cerevisiae. In this organism, nonsense suppressor tRNAs of the amber (UAG) and ocher (UAA) types have been characterized in vitro (Capecchi et al. 1975; Gesteland et al. 1976). Both tyrosine- and serine-inserting amber suppressor tRNAs have been sequenced (Piper, this volume), and the nucleotide sequence of the gene for an ocher suppressor tRNA^Tyr is known (Goodman et al. 1977). This report reviews the state of suppressor genetics in Schizosaccharomyces pombe and describes the identification and the nucleotide sequences of two opal suppressor tRNAs from this organism.