The genetic fine structure of nonsense suppressors in Schizosaccharomyces pombe

Abstract

Meiotic fine-structure maps of two efficient UGA suppressors of Schizosaccharomyces pombe which are known (sup8-e) or inferred (sup10-e) to code for two leucine tRNAs carrying the mutant anticodon U(*)CA (Kohli et al. 1979, 1980a, b; Wetzel et al. 1979; Mao et al. 1981) are presented. In both cases, the recombination frequencies given by the primary site of the anticodon mutation fitwell into the map defined by the sites of a number of inactivating secondary mutations. This contrasts the corresponding situation found in the serine tRNA genes sup3 and sup9 where the anticodon site exhibits a specific marker effect which strongly increases recombination frequencies in crosses with all revertant sites, due to a decrease in the efficiency of excision repair of base-pair mismatches whenever the anticodon site is included in hybrid-DNA (Hofer et al. 1979; Munz and Leupold 1979; Thuriaux et al. 1980). A pronounced specific marker effect which leads to a several fold increase of the recombination frequencies over those expected is observed, however, at one of the secondary inactivating sites mapping in the leucine tRNA gene sup8.

Nonsense suppression in Dictyostelium discoideum

“…Nonsense suppressors are defined as tRNAs that insert amino acids at positions in a message containing a translational stop codon. Nonsense suppressor tRNA genes have been extensively studied in bacteria [Celis and Smith, 1979;Steege and SOH, 19791 but also in the eukaryotes Saccharomyces cerevisiae [Sherman, 19821 and Schizzosaccharomyces pombe [Munz et al, 1983;Hottinger et al, 19821. Nonsense suppressors were isolated also from Caenorhabditis elegans [Wills et al, 1983;Hodgkin, 1985;Fire, 19861, and recently suppressor tRNA genes were expressed in Drosophila melanogaster [Doerig et al, 19881 and in human cell lines [Laski et al, 1982;Temple et al, 1982;Laski et al, 1984;Capone et al, 19851. Certainly for Escherichia coli and yeast the availability of a significant collection of defined suppressors was crucial for the rapid development of genetics in these systems, and nonsense suppression as a general conditional-lethal system will be of great value for higher eukaryotes as well.…”