Isolation of the SUP45 omnipotent suppressor gene of Saccharomyces cerevisiae and characterization of its gene product.
The Saccharomyces cerevisiae SUP45+ gene has been isolated from a genomic clone library by genetic complementation of paromomycin sensitivity, which is a property of a mutant strain carrying the sup45-2 allele. This plasmid complements all phenotypes associated with the sup45-2 mutation, including nonsense suppression, temperature sensitivity, osmotic sensitivity, and paromomycin sensitivity. Genetic mapping with a URA3+-marked derivative of the complementing plasmid that was integrated into the chromosome by homologous recombination demonstrated that the complementing fragment contained the SUP45+ gene and not an unlinked suppressor. The SUP45+ gene is present as a single copy in the haploid genome and is essential for viability. In vitro translation of the hybrid-selected SUP45+ transcript yielded a protein of Mr = 54,000, which is larger than any known ribosomal protein. RNA blot hybridization analysis showed that the steady-state level of the SUP45+ transcript is less than 10% of that for ribosomal protein L3 or rp59 transcripts. When yeast cells are subjected to a mild heat shock, the synthesis rate of the SUP45+ transcript was transiently reduced, approximately in parallel with ribosomal protein transcripts. Our data suggest that the SUP45+ gene does not encode a ribosomal protein. We speculate that it codes for a translation-related function whose precise nature is not yet known.
D000199:Actins / Q000235:genetics; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000235:genetics*; D005800:Genes, Fungal; D012269:Ribosomal Proteins / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D013489:Suppression, Genetic; D014170:Transformation, Genetic
D000199:Actins; D005656:Fungal Proteins; D012269:Ribosomal Proteins