Viable nonsense mutants for the essential gene SUP45 of Saccharomyces cerevisiae
1 Université de Rennes 1, CNRS UMR 6061, IFR 97, 2 av. Pr. Léon Bernard 35043 Rennes Cedex, France
2 Department of Genetics, St Petersburg State University, Universitetskaya emb. 7/1, 199034, St Petersburg, Russia
BMC Molecular Biology 2003, 4:2 doi:10.1186/1471-2199-4-2Published: 10 February 2003
Termination of protein synthesis in eukaryotes involves at least two polypeptide release factors (eRFs) – eRF1 and eRF3. The highly conserved translation termination factor eRF1 in Saccharomyces cerevisiae is encoded by the essential gene SUP45.
We have isolated five sup45-n (n from nonsense) mutations that cause nonsense substitutions in the following amino acid positions of eRF1: Y53 → UAA, E266 → UAA, L283 → UAA, L317 → UGA, E385 → UAA. We found that full-length eRF1 protein is present in all mutants, although in decreased amounts. All mutations are situated in a weak termination context. All these sup45-n mutations are viable in different genetic backgrounds, however their viability increases after growth in the absence of wild-type allele. Any of sup45-n mutations result in temperature sensitivity (37°C). Most of the sup45-n mutations lead to decreased spore viability and spores bearing sup45-n mutations are characterized by limited budding after germination leading to formation of microcolonies of 4–20 cells.
Nonsense mutations in the essential gene SUP45 can be isolated in the absence of tRNA nonsense suppressors.