Nonsense
mutations in the essential gene SUP35 Saccharomyces cerevisiae.
Svetlana Chabelskaia (1), Michel Philippe (2), Galina Zhouravleva (1)
(1) Department of Genetics and Selection, St. Petersburg State University,
Universitetskaja nab., 7/9 199034, St. Petersburg, Russia
(sveta@btc.bio.pu.ru); (2) UMR6061 CNRS Génétique et Développement, Université
de Rennes I, 2 av. Pr. Léon Bernard, 35043 Rennes cedex, France
Termination of protein synthesis in eukaryotes is achieved by two interacting polypeptide chain release factors eRF1 and eRF3. Among them eRF1 recognizes nonsense codons while eRF3 stimulates polypeptide release from the ribosome in GTP and eRF1-depending manner. In S. cerevisiae eRF1 and eRF3 are encoded by essential genes called SUP45 and SUP35, respectively. Both proteins are needed for accurate translation termination in yeast. We have studied two mutations leading to the appearance of the premature nonsense codons (UAA) in the gene SUP35. These mutations are located in different regions of SUP35 gene and lead to the omnipotent nonsense suppressor phenotype. In vivo quantification of the nonsense suppressor efficiency was performed in these mutants. Western blot analysis has shown that full-length eRF3 protein is present in these mutants, but in the reduced level. Our data show that even very decreased level of eRF3 (up to 5% compared to wild type) is enough to provide cell viability. In shuffling experiments performed in different genetic backgrounds these mutations showed decreased ability to compensate SUP35 deletion in comparison with wild type. In addition these mutations lead to decreased spore viability. This work was supported in part by Award No.ST-012-0 of the U.S. Civilian Research & Development Foundation for the Independent States of the Former Soviet Union (CRDF) and personal grant to C. S. from the European Science Foundation (ESF) No. 2002/EG/02.