Itt1p, a novel protein inhibiting translation termination in Saccharomyces cerevisiae

BACKGROUND: Termination of translation in eukaryotes is controlled by two interacting polypeptide chain release factors, eRFl and eRF3. eRFl recognizes nonsense codons UAA, UAG and UGA, while eRF3 stimulates polypeptide release from the ribosome in a GTP- and eRFl – dependent manner. Recent studies has shown that proteins interacting with these release factors can modulate the efficiency of nonsense codon readthrough. RESULTS: We have isolated a nonessential yeast gene, which causes suppression of nonsense mutations, being in a multicopy state. This gene encodes a protein designated Itt1p, possessing a zinc finger domain characteristic of the TRIAD proteins of higher eukaryotes. Overexpression of Itt1p decreases the efficiency of translation termination, resulting in the readthrough of all three types of nonsense codons. Itt1p interacts in vitro with both eRFl and eRF3. Overexpression of eRFl, but not of eRF3, abolishes the nonsense suppressor effect of overexpressed Itt1p. CONCLUSIONS: The data obtained demonstrate that Itt1p can modulate the efficiency of translation termination in yeast. This protein possesses a zinc finger domain characteristic of the TRIAD proteins of higher eukaryotes, and this is a first observation of such protein being involved in translation

Elongation factor eEF1B modulates functions of the release factors eRF1 and eRF3 and the efficiency of translation termination in yeast

<p>Abstract</p> <p>Background</p> <p>Termination of translation in eukaryotes is controlled by two interacting polypeptide chain release factors, eRF1 and eRF3. While eRF1 recognizes nonsense codons, eRF3 facilitates polypeptide chain release from the ribosome in a GTP-dependent manner. Besides termination, both release factors have essential, but poorly characterized functions outside of translation.</p> <p>Results</p> <p>To characterize further the functions of yeast eRF1 and eRF3, a genetic screen for their novel partner proteins was performed. As a result, the genes for γ (<it>TEF4 </it>and <it>TEF3/CAM1</it>) and α (<it>TEF5</it>/<it>EFB1</it>) subunits of the translation elongation factor eEF1B, known to catalyze the exchange of bound GDP for GTP on eEF1A, were revealed. These genes act as dosage suppressors of a synthetic growth defect caused by some mutations in the <it>SUP45 </it>and <it>SUP35 </it>genes encoding eRF1 and eRF3, respectively. Extra copies of <it>TEF5 </it>and <it>TEF3 </it>can also suppress the temperature sensitivity of some <it>sup45 </it>and <it>sup35 </it>mutants and reduce nonsense codon readthrough caused by these omnipotent suppressors. Besides, overproduction of eEF1Bα reduces nonsense codon readthrough in the strain carrying suppressor tRNA. Such effects were not shown for extra copies of <it>TEF2</it>, which encodes eEF1A, thus indicating that they were not due to eEF1A activation.</p> <p>Conclusion</p> <p>The data obtained demonstrate involvement of the translation elongation factor eEF1B in modulating the functions of translation termination factors and suggest its possible role in GDP for GTP exchange on eRF3.</p