Abstract
BackgroundTermination 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.ResultsTo 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 (TEF4 and TEF3/CAM1) and α (TEF5/EFB1) 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 SUP45 and SUP35 genes encoding eRF1 and eRF3, respectively. Extra copies of TEF5 and TEF3 can also suppress the temperature sensitivity of some sup45 and sup35 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 TEF2, which encodes eEF1A, thus indicating that they were not due to eEF1A activation.ConclusionThe 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.
Highlights
Termination of translation in eukaryotes is controlled by two interacting polypeptide chain release factors, eRF1 and eRF3
We found that extra copies of genes which encode the γ (TEF3/CAM1 and TEF4) and α (TEF5/EFB1) subunits of the translation elongation factor eEF1B, known to catalyze the exchange of bound GDP for GTP on eEF1A, suppressed synthetic lethal interaction between some mutant SUP45 and SUP35 alleles
TEF3, TEF4 and TEF5 extra copies suppress synthetic lethal interaction between the sup45-sl23ts and SUP35-C mutant alleles Earlier, we have identified mutations in the SUP45 gene which manifest lethality in combination with the SUP35C allele, which encodes eRF3 lacking the inessential N-terminal region
Summary
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. Termination of translation of mRNA is governed by stop codons in the ribosomal A-site and polypeptide chain release factors of two classes. Class I release factors RF1 and RF2 in bacteria recognize UAA/UAG and UAA/UGA stop codons, respectively, whereas eukaryotes employ only one such factor, eRF1, which is able to decode all three nonsense codons [1]. Translation termination is stimulated by class II release factors, RF3 in bacteria, and eRF3 in eukaryotes. In the yeast Saccharomyces cerevisiae eRF1 and eRF3 are encoded by the essential SUP45 and SUP35 genes
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