An eIF5/eIF2 complex antagonizes guanine nucleotide exchange by eIF2B during translation initiation

Singh, Chingakham Ranjit; Lee, Bumjun; Udagawa, Tsuyoshi; Mohammad-Qureshi, Sarah S.; Yamamoto, Yasufumi; Pavitt, Graham D.; Asano, Katsura

doi:10.1038/sj.emboj.7601339

Cited by 87 publications

(132 citation statements)

References 30 publications

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“…However, the eIF2 Á GDP/eIF5 complexes identified by Singh et al (2006) likely differ from those described here, which contain tRNA i Met and accumulate under conditions of guanine nucleotide depletion where GDP is undetectable.…”

Section: Resultscontrasting

confidence: 52%

“…Nearly one-half of the eIF2 in yeast cells, presumably in its GDP-bound state, forms a complex with eIF5, which appears to antagonize GTP exchange on eIF2-GDP to render eIF2 recycling rate limiting for translation initiation (Singh et al 2006); this complex insures an effective inhibition of eIF2 recycling by eIF2B when eIF2a is phosphorylated by Gcn2 ( Jennings and Pavitt 2010). However, the eIF2 Á GDP/eIF5 complexes identified by Singh et al (2006) likely differ from those described here, which contain tRNA i Met and accumulate under conditions of guanine nucleotide depletion where GDP is undetectable.…”

Section: Resultsmentioning

confidence: 99%

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Guanine Nucleotide Pool Imbalance Impairs Multiple Steps of Protein Synthesis and Disrupts GCN4 Translational Control in Saccharomyces cerevisiae

et al. 2011

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Purine nucleotides are structural components of the genetic material, function as phosphate donors, participate in cellular signaling, are cofactors in enzymatic reactions, and constitute the main carriers of cellular energy. Thus, imbalances in A/G nucleotide biosynthesis affect nearly the whole cellular metabolism and must be tightly regulated. We have identified a substitution mutation (G388D) that reduces the activity of the GMP synthase Gua1 in budding yeast and the total G-nucleotide pool, leading to precipitous reductions in the GDP/GTP ratio and ATP level in vivo. gua1-G388D strongly reduces the rate of growth, impairs general protein synthesis, and derepresses translation of GCN4 mRNA, encoding a transcriptional activator of diverse amino acid biosynthetic enzymes. Although processing of pre-tRNA i Met and other tRNA precursors, and the aminoacylation of tRNA iMet are also strongly impaired in gua1-G388D cells, tRNA i GTP complex (TC) and the multifactor complex (MFC) required for translation initiation accumulate $10-fold in gua1-G388D cells and, to a lesser extent, in wild-type (WT) cells treated with 6-azauracil (6AU). Consistently, addition of an external supply of guanine reverts all the phenotypes of gua1-G388D cells, but not those of gua1-G388D Dhpt1 mutants unable to refill the internal GMP pool through the salvage pathway. These and other findings suggest that a defect in guanine nucleotide biosynthesis evokes a reduction in the rate of general protein synthesis by impairing multiple steps of the process, disrupts the gene-specific reinitiation mechanism for translation of GCN4 mRNA and has far-reaching effects in cell biology and metabolism.

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Section: Resultscontrasting

confidence: 52%

Section: Resultsmentioning

confidence: 99%

Guanine Nucleotide Pool Imbalance Impairs Multiple Steps of Protein Synthesis and Disrupts GCN4 Translational Control in Saccharomyces cerevisiae

et al. 2011

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“…Recognition of the start codon during scanning triggers the release or transfer of eIF1 to a new site on the 48S complex, and this is coupled with the release of P i and eIF2-GDP, which may be associated with eIF5 (37). The eIF1A remains bound in the A site of the ribosome and serves as a docking site for eIF5B.…”

Section: Discussionmentioning

confidence: 99%

Coupled Release of Eukaryotic Translation Initiation Factors 5B and 1A from 80S Ribosomes following Subunit Joining

Fringer

Acker

Fekete

et al. 2007

Molecular and Cellular Biology

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The translation initiation GTPase eukaryotic translation initiation factor 5B (eIF5B) binds to the factor eIF1A and catalyzes ribosomal subunit joining in vitro. We show that rapid depletion of eIF5B in Saccharomyces cerevisiae results in the accumulation of eIF1A and mRNA on 40S subunits in vivo, consistent with a defect in subunit joining. Substituting Ala for the last five residues in eIF1A (eIF1A-5A) impairs eIF5B binding to eIF1A in cell extracts and to 40S complexes in vivo. Consistently, overexpression of eIF5B suppresses the growth and translation initiation defects in yeast expressing eIF1A-5A, indicating that eIF1A helps recruit eIF5B to the 40S subunit prior to subunit joining. The GTPase-deficient eIF5B-T439A mutant accumulated on 80S complexes in vivo and was retained along with eIF1A on 80S complexes formed in vitro. Likewise, eIF5B and eIF1A remained associated with 80S complexes formed in the presence of nonhydrolyzable GDPNP, whereas these factors were released from the 80S complexes in assays containing GTP. We propose that eIF1A facilitates the binding of eIF5B to the 40S subunit to promote subunit joining. Following 80S complex formation, GTP hydrolysis by eIF5B enables the release of both eIF5B and eIF1A, and the ribosome enters the elongation phase of protein synthesis.The initiation of protein synthesis in eukaryotes is a complex series of events orchestrated by initiation factors (eIFs). In vitro studies using purified translation initiation factors have led to the elucidation of the translation initiation pathway in which the different factors associate with the 40S ribosomal subunit and guide the binding of MettRNA i Met and mRNA. While the essential in vitro functions of the different factors are well established, the precise timing of factor binding to and release from the ribosome is less well understood. Moreover, not all of the in vitrodefined functions of the factors have been confirmed in vivo. The first step in translation initiation involves the binding of factor eIF2 to GTP and Met-tRNA i Met forming a ternary complex. The ternary complex along with factors eIF1, eIF1A, eIF3, and eIF5 binds to the 40S ribosome, forming the 43S complex (reviewed in reference 16). The 43S complex then binds to an mRNA near the 5Ј cap, forming a 48S complex that scans along the mRNA in a 3Ј direction in search of an AUG start codon. In the 48S complex, some of the eIF2-GTP is hydrolyzed to eIF2-GDP ϩ P i (2). Upon AUG codon recognition, GTP hydrolysis is completed, and P i is released, converting the 48S complex from an open to a closed complex with Met-tRNA i Met in the P site of the 40S subunit (29). The release of P i from the 48S complex appears to be coupled with displacement of eIF1 from its binding site near the P site (2,22). In addition, the majority of eIF2 either dissociates from or repositions on the 48S complex following AUG codon recognition (32). Intriguingly, factors eIF3, eIF1, and eIF1A appear to be retained on the 48S complex following eIF2 release (38

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“…eIF5 binds both eIF2-GDP and TC with identical high affinity (eIF2-GDP K d = 23 6 9 nM, TC K d = 23 6 5 nM) (Algire et al 2005), and cells contain an abundant fraction of inactive eIF2-GDP/eIF5 complexes that are thought to be released from the 48S PIC following AUG recognition (Singh et al 2006). eIF5 lowers the rate of spontaneous GDP release from eIF2 over a range of Mg 2+ concentrations (Jennings and Pavitt 2010a), and this GDI activity requires the eIF5 CTD and the region linking it to the NTD.…”

Section: Gdp Dissociation Inhibitor Function Of Eif5mentioning

confidence: 99%

Mechanism and Regulation of Protein Synthesis in Saccharomyces cerevisiae

2016

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In this review, we provide an overview of protein synthesis in the yeast Saccharomyces cerevisiae. The mechanism of protein synthesis is well conserved between yeast and other eukaryotes, and molecular genetic studies in budding yeast have provided critical insights into the fundamental process of translation as well as its regulation. The review focuses on the initiation and elongation phases of protein synthesis with descriptions of the roles of translation initiation and elongation factors that assist the ribosome in binding the messenger RNA (mRNA), selecting the start codon, and synthesizing the polypeptide. We also examine mechanisms of translational control highlighting the mRNA cap-binding proteins and the regulation of GCN4 and CPA1 mRNAs.

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An eIF5/eIF2 complex antagonizes guanine nucleotide exchange by eIF2B during translation initiation

Cited by 87 publications

References 30 publications

Guanine Nucleotide Pool Imbalance Impairs Multiple Steps of Protein Synthesis and Disrupts GCN4 Translational Control in Saccharomyces cerevisiae

Guanine Nucleotide Pool Imbalance Impairs Multiple Steps of Protein Synthesis and Disrupts GCN4 Translational Control in Saccharomyces cerevisiae

Coupled Release of Eukaryotic Translation Initiation Factors 5B and 1A from 80S Ribosomes following Subunit Joining

Mechanism and Regulation of Protein Synthesis in Saccharomyces cerevisiae

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