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Papaspyropoulos A, Hazapis O, Altulea A, Polyzou A, Verginis P, Evangelou K, Fousteri M, Papantonis A, Demaria M, Gorgoulis V. Decoding of translation-regulating entities reveals heterogeneous translation deficiency patterns in cellular senescence. Aging Cell 2023; 22:e13893. [PMID: 37547972 PMCID: PMC10497830 DOI: 10.1111/acel.13893] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Accepted: 05/04/2023] [Indexed: 08/08/2023] Open
Abstract
Cellular senescence constitutes a generally irreversible proliferation barrier, accompanied by macromolecular damage and metabolic rewiring. Several senescence types have been identified based on the initiating stimulus, such as replicative (RS), stress-induced (SIS) and oncogene-induced senescence (OIS). These senescence subtypes are heterogeneous and often develop subset-specific phenotypes. Reduced protein synthesis is considered a senescence hallmark, but whether this trait pertains to various senescence subtypes and if distinct molecular mechanisms are involved remain largely unknown. Here, we analyze large published or experimentally produced RNA-seq and Ribo-seq datasets to determine whether major translation-regulating entities such as ribosome stalling, the presence of uORFs/dORFs and IRES elements may differentially contribute to translation deficiency in senescence subsets. We show that translation-regulating mechanisms may not be directly relevant to RS, however uORFs are significantly enriched in SIS. Interestingly, ribosome stalling, uORF/dORF patterns and IRES elements comprise predominant mechanisms upon OIS, strongly correlating with Notch pathway activation. Our study provides for the first time evidence that major translation dysregulation mechanisms/patterns occur during cellular senescence, but at different rates depending on the stimulus type. The degree at which those mechanisms accumulate directly correlates with translation deficiency levels. Our thorough analysis contributes to elucidating crucial and so far unknown differences in the translation machinery between senescence subsets.
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Affiliation(s)
- Angelos Papaspyropoulos
- Molecular Carcinogenesis Group, Department of Histology and Embryology, School of MedicineNational Kapodistrian University of Athens (NKUA)AthensGreece
- Biomedical Research FoundationAcademy of AthensAthensGreece
| | - Orsalia Hazapis
- Molecular Carcinogenesis Group, Department of Histology and Embryology, School of MedicineNational Kapodistrian University of Athens (NKUA)AthensGreece
| | - Abdullah Altulea
- European Research Institute for the Biology of Ageing (ERIBA)University Medical Center GroningenGroningenThe Netherlands
| | - Aikaterini Polyzou
- Molecular Carcinogenesis Group, Department of Histology and Embryology, School of MedicineNational Kapodistrian University of Athens (NKUA)AthensGreece
| | | | - Konstantinos Evangelou
- Molecular Carcinogenesis Group, Department of Histology and Embryology, School of MedicineNational Kapodistrian University of Athens (NKUA)AthensGreece
| | - Maria Fousteri
- Institute for Fundamental Biomedical ResearchBiomedical Sciences Research Center “Alexander Fleming”VariGreece
| | - Argyris Papantonis
- Institute of PathologyUniversity Medical Center GöttingenGöttingenGermany
- Center for Molecular Medicine CologneUniversity of CologneCologneGermany
| | - Marco Demaria
- European Research Institute for the Biology of Ageing (ERIBA)University Medical Center GroningenGroningenThe Netherlands
| | - Vassilis Gorgoulis
- Molecular Carcinogenesis Group, Department of Histology and Embryology, School of MedicineNational Kapodistrian University of Athens (NKUA)AthensGreece
- Biomedical Research FoundationAcademy of AthensAthensGreece
- Clinical Molecular PathologyMedical School, University of DundeeDundeeUK
- Molecular and Clinical Cancer Sciences, Manchester Cancer Research Centre, Manchester Academic Health Sciences CentreUniversity of ManchesterManchesterUK
- Center for New Biotechnologies and Precision MedicineMedical School, National and Kapodistrian University of AthensAthensGreece
- Faculty of Health and Medical SciencesUniversity of SurreySurreyUK
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2
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Terenin IM, Akulich KA, Andreev DE, Polyanskaya SA, Shatsky IN, Dmitriev SE. Sliding of a 43S ribosomal complex from the recognized AUG codon triggered by a delay in eIF2-bound GTP hydrolysis. Nucleic Acids Res 2016; 44:1882-93. [PMID: 26717981 PMCID: PMC4770231 DOI: 10.1093/nar/gkv1514] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Revised: 12/16/2015] [Accepted: 12/17/2015] [Indexed: 02/05/2023] Open
Abstract
During eukaryotic translation initiation, 43S ribosomal complex scans mRNA leader unless an AUG codon in an appropriate context is found. Establishing the stable codon-anticodon base-pairing traps the ribosome on the initiator codon and triggers structural rearrangements, which lead to Pi release from the eIF2-bound GTP. It is generally accepted that AUG recognition by the scanning 43S complex sets the final point in the process of start codon selection, while latter stages do not contribute to this process. Here we use translation reconstitution approach and kinetic toe-printing assay to show that after the 48S complex is formed on an AUG codon, in case GTP hydrolysis is impaired, the ribosomal subunit is capable to resume scanning and slides downstream to the next AUG. In contrast to leaky scanning, this sliding is not limited to AUGs in poor nucleotide contexts and occurs after a relatively long pause at the recognized AUG. Thus, recognition of an AUG per se does not inevitably lead to this codon being selected for initiation of protein synthesis. Instead, it is eIF5-induced GTP hydrolysis and Pi release that irreversibly trap the 48S complex, and this complex is further stabilized by eIF5B and 60S joining.
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Affiliation(s)
- Ilya M Terenin
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow 119991, Russia
| | - Kseniya A Akulich
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia School of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow 119234, Russia
| | - Dmitry E Andreev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia
| | - Sofya A Polyanskaya
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia Department of Molecular Biology, Biological Faculty, Lomonosov Moscow State University, Moscow 119234, Russia
| | - Ivan N Shatsky
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia
| | - Sergey E Dmitriev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow 119991, Russia Department of Biochemistry, Biological Faculty, Lomonosov Moscow State University, Moscow 119234, Russia
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3
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Liberman N, Gandin V, Svitkin YV, David M, Virgili G, Jaramillo M, Holcik M, Nagar B, Kimchi A, Sonenberg N. DAP5 associates with eIF2β and eIF4AI to promote Internal Ribosome Entry Site driven translation. Nucleic Acids Res 2015; 43:3764-75. [PMID: 25779044 PMCID: PMC4402527 DOI: 10.1093/nar/gkv205] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Revised: 02/26/2015] [Accepted: 02/27/2015] [Indexed: 12/14/2022] Open
Abstract
Initiation is a highly regulated rate-limiting step of mRNA translation. During cap-dependent translation, the cap-binding protein eIF4E recruits the mRNA to the ribosome. Specific elements in the 5'UTR of some mRNAs referred to as Internal Ribosome Entry Sites (IRESes) allow direct association of the mRNA with the ribosome without the requirement for eIF4E. Cap-independent initiation permits translation of a subset of cellular and viral mRNAs under conditions wherein cap-dependent translation is inhibited, such as stress, mitosis and viral infection. DAP5 is an eIF4G homolog that has been proposed to regulate both cap-dependent and cap-independent translation. Herein, we demonstrate that DAP5 associates with eIF2β and eIF4AI to stimulate IRES-dependent translation of cellular mRNAs. In contrast, DAP5 is dispensable for cap-dependent translation. These findings provide the first mechanistic insights into the function of DAP5 as a selective regulator of cap-independent translation.
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Affiliation(s)
- Noa Liberman
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Valentina Gandin
- Department of Biochemistry, McGill University, Montréal, Québec H3A 1A3, Canada Rosalind and Morris Goodman Cancer Centre, Montréal, Québec H3A 1A3, Canada
| | - Yuri V Svitkin
- Department of Biochemistry, McGill University, Montréal, Québec H3A 1A3, Canada Rosalind and Morris Goodman Cancer Centre, Montréal, Québec H3A 1A3, Canada
| | - Maya David
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Geneviève Virgili
- Department of Biochemistry, McGill University, Montréal, Québec H3A 1A3, Canada Groupe de Recherche Axé sur la Structure des Protéines, Montréal, Québec H3A 1A3, Canada
| | - Maritza Jaramillo
- Department of Biochemistry, McGill University, Montréal, Québec H3A 1A3, Canada Rosalind and Morris Goodman Cancer Centre, Montréal, Québec H3A 1A3, Canada
| | - Martin Holcik
- Apoptosis Research Centre, Children's Hospital of Eastern Ontario Research Institute, Ottawa, Ontario K1N 6N5, Canada
| | - Bhushan Nagar
- Department of Biochemistry, McGill University, Montréal, Québec H3A 1A3, Canada Groupe de Recherche Axé sur la Structure des Protéines, Montréal, Québec H3A 1A3, Canada
| | - Adi Kimchi
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Nahum Sonenberg
- Department of Biochemistry, McGill University, Montréal, Québec H3A 1A3, Canada Rosalind and Morris Goodman Cancer Centre, Montréal, Québec H3A 1A3, Canada
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4
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Naarmann IS, Harnisch C, Müller-Newen G, Urlaub H, Ostareck-Lederer A, Ostareck DH. DDX6 recruits translational silenced human reticulocyte 15-lipoxygenase mRNA to RNP granules. RNA (NEW YORK, N.Y.) 2010; 16:2189-204. [PMID: 20884783 PMCID: PMC2957058 DOI: 10.1261/rna.2211110] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2010] [Accepted: 08/11/2010] [Indexed: 05/29/2023]
Abstract
Erythroid precursor cells lose the capacity for mRNA synthesis due to exclusion of the nucleus during maturation. Therefore, the stability and translation of mRNAs that code for specific proteins, which function in late stages of maturation when reticulocytes become erythrocytes, are controlled tightly. Reticulocyte 15-lipoxygenase (r15-LOX) initiates the breakdown of mitochondria in mature reticulocytes. Through the temporal restriction of mRNA translation, the synthesis of r15-LOX is prevented in premature cells. The enzyme is synthesized only in mature reticulocytes, although r15-LOX mRNA is already present in erythroid precursor cells. Translation of r15-LOX mRNA is inhibited by hnRNP K and hnRNP E1, which bind to the differentiation control element (DICE) in its 3' untranslated region (3'UTR). The hnRNP K/E1-DICE complex interferes with the joining of the 60S ribosomal subunit to the 40S subunit at the AUG. We took advantage of the inducible human erythroid K562 cell system that fully recapitulates this process to identify so far unknown factors, which are critical for DICE-dependent translational regulation. Applying RNA chromatography with the DICE as bait combined with hnRNP K immunoprecipitation, we specifically purified the DEAD-box RNA helicase 6 (DDX6) that interacts with hnRNP K and hnRNP E1 in a DICE-dependent manner. Employing RNA interference and fluorescence in situ hybridization, we show that DDX6 colocalizes with endogenous human (h)r15-LOX mRNA to P-body-like RNP granules, from which 60S ribosomal subunits are excluded. Our data suggest that in premature erythroid cells translational silencing of hr15-LOX mRNA is maintained by DDX6 mediated storage in these RNP granules.
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Affiliation(s)
- Isabel S Naarmann
- Department of Intensive Care, Experimental Research Unit, University Hospital, RWTH Aachen University, 52074 Aachen, Germany
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5
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WOODLEY CL, ROYCHOWDHURY M, OLSEN KW, WAHBA AJ, MACRAE TH. Protein Synthesis in Brine Shrimp Embryos. ACTA ACUST UNITED AC 2005. [DOI: 10.1111/j.1432-1033.1981.tb06371.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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6
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Kedersha N, Cho MR, Li W, Yacono PW, Chen S, Gilks N, Golan DE, Anderson P. Dynamic shuttling of TIA-1 accompanies the recruitment of mRNA to mammalian stress granules. J Cell Biol 2000; 151:1257-68. [PMID: 11121440 PMCID: PMC2190599 DOI: 10.1083/jcb.151.6.1257] [Citation(s) in RCA: 612] [Impact Index Per Article: 25.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2000] [Accepted: 10/24/2000] [Indexed: 11/22/2022] Open
Abstract
Mammalian stress granules (SGs) harbor untranslated mRNAs that accumulate in cells exposed to environmental stress. Drugs that stabilize polysomes (emetine) inhibit the assembly of SGs, whereas drugs that destabilize polysomes (puromycin) promote the assembly of SGs. Moreover, emetine dissolves preformed SGs as it promotes the assembly of polysomes, suggesting that these mRNP species (i.e., SGs and polysomes) exist in equilibrium. We used green flourescent protein-tagged SG-associated RNA-binding proteins (specifically, TIA-1 and poly[A] binding protein [PABP-I]) to monitor SG assembly, disassembly, and turnover in live cells. Fluorescence recovery after photobleaching shows that both TIA-1 and PABP-I rapidly and continuously shuttle in and out of SGs, indicating that the assembly of SGs is a highly dynamic process. This unexpected result leads us to propose that mammalian SGs are sites at which untranslated mRNAs are sorted and processed for either reinitiation, degradation, or packaging into stable nonpolysomal mRNP complexes. A truncation mutant of TIA-1 (TIA-1DeltaRRM), which acts as a transdominant inhibitor of SG assembly, promotes the expression of cotransfected reporter genes in COS transfectants, suggesting that this process of mRNA triage might, directly or indirectly, influence protein expression.
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Affiliation(s)
- Nancy Kedersha
- Division of Rheumatology and Immunology, Harvard Medical School, Hematology Division, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | - Michael R. Cho
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Hematology Division, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | - Wei Li
- Division of Rheumatology and Immunology, Harvard Medical School, Hematology Division, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | - Patrick W. Yacono
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Hematology Division, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | - Samantha Chen
- Division of Rheumatology and Immunology, Harvard Medical School, Hematology Division, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | - Natalie Gilks
- Division of Rheumatology and Immunology, Harvard Medical School, Hematology Division, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | - David E. Golan
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Hematology Division, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | - Paul Anderson
- Division of Rheumatology and Immunology, Harvard Medical School, Hematology Division, Brigham and Women's Hospital, Boston, Massachusetts 02115
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7
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Greenberg JR, Phan L, Gu Z, deSilva A, Apolito C, Sherman F, Hinnebusch AG, Goldfarb DS. Nip1p associates with 40 S ribosomes and the Prt1p subunit of eukaryotic initiation factor 3 and is required for efficient translation initiation. J Biol Chem 1998; 273:23485-94. [PMID: 9722586 DOI: 10.1074/jbc.273.36.23485] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nip1p is an essential Saccharomyces cerevisiae protein that was identified in a screen for temperature conditional (ts) mutants exhibiting defects in nuclear transport. New results indicate that Nip1p has a primary role in translation initiation. Polysome profiles indicate that cells depleted of Nip1p and nip1-1 cells are defective in translation initiation, a conclusion that is supported by a reduced rate of protein synthesis in Nip1p-depleted cells. Nip1p cosediments with free 40 S ribosomal subunits and polysomal preinitiation complexes, but not with free or elongating 80 S ribosomes or 60 S subunits. Nip1p can be isolated in an about 670-kDa complex containing polyhistidine-tagged Prt1p, a subunit of translation initiation factor 3, by binding to Ni2+-NTA-agarose beads in a manner completely dependent on the tagged form of Prt1p. The nip1-1 ts growth defect was suppressed by the deletion of the ribosomal protein, RPL46. Also, nip1-1 mutant cells are hypersensitive to paromomycin. These results suggest that Nip1p is a subunit of eukaryotic initiation factor 3 required for efficient translation initiation.
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Affiliation(s)
- J R Greenberg
- Department of Biology, University of Rochester, Rochester, New York 14627, USA
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8
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Phan L, Zhang X, Asano K, Anderson J, Vornlocher HP, Greenberg JR, Qin J, Hinnebusch AG. Identification of a translation initiation factor 3 (eIF3) core complex, conserved in yeast and mammals, that interacts with eIF5. Mol Cell Biol 1998; 18:4935-46. [PMID: 9671501 PMCID: PMC109077 DOI: 10.1128/mcb.18.8.4935] [Citation(s) in RCA: 157] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/1998] [Accepted: 05/11/1998] [Indexed: 02/08/2023] Open
Abstract
Only five of the nine subunits of human eukaryotic translation initiation factor 3 (eIF3) have recognizable homologs encoded in the Saccharomyces cerevisiae genome, and only two of these (Prt1p and Tif34p) were identified previously as subunits of yeast eIF3. We purified a polyhistidine-tagged form of Prt1p (His-Prt1p) by Ni2+ affinity and gel filtration chromatography and obtained a complex of approximately 600 kDa composed of six polypeptides whose copurification was completely dependent on the polyhistidine tag on His-Prt1p. All five polypeptides associated with His-Prt1p were identified by mass spectrometry, and four were found to be the other putative homologs of human eIF3 subunits encoded in S. cerevisiae: YBR079c/Tif32p, Nip1p, Tif34p, and YDR429c/Tif35p. The fifth Prt1p-associated protein was eIF5, an initiation factor not previously known to interact with eIF3. The purified complex could rescue Met-tRNAiMet binding to 40S ribosomes in defective extracts from a prt1 mutant or extracts from which Nip1p had been depleted, indicating that it possesses a known biochemical activity of eIF3. These findings suggest that Tif32p, Nip1p, Prt1p, Tif34p, and Tif35p comprise an eIF3 core complex, conserved between yeast and mammals, that stably interacts with eIF5. Nip1p bound to eIF5 in yeast two-hybrid and in vitro protein binding assays. Interestingly, Sui1p also interacts with Nip1p, and both eIF5 and Sui1p have been implicated in accurate recognition of the AUG start codon. Thus, eIF5 and Sui1p may be recruited to the 40S ribosomes through physical interactions with the Nip1p subunit of eIF3.
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Affiliation(s)
- L Phan
- Laboratory of Eukaryotic Gene Regulation, National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA
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9
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Kimball SR, Fabian JR, Pavitt GD, Hinnebusch AG, Jefferson LS. Regulation of guanine nucleotide exchange through phosphorylation of eukaryotic initiation factor eIF2alpha. Role of the alpha- and delta-subunits of eiF2b. J Biol Chem 1998; 273:12841-5. [PMID: 9582312 DOI: 10.1074/jbc.273.21.12841] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The guanine nucleotide exchange activity of eIF2B plays a key regulatory role in the translation initiation phase of protein synthesis. The activity is markedly inhibited when the substrate, i. e. eIF2, is phosphorylated on Ser51 of its alpha-subunit. Genetic studies in yeast implicate the alpha-, beta-, and delta-subunits of eIF2B in mediating the inhibition by substrate phosphorylation. However, the mechanism involved in the inhibition has not been defined biochemically. In the present study, we have coexpressed the five subunits of rat eIF2B in Sf9 cells using the baculovirus system and have purified the recombinant holoprotein to >90% homogeneity. We have also expressed and purified a four-subunit eIF2B complex lacking the alpha-subunit. Both the five- and four-subunit forms of eIF2B exhibit similar rates of guanine nucleotide exchange activity using unphosphorylated eIF2 as substrate. The five-subunit form is inhibited by preincubation with phosphorylated eIF2 (eIF2(alphaP)) and exhibits little exchange activity when eIF2(alphaP) is used as substrate. In contrast, eIF2B lacking the alpha-subunit is insensitive to inhibition by eIF2(alphaP) and is able to exchange guanine nucleotide using eIF2(alphaP) as substrate at a faster rate compared with five-subunit eIF2B. Finally, a double point mutation in the delta-subunit of eIF2B has been identified that results in insensitivity to inhibition by eIF2(alphaP) and exhibits little exchange activity when eIF2(alphaP) is used as substrate. The results provide the first direct biochemical evidence that the alpha- and delta-subunits of eIF2B are involved in mediating the effect of substrate phosphorylation.
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Affiliation(s)
- S R Kimball
- Department of Cellular and Molecular Physiology, Pennsylvania State University, College of Medicine, Hershey, Pennsylvania 17033, USA.
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10
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Das S, Maiti T, Das K, Maitra U. Specific interaction of eukaryotic translation initiation factor 5 (eIF5) with the beta-subunit of eIF2. J Biol Chem 1997; 272:31712-8. [PMID: 9395514 DOI: 10.1074/jbc.272.50.31712] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Eukaryotic translation initiation factor 5 (eIF5) interacts with the 40 S initiation complex (40 S.mRNA. eIF3.Met-tRNAf.eIF2.GTP) and mediates hydrolysis of the bound GTP. To characterize the molecular interactions involved in eIF5 function, we have used 32P-labeled recombinant rat eIF5 as a probe in filter overlay assay to identify eIF5-interacting proteins in crude initiation factor preparations. We observed that eIF5 specifically interacted with the beta subunit of initiation factor eIF2. No other initiation factors including the gamma subunit of eIF2 tested positive in this assay. Furthermore, both yeast and mammalian eIF5 bind to the beta subunit of either mammalian or yeast eIF2. Binding analysis with human eIF2beta deletion mutants expressed in Escherichia coli identified a 22-amino acid domain, between amino acids 68 and 89, as the primary eIF5-binding region of eIF2beta. These results along with our earlier observations that (a) eIF5 neither binds nor hydrolyzes free GTP or GTP bound as Met-tRNAf.eIF2.GTP ternary complex, and (b) eIF5 forms a specific complex with eIF2 suggests that the specific interaction between eIF5 and the beta subunit of eIF2 may be critical for the hydrolysis of GTP during translation initiation.
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Affiliation(s)
- S Das
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA
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11
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Maiti T, Maitra U. Characterization of translation initiation factor 5 (eIF5) from Saccharomyces cerevisiae. Functional homology with mammalian eIF5 and the effect of depletion of eIF5 on protein synthesis in vivo and in vitro. J Biol Chem 1997; 272:18333-40. [PMID: 9218474 DOI: 10.1074/jbc.272.29.18333] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Eukaryotic translation initiation factor 5 (eIF5) interacts in vitro with the 40 S initiation complex (40 S.AUG.Met-tRNAf.eIF2.GTP) to mediate the hydrolysis of ribosome-bound GTP. In Saccharomyces cerevisiae, eIF5 is encoded by a single copy essential gene, TIF5, that encodes a protein of 45,346 daltons. To understand the function of eIF5 in vivo, we constructed a conditional mutant yeast strain in which a functional but a rapidly degradable form of eIF5 fusion protein was synthesized from the repressible GAL promoter. Depletion of eIF5 from this mutant yeast strain resulted in inhibition of both cell growth and the rate of in vivo protein synthesis. Analysis of the polysome profiles of eIF5-depleted cells showed greatly diminished polysomes with simultaneous increase in free ribosomes. Furthermore, lysates of cells depleted of eIF5 were dependent on exogenously added yeast eIF5 for efficient translation of mRNAs in vitro. This is the first demonstration that the TIF5 gene encodes a protein involved in initiation of translation in eukaryotic cells. Additionally, we show that rat eIF5 can functionally substitute yeast eIF5 in translation of mRNAs in vitro as well as in complementing in vivo a genetic disruption in the chromosomal copy of TIF5.
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Affiliation(s)
- T Maiti
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine of Yeshiva University, Jack and Pearl Resnick Campus, Bronx, New York 10461, USA
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12
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Pavitt GD, Yang W, Hinnebusch AG. Homologous segments in three subunits of the guanine nucleotide exchange factor eIF2B mediate translational regulation by phosphorylation of eIF2. Mol Cell Biol 1997; 17:1298-313. [PMID: 9032257 PMCID: PMC231855 DOI: 10.1128/mcb.17.3.1298] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
eIF2B is a five-subunit guanine nucleotide exchange factor that is negatively regulated by phosphorylation of the alpha subunit of its substrate, eIF2, leading to inhibition of translation initiation. To analyze this regulatory mechanism, we have characterized 29 novel mutations in the homologous eIF2B subunits encoded by GCD2, GCD7, and GCN3 that reduce or abolish inhibition of eIF2B activity by eIF2 phosphorylated on its alpha subunit [eIF2(alphaP)]. Most, if not all, of the mutations decrease sensitivity to eIF2(alphaP) without excluding GCN3, the nonessential subunit, from eIF2B; thus, all three proteins are critical for regulation of eIF2B by eIF2(alphaP). The mutations are clustered at both ends of the homologous region of each subunit, within two segments each of approximately 70 amino acids in length. Several mutations alter residues at equivalent positions in two or all three subunits. These results imply that structurally similar segments in GCD2, GCD7, and GCN3 perform related functions in eIF2B regulation. We propose that these segments form a single domain in eIF2B that makes multiple contacts with the alpha subunit of eIF2, around the phosphorylation site, allowing eIF2B to detect and respond to phosphoserine at residue 51. Most of the eIF2 is phosphorylated in certain mutants, suggesting that these substitutions allow eIF2B to accept phosphorylated eIF2 as a substrate for nucleotide exchange.
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Affiliation(s)
- G D Pavitt
- Laboratory of Eukaryotic Gene Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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13
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Si K, Das K, Maitra U. Characterization of multiple mRNAs that encode mammalian translation initiation factor 5 (eIF-5). J Biol Chem 1996; 271:16934-8. [PMID: 8663286 DOI: 10.1074/jbc.271.28.16934] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Eukaryotic translation initiation factor 5 (eIF-5) interacts with the 40 S initiation complex (40S.mRNA.MettRNAf.eIF-2.GTP) to promote the hydrolysis of bound GTP with the concomitant joining of the 60 S ribosomal subunit to the 40 S initiation complex to form a functional 80 S initiation complex. In this paper, the multiple mRNAs that encode mammalian eIF-5 have been characterized. In rat tissues, three major eIF-5 mRNAs of 3.5, 2.8, and 2.2 kilobases in length are detected. All major eIF-5 mRNAs are initiated from a single transcription initiation site, contain identical 5'-untranslated and coding regions, but differ from one another only in the length of their 3'-untranslated regions. The different lengths of the 3'-untranslated region of eIF-5 mRNAs are generated by the use of alternative polyadenylation signals. Additionally, we demonstrate tissue-specific variations in eIF-5 mRNA expression as well as preference for polyadenylation sites. These results should lead to increased understanding of the regulation of eIF-5 gene expression.
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Affiliation(s)
- K Si
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine of Yeshiva University, Jack and Pearl Resnick Campus, Bronx, New York 10461, USA
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14
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Kimball SR, Mellor H, Flowers KM, Jefferson LS. Role of translation initiation factor eIF-2B in the regulation of protein synthesis in mammalian cells. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1996; 54:165-96. [PMID: 8768075 DOI: 10.1016/s0079-6603(08)60363-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- S R Kimball
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey 17033, USA
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Koonin EV. Multidomain organization of eukaryotic guanine nucleotide exchange translation initiation factor eIF-2B subunits revealed by analysis of conserved sequence motifs. Protein Sci 1995; 4:1608-17. [PMID: 8520487 PMCID: PMC2143190 DOI: 10.1002/pro.5560040819] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Computer-assisted analysis of amino acid sequences using methods for database screening with individual sequences and with multiple alignment blocks reveals a complex multidomain organization of yeast proteins GCD6 and GCD1, and mammalian homolog of GCD6-subunits of the eukaryotic translation initiation factor eIF-2B involved in GDP/GTP exchange on eIF-2. It is shown that these proteins contain a putative nucleotide-binding domain related to a variety of nucleotidyltransferases, most of which are involved in nucleoside diphosphate-sugar formation in bacteria. Three conserved motifs, one of which appears to be a variant of the phosphate-binding site (P-loop) and another that may be considered a specific version of the Mg(2+)-binding site of NTP-utilizing enzymes, were identified in the nucleotidyltransferase-related domain. Together with the third unique motif adjacent to the the P-loop, these motifs comprise the signature of a new superfamily of nucleotide-binding domains. A domain consisting of hexapeptide amino acid repeats with a periodic distribution of bulky hydrophobic residues (isoleucine patch), which previously have been identified in bacterial acetyltransferases, is located toward the C-terminus from the nucleotidyltransferase-related domain. Finally, at the very C-termini of GCD6, eIF-2B epsilon, and two other eukaryotic translation initiation factors, eIF-4 gamma and eIF-5, there is a previously undetected, conserved domain. It is hypothesized that the nucleotidyltransferase-related domain is directly involved in the GDP/GTP exchange, whereas the C-terminal conserved domain may be involved in the interaction of eIF-2B, eIF-4 gamma, and eIF-5 with eIF-2.
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Affiliation(s)
- E V Koonin
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland 20894, USA
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Flowers KM, Kimball SR, Feldhoff RC, Hinnebusch AG, Jefferson LS. Molecular cloning and characterization of cDNA encoding the alpha subunit of the rat protein synthesis initiation factor eIF-2B. Proc Natl Acad Sci U S A 1995; 92:4274-8. [PMID: 7753796 PMCID: PMC41926 DOI: 10.1073/pnas.92.10.4274] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Eukaryotic initiation factor 2B (eIF-2B) is an essential component of the pathway of peptide-chain initiation in mammalian cells, yet little is known about its molecular structure and regulation. To investigate the structure, regulation, and interactions of the individual subunits of eIF-2B, we have begun to clone, characterize, and express the corresponding cDNAs. We report here the cloning and characterization of a 1510-bp cDNA encoding the alpha subunit of eIF-2B from a rat brain cDNA library. The cDNA contains an open reading frame of 918 bp encoding a polypeptide of 305 aa with a predicted molecular mass of 33.7 kDa. This cDNA recognizes a single RNA species approximately 1.6 kb in length on Northern blots of RNA from rat liver. The predicted amino acid sequence contains regions identical to the sequences of peptides derived from bovine liver eIF-2B alpha subunit. Expression of this cDNA in vitro yields a peptide which comigrates with natural eIF-2B alpha in SDS/polyacrylamide gels. The predicted amino acid sequence exhibits 42% identity to that deduced for the Saccharomyces cerevisiae GCN3 protein, the smallest subunit of yeast eIF-2B. In addition, expression of the rat cDNA in yeast functionally complements a gcn3 deletion for the inability to induce histidine biosynthetic genes under the control of GCN4. These results strongly support the hypothesis that mammalian eIF-2 alpha and GCN3 are homologues. Southern blots indicate that the eIF-2B alpha cDNA also recognizes genomic DNA fragments from several other species, suggesting significant homology between the rat eIF-2B alpha gene and that from other species.
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Affiliation(s)
- K M Flowers
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey 17033, USA
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17
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Chevesich J, Chaudhuri J, Maitra U. Characterization of mammalian translation initiation factor 5 (eIF-5). Demonstration that eIF-5 is a phosphoprotein and is present in cells as a single molecular form of apparent M(r) 58,000. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(20)80775-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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18
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Das K, Chevesich J, Maitra U. Molecular cloning and expression of cDNA for mammalian translation initiation factor 5. Proc Natl Acad Sci U S A 1993; 90:3058-62. [PMID: 8464924 PMCID: PMC46236 DOI: 10.1073/pnas.90.7.3058] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Eukaryotic translation initiation factor 5 (eIF-5) catalyzes the hydrolysis of GTP bound to the 40S ribosomal initiation complex (40S.AUG.Met-tRNAf-eIF-2.GTP) with the subsequent joining of a 60S ribosomal subunit resulting in the formation of a functional 80S initiation complex. A rat cDNA that encodes eIF-5 has been isolated and expressed in Escherichia coli to yield a catalytically active eIF-5 protein. The 3.55-kb cDNA encodes a protein of 429 amino acids (calculated M(r) 48,926) with properties that are similar to eIF-5 isolated from rabbit reticulocyte lysates. The deduced amino acid sequence of eIF-5 contains sequence motifs characteristic of proteins of the GTPase superfamily.
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Affiliation(s)
- K Das
- Department of Developmental Biology and Cancer, Albert Einstein College of Medicine, Bronx, NY 10461
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19
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Dholakia J, Xu Z, Hille M, Wahba A. Purification and characterization of sea urchin initiation factor 2. The requirement of guanine nucleotide exchange factor for the release of eukaryotic polypeptide chain initiation factor 2-bound GDP. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)30660-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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20
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Dholakia J, Francis B, Haley B, Wahba A. Photoaffinity labeling of the rabbit reticulocyte guanine nucleotide exchange factor and eukaryotic initiation factor 2 with 8-azidopurine nucleotides. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)47111-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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21
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Dholakia JN, Wahba AJ. Mechanism of the Nucleotide Exchange Reaction in Eukaryotic Polypeptide Chain Initiation. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(17)31293-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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22
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Dholakia JN, Wahba AJ. Phosphorylation of the guanine nucleotide exchange factor from rabbit reticulocytes regulates its activity in polypeptide chain initiation. Proc Natl Acad Sci U S A 1988; 85:51-4. [PMID: 3422426 PMCID: PMC279479 DOI: 10.1073/pnas.85.1.51] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
We have demonstrated that the purified guanine nine nucleotide exchange factor (GEF) may be isolated as a complex with NADPH. Complete inhibition of the GEF-catalyzed exchange of eukaryotic initiation factor 2-bound GDP for GTP was observed in the presence of either 0.5-0.75 mM NAD+ or NADP+. Incubation of GEF with ATP results in the phosphorylation of its Mr 82,000 polypeptide. This phosphorylation is strongly inhibited by heparin but is not affected by heme or H8 (N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride), an inhibitor of cAMP- and cGMP-dependent protein kinases and protein kinase C. The purification of GEF was modified to eliminate any contaminating kinase activity and the isolated protein appears to be homogeneous as judged by NaDodSO4/polyacrylamide gel electrophoresis and silver staining. The Mr 82,000 subunit of GEF is phosphorylated only upon addition of ATP and casein kinase II. The extent of phosphorylation is approximately equal to 0.55 mol of phosphate per mol of GEF, and this results in a 2.3-fold increase in the guanine nucleotide exchange activity. Following treatment of the phosphorylated GEF with alkaline phosphatase, the activity of the protein is reduced by a factor of 5. Rephosphorylation of GEF increases its specific activity to that of the phosphorylated protein. The results of this study suggest that phosphorylation/dephosphorylation of GEF plays a role in regulating polypeptide chain initiation.
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Affiliation(s)
- J N Dholakia
- Department of Biochemistry, University of Mississippi Medical Center, Jackson 39216-4505
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23
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Evidence that phosphorylation of eIF-2(alpha) prevents the eIF-2B-mediated dissociation of eIF-2 X GDP from the 60 S subunit of complete initiation complexes. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)48329-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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24
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London IM, Levin DH, Matts RL, Thomas NSB, Petryshyn R, Chen JJ. 12 Regulation of Protein Synthesis. CONTROL BY PHOSPHORYLATION PART B - SPECIFIC ENZYMES (II) BIOLOGICAL PROCESSES 1987. [DOI: 10.1016/s1874-6047(08)60263-2] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Dholakia JN, Mueser TC, Woodley CL, Parkhurst LJ, Wahba AJ. The association of NADPH with the guanine nucleotide exchange factor from rabbit reticulocytes: a role of pyridine dinucleotides in eukaryotic polypeptide chain initiation. Proc Natl Acad Sci U S A 1986; 83:6746-50. [PMID: 3462724 PMCID: PMC386586 DOI: 10.1073/pnas.83.18.6746] [Citation(s) in RCA: 65] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The guanine nucleotide exchange factor (GEF) was purified to apparent homogeneity from postribosomal supernatants of rabbit reticulocytes by chromatography on DEAE-cellulose and phosphocellulose, fractionation by glycerol gradients, and chromatography on Mono S and Mono Q (Pharmacia). At the Mono S step GEF is isolated as a complex with the eukaryotic polypeptide chain initiation factor 2 (eIF-2) and is separated from this factor by column chromatography on Mono Q. An emission spectrum characteristic of a reduced pyridine dinucleotide was observed when GEF was subjected to fluorescence analysis. By both coupled enzymatic analysis and chromatography on reverse-phase or Mono Q columns, the bound dinucleotide associated with GEF was determined to be NADPH. The GEF-catalyzed exchange of eIF-2-bound GDP for GTP was markedly inhibited by NAD+ and NADP+. This inhibition was not observed in the presence of equimolar concentrations of NADPH. Similarly, the stimulation of ternary complex (eIF-2 X GTP X Met-tRNAf) formation by GEF in the presence of 1 mM Mg2+ was abolished in the presence of oxidized pyridine dinucleotide. These results demonstrate that pyridine dinucleotides may be directly involved in the regulation of polypeptide chain initiation by acting as allosteric regulators of GEF activity.
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26
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27
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Gupta NK, Chakrabarti D. Mechanism of peptide chain initiation in animal cells: a reevaluation. Mol Cell Biochem 1986; 70:105-11. [PMID: 3724748 DOI: 10.1007/bf00229425] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Despite numerous reports from several laboratories, the precise mechanism of peptide chain initiation in animal cells and the roles of different factors involved in this process are not clear. The most widely accepted mechanism for peptide chain initiation is that proposed several years ago by Staehelin, Anderson, Hersey and coworkers. However, results reported from several laboratories differ significantly from the results on which the above mechanism is based. In this article, we have analyzed these different reports and their significance on the proposed mechanism of peptide chain initiation. Also, we have proposed an alternative mechanism based on the results reported from our laboratory.
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28
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Matts RL, Levin DH, London IM. Fate of reversing factor during restoration of protein synthesis by hemin or GTP in heme-deficient reticulocyte lysates. Proc Natl Acad Sci U S A 1986; 83:1217-21. [PMID: 3456582 PMCID: PMC323046 DOI: 10.1073/pnas.83.5.1217] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The inhibition of protein synthesis in hemedeficient reticulocyte lysates is reversed by the addition of hemin (20 microM) or MgGTP (2 mM). The rate of recovery is rapid and approaches control kinetics within a few minutes after the addition of either component. The restoration of protein synthesis is dependent upon the availability of functional reversing factor (RF). The fate of RF was monitored during recovery by using a method that measures RF activity in the lysate under physiological conditions. In the fully inhibited lysate, RF is sequestered in a nondissociable 15S [RF . eIF-2(alpha P)] complex (where eIF-2 indicates eukaryotic initiation factor 2) in which RF activity is not functional and cannot be assayed. The first step in the rescue of protein synthesis in inhibited lysates by hemin or MgGTP is the inhibition of heme-regulated eIF-2 alpha kinase, which enables endogenous phosphatase to dephosphorylate eIF-2(alpha P) and [RF . eIF-2(alpha P)]. The release of approximately 50% of the sequestered RF activity is sufficient to support optimal kinetics of recovery. Hemin and MgGTP both reverse inhibition by blocking the activation and/or activity of heme-regulated eIF-2 alpha kinase in the lysate. The conclusion that MgGTP exerts its effect on eIF-2 alpha kinase is supported by several in vitro findings: (i) 2 mM MgGTP inhibits the autophosphorylation of purified heme-regulated eIF-2 alpha kinase and abolishes its ability to phosphorylate eIF-2 alpha; (ii) 2 mM MgGTP cannot displace GDP in the binary complexes [eIF-2 . GDP] or [eIF-2(alpha P) . GDP] by mass action; and (iii) RF in the [RF . eIF-2(alpha P)] complex is not dissociated by 2 mM MgGTP.
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29
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Thomas NS, Matts RL, Levin DH, London IM. The 60 S ribosomal subunit as a carrier of eukaryotic initiation factor 2 and the site of reversing factor activity during protein synthesis. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(17)39316-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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30
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The 90-kDa component of reticulocyte heme-regulated eIF-2 alpha (initiation factor 2 alpha-subunit) kinase is derived from the beta subunit of spectrin. Proc Natl Acad Sci U S A 1985; 82:5332-6. [PMID: 2410920 PMCID: PMC390562 DOI: 10.1073/pnas.82.16.5332] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Antibodies from three different lines of monoclonal hybridomas crossreact with both the beta subunit of spectrin and the 90-kDa peptide present in highly purified preparations of the heme-controlled eIF-2 alpha (initiation factor 2 alpha-subunit) kinase from rabbit reticulocytes. Antibodies from two of the three lines enhance the enzymatic activity of the kinase preparation for phosphorylation of the alpha subunit of eukaryotic translational initiation factor 2 (eIF-2) and for phosphorylation of the 100-kDa peptide thought to be a peptide of the kinase that is phosphorylated during its activation. Also, it is shown that both the beta subunit of spectrin and the 90-kDa peptide can be phosphorylated by two protein kinases from reticulocytes, the catalytic subunit of cAMP-dependent protein kinase and a cAMP-independent protein kinase similar to casein kinase II. Furthermore, a phosphorylated 90-kDa peptide can be derived from phosphorylated beta subunit of spectrin by tryptic proteolysis. We conclude that the 90-kDa peptide is derived by proteolysis from the beta subunit of spectrin, probably from its carboxyl terminus, and suggest that the heme-sensitive eIF-2 alpha kinase, like the 56-kDa phosphatase [Wollny, E., Watkins, K., Kramer, G. & Hardesty, B. (1984) J. Biol. Chem. 259, 2484-2492], is associated with an element of the membrane skeleton in intact reticulocytes.
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31
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Gross M, Redman R, Kaplansky DA. Evidence that the primary effect of phosphorylation of eukaryotic initiation factor 2(alpha) in rabbit reticulocyte lysate is inhibition of the release of eukaryotic initiation factor-2.GDP from 60 S ribosomal subunits. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(17)39391-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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32
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Raychaudhuri P, Chaudhuri A, Maitra U. Eukaryotic initiation factor 5 from calf liver is a single polypeptide chain protein of Mr = 62,000. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)89527-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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33
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Raychaudhuri P, Chaudhuri A, Maitra U. Formation and release of eukaryotic initiation factor 2 X GDP complex during eukaryotic ribosomal polypeptide chain initiation complex formation. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)89528-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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34
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Salimans M, Goumans H, Amesz H, Benne R, Voorma HO. Regulation of protein synthesis in eukaryotes. Mode of action of eRF, an eIF-2-recycling factor from rabbit reticulocytes involved in GDP/GTP exchange. EUROPEAN JOURNAL OF BIOCHEMISTRY 1984; 145:91-8. [PMID: 6101245 DOI: 10.1111/j.1432-1033.1984.tb08526.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The rate of initiation of protein synthesis appears to be controlled at the level of recycling of eIF-2. In this process a new factor, designated eRF, plays an important role. The factor has been purified from the post-ribosomal supernatant and has been called formerly anti-HRI and anti-inhibitor [Amesz, H., Goumans, H., Haubrich-Morree, Th., Voorma, H.O., and Benne, R. (1979) Eur. J. Biochem. 98, 513-520]. Its effect on the initiation of protein synthesis has been studied in several assays: a small but distinct effect is found in the assay for the formation of a ternary complex between eIF-2, GTP and Met-tRNA; a 4-5-fold stimulation is obtained in assays for 40S preinitiation complex formation and in the methionyl-puromycin reaction. In the latter assay a catalytic use of eIF-2 occurs provided that eRF is present. eRF forms a complex with eIF-2 which results in a decrease of the affinity of eIF-2 for GDP, giving it the properties of a GDP/GTP exchange factor. The model stresses the catalytic use of eIF-2 in initiation provided that conditions are met for GDP/GTP exchange by a transient complex formation between eIF-2 and eRF. On the other hand, it is shown that phosphorylation of eIF-2 by the hemin-regulated inhibitor (HRI) abolishes the recycling of eIF-2, by the formation of another stable complex comprising eIF-2 alpha P, GDP and eRF.
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35
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Matts RL, London IM. The regulation of initiation of protein synthesis by phosphorylation of eIF-2(alpha) and the role of reversing factor in the recycling of eIF-2. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)39785-5] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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36
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Goss DJ, Parkhurst LJ, Mehta HB, Woodley CL, Wahba AJ. Studies on the role of eukaryotic nucleotide exchange factor in polypeptide chain initiation. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)42798-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Chaney SG, Williams WL, Willingham W, Considine RT, Hall IH, Lee KH. Inhibition of protein synthesis initiation factors by naturally occurring sulfhydryl reactive reagents. CURRENT TOPICS IN CELLULAR REGULATION 1984; 24:251-60. [PMID: 6094109 DOI: 10.1016/b978-0-12-152824-9.50030-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Wahba AJ, Woodley CL. Molecular aspects of development in the brine shrimp Artemia. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1984; 31:221-65. [PMID: 6397772 DOI: 10.1016/s0079-6603(08)60379-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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39
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De Benedetti A, Baglioni C. Phosphorylation of initiation factor eIF-2 alpha, binding of mRNA to 48 S complexes, and its reutilization in initiation of protein synthesis. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(17)43899-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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Abstract
This paper reviews the evidence that protein synthesis in rabbit reticulocytes is regulated by the reversible phosphorylation of the initiation factor eIF-2 by protein kinases under the control of the cytoplasmic haemin concentration on the one hand, and double-stranded RNA on the other. A molecular mechanism is proposed to account for the observation that inhibition of protein synthesis occurs when considerably less than half the eIF-2 present has been phosphorylated. The question of whether phosphorylation regulates protein synthesis in other types of cell is discussed.
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A GDP/GTP exchange factor essential for eukaryotic initiation factor 2 cycling in Ehrlich ascites tumor cells and its regulation by eukaryotic initiation factor 2 phosphorylation. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(20)82007-9] [Citation(s) in RCA: 130] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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42
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Pain VM, Clemens MJ. Assembly and breakdown of mammalian protein synthesis initiation complexes: regulation by guanine nucleotides and by phosphorylation of initiation factor eIF-2. Biochemistry 1983; 22:726-33. [PMID: 6551177 DOI: 10.1021/bi00273a003] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Eukaryotic cell polypeptide chain initiation factor eIF-2 forms ternary complexes with GTP and initiator Met-tRNAf. These complexes can be destabilized in vitro by the addition of salt-washed 40S ribosomal subunits. Our evidence suggests that this destabilization is mediated by GDP generated by premature hydrolysis of the GTP molecule present in the ternary complex. With complexes formed by using a partially purified preparation of eIF-2 from Ehrlich ascites tumor cells, it is possible to reverse the 40S subunit induced inhibition by creating conditions which eliminate free GDP from the system. This reversal probably occurs due to exchange of GTP for the GDP bound to the initiation factor, in a reaction catalyzed by another factor present in the eIF-2 preparation. However, if the eIF-2 has previously been phosphorylated by the reticulocyte heme-controlled repressor, the 40S subunit induced inhibition cannot be reversed by elimination of free GDP. The instability of initiation complexes containing eIF-2, together with the impairment of guanine nucleotide exchange after phosphorylation of eIF-2 [Clemens, M.J., Pain, V.M., Wong, S.-T., & Henshaw, E. C. (1982) Nature (London) 296, 93-95], may be an important aspect of the mechanism of the inhibition of translation by the heme-controlled repressor.
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43
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Matts RL, Levin DH, London IM. Effect of phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 on the function of reversing factor in the initiation of protein synthesis. Proc Natl Acad Sci U S A 1983; 80:2559-63. [PMID: 6573671 PMCID: PMC393865 DOI: 10.1073/pnas.80.9.2559] [Citation(s) in RCA: 111] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The reticulocyte reversing factor (RF) isolated as a complex with eukaryotic initiation factor 2 (eIF-2) acts catalytically in restoring protein synthesis in reticulocyte lysates inhibited by heme deficiency. In reconstituted in vitro assay mixtures containing Mg2+ (0.25-0.5 mM), RF catalyzes the formation of the binary complex (eIF-2-GDP) but this effect is inhibited when eIF-2 is phosphorylated by the heme-regulated kinase for the alpha-subunit of eIF-2 (HRI). More significantly, RF catalyzes the rapid dissociation of (eIF-2-GDP), which permits the exchange of GTP for GDP and, in the presence of Met-tRNAf, promotes the formation of the ternary complex (eIF-2-Met-tRNAf X GTP). However, phosphorylation of the binary complex by HRI prevents its dissociation by RF and, as a consequence, ternary complex formation is inhibited. Our results indicate that phosphorylated binary complex [eIF-2(alpha P).GDP] interacts with RF to form a [RF . eIF-2(alpha P)] that is not readily dissociable. This binding of RF renders it unavailable to catalyze the dissociation of unphosphorylated binary complex, thereby blocking the recycling of eIF-2. Since RF is present in lysates at a limited concentration relative to that of eIF-2, the sequestering of RF in this manner could account for the observation that the phosphorylation of a small proportion of eIF-2 in heme-deficient lysates is sufficient to inhibit protein synthesis.
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Purification of the eukaryotic initiation factor 2-eukaryotic initiation factor 2B complex and characterization of its guanine nucleotide exchange activity during protein synthesis initiation. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)32875-8] [Citation(s) in RCA: 134] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Voorma HO, Goumans H, Amesz H, Benne R. The control of the rate of initiation of eukaryotic protein synthesis. CURRENT TOPICS IN CELLULAR REGULATION 1983; 22:51-70. [PMID: 6347527 DOI: 10.1016/b978-0-12-152822-5.50006-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Nilsen TW, Maroney PA, Baglioni C. Inhibition of protein synthesis in reovirus-infected HeLa cells with elevated levels of interferon-induced protein kinase activity. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)33315-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Proud CG, Clemens MJ, Pain VM. Regulation of binding of initiator tRNA to eukaryotic initiation factor eIF-2. Effects of the haem-controlled repressor on the kinetics of ternary complex formation. FEBS Lett 1982; 148:214-20. [PMID: 6924897 DOI: 10.1016/0014-5793(82)80810-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Ternary complex formation was studied in reticulocyte lysate supernatants and using rat liver eukaryotic initiation factor-2 (eIF-2) preparations. Haem-deficiency reduced the rate of formation of ternary (Met-tRNAf . GTP . eIF-2) complexes by the eIF-2 in reticulocyte supernatants, the reduction being more marked when complex formation was assayed in the absence of GTP-regenerating capacity. Pretreatment with the haem-controlled repressor (HCR) reduced the rate of ternary complex formation by crude (liver) eIF-2. In contrast, complex formation by an almost homogeneous eIF-2 preparation was unaffected by HCR: sensitivity to HCR was however restored by a factor which catalyses exchange of guanine nucleotides bound to eIF-2.
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Inhibition of protein synthesis in vitro by procollagen-derived fragments is associated with changes in protein phosphorylation. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)34155-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Wong ST, Mastropaolo W, Henshaw EC. Differential phosphorylation of soluble versus ribosome-bound eukaryotic initiation factor 2 in the Ehrlich ascites tumor cell. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)34660-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Clemens MJ, Pain VM, Wong ST, Henshaw EC. Phosphorylation inhibits guanine nucleotide exchange on eukaryotic initiation factor 2. Nature 1982; 296:93-5. [PMID: 7063012 DOI: 10.1038/296093a0] [Citation(s) in RCA: 133] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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