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Komar AA, Merrick WC. A Retrospective on eIF2A-and Not the Alpha Subunit of eIF2. Int J Mol Sci 2020; 21:E2054. [PMID: 32192132 PMCID: PMC7139343 DOI: 10.3390/ijms21062054] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Revised: 02/29/2020] [Accepted: 03/13/2020] [Indexed: 12/31/2022] Open
Abstract
Initiation of protein synthesis in eukaryotes is a complex process requiring more than 12 different initiation factors, comprising over 30 polypeptide chains. The functions of many of these factors have been established in great detail; however, the precise role of some of them and their mechanism of action is still not well understood. Eukaryotic initiation factor 2A (eIF2A) is a single chain 65 kDa protein that was initially believed to serve as the functional homologue of prokaryotic IF2, since eIF2A and IF2 catalyze biochemically similar reactions, i.e., they stimulate initiator Met-tRNAi binding to the small ribosomal subunit. However, subsequent identification of a heterotrimeric 126 kDa factor, eIF2 (α,β,γ) showed that this factor, and not eIF2A, was primarily responsible for the binding of Met-tRNAi to 40S subunit in eukaryotes. It was found however, that eIF2A can promote recruitment of Met-tRNAi to 40S/mRNA complexes under conditions of inhibition of eIF2 activity (eIF2α-phosphorylation), or its absence. eIF2A does not function in major steps in the initiation process, but is suggested to act at some minor/alternative initiation events such as re-initiation, internal initiation, or non-AUG initiation, important for translational control of specific mRNAs. This review summarizes our current understanding of the eIF2A structure and function.
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Affiliation(s)
- Anton A. Komar
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological and Environmental Sciences, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA;
| | - William C. Merrick
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA;
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2
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OLA1 regulates protein synthesis and integrated stress response by inhibiting eIF2 ternary complex formation. Sci Rep 2015; 5:13241. [PMID: 26283179 PMCID: PMC4539610 DOI: 10.1038/srep13241] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Accepted: 07/10/2015] [Indexed: 01/06/2023] Open
Abstract
Translation is a fundamental cellular process, and its dysregulation can contribute to human diseases such as cancer. During translation initiation the eukaryotic initiation factor 2 (eIF2) forms a ternary complex (TC) with GTP and the initiator methionyl-tRNA (tRNAi), mediating ribosomal recruitment of tRNAi. Limiting TC availability is a central mechanism for triggering the integrated stress response (ISR), which suppresses global translation in response to various cellular stresses, but induces specific proteins such as ATF4. This study shows that OLA1, a member of the ancient Obg family of GTPases, is an eIF2-regulatory protein that inhibits protein synthesis and promotes ISR by binding eIF2, hydrolyzing GTP, and interfering with TC formation. OLA1 thus represents a novel mechanism of translational control affecting de novo TC formation, different from the traditional model in which phosphorylation of eIF2α blocks the regeneration of TC. Depletion of OLA1 caused a hypoactive ISR and greater survival in stressed cells. In vivo, OLA1-knockdown rendered cancer cells deficient in ISR and the downstream proapoptotic effector, CHOP, promoting tumor growth and metastasis. Our work suggests that OLA1 is a novel translational GTPase and plays a suppressive role in translation and cell survival, as well as cancer growth and progression.
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3
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Sokabe M, Fraser CS. Human eukaryotic initiation factor 2 (eIF2)-GTP-Met-tRNAi ternary complex and eIF3 stabilize the 43 S preinitiation complex. J Biol Chem 2014; 289:31827-31836. [PMID: 25246524 DOI: 10.1074/jbc.m114.602870] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The formation of a stable 43 S preinitiation complex (PIC) must occur to enable successful mRNA recruitment. However, the contributions of eIF1, eIF1A, eIF3, and the eIF2-GTP-Met-tRNAi ternary complex (TC) in stabilizing the 43 S PIC are poorly defined. We have reconstituted the human 43 S PIC and used fluorescence anisotropy to systematically measure the affinity of eIF1, eIF1A, and eIF3j in the presence of different combinations of 43 S PIC components. Our data reveal a complicated network of interactions that result in high affinity binding of all 43 S PIC components with the 40 S subunit. Human eIF1 and eIF1A bind cooperatively to the 40 S subunit, revealing an evolutionarily conserved interaction. Negative cooperativity is observed between the binding of eIF3j and the binding of eIF1, eIF1A, and TC with the 40 S subunit. To overcome this, eIF3 dramatically increases the affinity of eIF1 and eIF3j for the 40 S subunit. Recruitment of TC also increases the affinity of eIF1 for the 40 S subunit, but this interaction has an important indirect role in increasing the affinity of eIF1A for the 40 S subunit. Together, our data provide a more complete thermodynamic framework of the human 43 S PIC and reveal important interactions between its components to maintain its stability.
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Affiliation(s)
- Masaaki Sokabe
- Department of Molecular and Cellular Biology, College of Biological Sciences, University of California, Davis, California 95616
| | - Christopher S Fraser
- Department of Molecular and Cellular Biology, College of Biological Sciences, University of California, Davis, California 95616.
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Sokabe M, Fraser CS, Hershey JWB. The human translation initiation multi-factor complex promotes methionyl-tRNAi binding to the 40S ribosomal subunit. Nucleic Acids Res 2011; 40:905-13. [PMID: 21940399 PMCID: PMC3258154 DOI: 10.1093/nar/gkr772] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The delivery of Met-tRNAi to the 40S ribosomal subunit is thought to occur by way of a ternary complex (TC) comprising eIF2, GTP and Met-tRNAi. We have generated from purified human proteins a stable multifactor complex (MFC) comprising eIF1, eIF2, eIF3 and eIF5, similar to the MFC reported in yeast and plants. A human MFC free of the ribosome also is detected in HeLa cells and rabbit reticulocytes, indicating that it exists in vivo. In vitro, the MFC-GTP binds Met-tRNAi and delivers the tRNA to the ribosome at the same rate as the TC. However, MFC-GDP shows a greatly reduced affinity to Met-tRNAi compared to that for eIF2-GDP, suggesting that MFC components may play a role in the release of eIF2-GDP from the ribosome following AUG recognition. Since an MFC–Met-tRNAi complex is detected in cell lysates, it may be responsible for Met-tRNAi–40S ribosome binding in vivo, possibly together with the TC. However, the MFC protein components also bind individually to 40S ribosomes, creating the possibility that Met-tRNAi might bind directly to such 40S-factor complexes. Thus, three distinct pathways for Met-tRNAi delivery to the 40S ribosomal subunit are identified, but which one predominates in vivo remains to be elucidated.
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Affiliation(s)
- Masaaki Sokabe
- Department of Biochemistry and Molecular Medicine, University of California, Davis, CA 95616, USA
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5
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eIF1 controls multiple steps in start codon recognition during eukaryotic translation initiation. J Mol Biol 2009; 394:268-85. [PMID: 19751744 DOI: 10.1016/j.jmb.2009.09.017] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2009] [Revised: 09/04/2009] [Accepted: 09/09/2009] [Indexed: 11/22/2022]
Abstract
Eukaryotic translation initiation factor (eIF) 1 is a central mediator of start codon recognition. Dissociation of eIF1 from the preinitiation complex (PIC) allows release of phosphate from the G-protein factor eIF2, triggering downstream events in initiation. Mutations that weaken binding of eIF1 to the PIC decrease the fidelity of start codon recognition (Sui(-) phenotype) by allowing increased eIF1 release at non-AUG codons. Consistent with this, overexpression of these mutant proteins suppresses their Sui(-) phenotypes. Here, we have examined mutations at the penultimate residue of eIF1, G107, that produce Sui(-) phenotypes without increasing the rate of eIF1 release. We provide evidence that, in addition to its role in gating phosphate release, dissociation of eIF1 triggers conversion from an open, scanning-competent state of the PIC to a stable, closed one. We also show that eIF5 antagonizes binding of eIF1 to the complex and that key interactions of eIF1 with its partners are modulated by the charge at and around G107. Our data indicate that eIF1 plays multiple roles in start codon recognition and suggest that prior to AUG recognition it prevents eIF5 from binding to a key site in the PIC required for triggering downstream events.
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6
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Robert F, Kapp LD, Khan SN, Acker MG, Kolitz S, Kazemi S, Kaufman RJ, Merrick WC, Koromilas AE, Lorsch JR, Pelletier J. Initiation of protein synthesis by hepatitis C virus is refractory to reduced eIF2.GTP.Met-tRNA(i)(Met) ternary complex availability. Mol Biol Cell 2006; 17:4632-44. [PMID: 16928960 PMCID: PMC1635388 DOI: 10.1091/mbc.e06-06-0478] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
A cornerstone of the antiviral interferon response is phosphorylation of eukaryotic initiation factor (eIF)2alpha. This limits the availability of eIF2.GTP.Met-tRNA(i)(Met) ternary complexes, reduces formation of 43S preinitiation complexes, and blocks viral (and most cellular) mRNA translation. However, many viruses have developed counterstrategies that circumvent this cellular response. Herein, we characterize a novel class of translation initiation inhibitors that block ternary complex formation and prevent the assembly of 43S preinitiation complexes. We find that translation driven by the HCV IRES is refractory to inhibition by these compounds at concentrations that effectively block cap-dependent translation in vitro and in vivo. Analysis of initiation complexes formed on the HCV IRES in the presence of inhibitor indicates that eIF2alpha and Met-tRNA(i)(Met) are present, defining a tactic used by HCV to evade part of the antiviral interferon response.
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Affiliation(s)
| | - Lee D. Kapp
- Department of Biophysics and Biophysical Chemistry, John Hopkins University School of Medicine, Baltimore, MD 21205-2185
| | | | - Michael G. Acker
- Department of Biophysics and Biophysical Chemistry, John Hopkins University School of Medicine, Baltimore, MD 21205-2185
| | - Sarah Kolitz
- Department of Biophysics and Biophysical Chemistry, John Hopkins University School of Medicine, Baltimore, MD 21205-2185
| | - Shirin Kazemi
- Lady Davis Institute for Medical Research, McGill University, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada H3T 1E2
| | - Randal J. Kaufman
- Howard Hughes Medical Institute and
- Departments of Biological Chemistry and Internal Medicine, University of Michigan, Ann Arbor, MI 48109; and
| | - William C. Merrick
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4935
| | - Antonis E. Koromilas
- Lady Davis Institute for Medical Research, McGill University, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada H3T 1E2
| | - Jon R. Lorsch
- Department of Biophysics and Biophysical Chemistry, John Hopkins University School of Medicine, Baltimore, MD 21205-2185
| | - Jerry Pelletier
- *Department of Biochemistry and
- McGill Cancer Center, McGill University, Montreal, Quebec, Canada H3G 1Y6
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7
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Kapp LD, Lorsch JR. GTP-dependent recognition of the methionine moiety on initiator tRNA by translation factor eIF2. J Mol Biol 2004; 335:923-36. [PMID: 14698289 DOI: 10.1016/j.jmb.2003.11.025] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Eukaryotic translation initiation factor 2 (eIF2) is a G-protein that functions as a central switch in the initiation of protein synthesis. In its GTP-bound state it delivers the methionyl initiator tRNA (Met-tRNA(i)) to the small ribosomal subunit and releases it upon GTP hydrolysis following the recognition of the initiation codon. We have developed a complete thermodynamic framework for the assembly of the Saccharomyces cerevisiae eIF2.GTP.Met-tRNA(i) ternary complex and have determined the effect of the conversion of GTP to GDP on eIF2's affinity for Met-tRNA(i) in solution. In its GTP-bound state the factor forms a positive interaction with the methionine moiety on Met-tRNA(i) that is disrupted when GTP is replaced with GDP, while contacts between the factor and the body of the tRNA remain intact. This positive interaction with the methionine residue on the tRNA may serve to ensure that only charged initiator tRNA enters the initiation pathway. The toggling on and off of the factor's interaction with the methionine residue is likely to play an important role in the mechanism of initiator tRNA release upon initiation codon recognition. In addition, we show that the conserved base-pair A1:U72, which is known to be a critical identity element distinguishing initiator from elongator methionyl tRNA, is required for recognition of the methionine moiety by eIF2. Our data suggest that a role of this base-pair is to orient the methionine moiety on the initiator tRNA in its recognition pocket on eIF2.
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Affiliation(s)
- Lee D Kapp
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, 725 N. Wolfe Street 625 WBSB, Baltimore, MD 21205-2185, USA
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8
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Role of various carotenoids in mediating electron transfer sensitized by chlorophyll and pheophytin. FEBS Lett 2002. [DOI: 10.1016/0014-5793(82)80269-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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9
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Pelaez F, de Haro C. Translational inhibition by eIF-2-phospholipid complex in mammalian cell-free systems. FEBS Lett 1989; 250:523-8. [PMID: 2753146 DOI: 10.1016/0014-5793(89)80789-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The polypeptide chain initiation factor 2 (eIF-2) binds phospholipid (PL) and becomes a potent inhibitor of translation in hemin-supplemented reticulocyte lysates [De Haro et al. (1986) Proc. Natl. Acad. Sci. USA 83, 6711-6715]. This binding is independent of calcium ions and seems to be specific for phosphatidylinositol or phosphatidylserine; phosphatidic and arachidonic acids are inactive. Like alpha-subunit-phosphorylated eIF-2, eIF-2.PL traps GEF in a non-dissociable eIF-2.PL.GEF complex whereby GEF is no longer able to recycle. Initiation is inhibited when no free GEF is available. Translational inhibition by eIF-2.PL is rescued by equimolar amounts of eIF-2.GEF. On the basis of this stoichiometry, we have estimated that reticulocyte lysates contain about 60 pmol of GEF/ml (60 nM). eIF-2.PL also inhibits translation in cell-free mouse liver extracts and this inhibition is prevented by reticulocyte eIF-2.GEF suggesting that GEF also functions in liver. However, the eIF-2.PL complex does not affect translation in such non-mammalian eukaryotic systems as wheat germ and Drosophila embryos.
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Affiliation(s)
- F Pelaez
- Centro de Biologia Molecular, Consejo Superior de Investigaciones Cientificas, Madrid, Spain
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10
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Roy AL, Chakrabarti D, Datta B, Hileman RE, Gupta NK. Natural mRNA is required for directing Met-tRNA(f) binding to 40S ribosomal subunits in animal cells: involvement of Co-eIF-2A in natural mRNA-directed initiation complex formation. Biochemistry 1988; 27:8203-9. [PMID: 3233204 DOI: 10.1021/bi00421a033] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Two protein factors, eIF-2 as well as a high molecular weight protein complex from reticulocyte ribosomal high-salt wash which we term Co-eIF-2, promote Met-tRNA(f) binding to 40S ribosomes. This binding is dependent on the presence of an AUG codon or natural mRNAs [Roy et al. (1984) Biochem. Biophys. Res. Commun. 122, 1418-1425]. Co-eIF-2 contains two component activities, Co-eIF-2A and Co-eIF-2C. Previously, we have purified an 80-kDa polypeptide containing Co-eIF-2A activity and showed that this polypeptide is a component of Co-eIF-2 and is responsible for Co-eIF-2A activity in Co-eIF-2 [Chakravarty et al. (1985) J. Biol. Chem. 260, 6945-6949]. We now report purification of a protein complex (subunits of Mr 180K, 110K, 65K, 63K, 53K, 50K, 43K, and 40K) containing Co-eIF-2C activity and devoid of Co-eIF-2A activity. In SDS-PAGE, the purified Co-eIF-2C preparation and an eIF-3 preparation (purified in Dr. A. Wahba's laboratory) separated into seven similar major polypeptides (Mr 110K, 65K, 63K, 53K, 50K, 43K, and 40K). The 50-kDa polypeptide in Co-eIF-2C was immunoreactive with a monoclonal antibody against eIF-4A (50 kDa). We have studied the roles of purified Co-eIF-2A and Co-eIF-2C activities in ternary and Met-tRNA(f).40S ribosome complex formation. The results are as follows: (1) At low and presumably physiological factor concentration (30 nM), eIF-2 did not form detectable levels of ternary complex. Moreover, such complex formation was totally dependent on the presence of Co-eIF-2A and/or Co-eIF-2C.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- A L Roy
- Department of Chemistry, University of Nebraska, Lincoln 68588-0304
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11
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Cigan AM, Feng L, Donahue TF. tRNAi(met) functions in directing the scanning ribosome to the start site of translation. Science 1988; 242:93-7. [PMID: 3051379 DOI: 10.1126/science.3051379] [Citation(s) in RCA: 158] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The mechanism by which the scanning ribosome recognizes the first AUG codon nearest the 5' end of eukaryotic messenger RNA has not been established. To investigate this an anticodon change (3'-UCC-5') was introduced into one of the four methionine initiator (tRNAi(met) genes of Saccharomyces cerevisiae. The ability of the mutant transfer RNA to restore growth properties to his4 initiator codon mutant yeast strains in the absence of histidine was then assayed. Only the complementary codon, AGG, at the his4 initiator region supported His+ growth. The mutant transfer RNA also directed the ribosome to initiate at an AGG placed in the upstream region of the his4 message. Initiation at this upstream AGG precluded initiation at a downstream AGG in accordance with the "scanning" model. Therefore, an anticodon: codon interaction between tRNAi(met) as part of the scanning ribosome and the first AUG must function in directing the ribosome to the eukaryotic initiator region.
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Affiliation(s)
- A M Cigan
- Department of Molecular Biology, Northwestern University Medical School, Chicago, IL 60611
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12
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Panniers R, Rowlands AG, Henshaw EC. The effect of Mg2+ and guanine nucleotide exchange factor on the binding of guanine nucleotides to eukaryotic initiation factor 2. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)60595-2] [Citation(s) in RCA: 23] [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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13
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Rubin HN, Almendarez E, Halim MN. Do pyrimidine nucleotides regulate translatability of globin mRNA as purine nucleotides do? THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1988; 20:1051-9. [PMID: 3248665 DOI: 10.1016/0020-711x(88)90249-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
1. When rabbit globin mRNA was incubated with rabbit reticulocyte lysate in the presence of various concentrations of nucleotides, globin synthesis was inhibited or stimulated dependent on dose. 2. Pyrimidine nucleotides inhibited protein synthesis at 0.3 mM, whereas 2 mM of purine nucleotides were required to cause similar inhibition. 3. Adenosine mono- and diphosphate inhibited globin synthesis at a concentration of only 1 mM; however, the sequence is AMP greater than ADP greater than ATP. 4. Translation arrest by these nucleotides was instantaneous. 5. These results suggest that these nucleotides may provide a structural component for maintaining the integrity, the conformation of mRNA or of the messenger ribonucleoprotein (mRNP).
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14
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Roy AL, Chakrabarti D, Gupta NK. Protein synthesis in rabbit reticulocytes: Mg2+-inhibition of ternary complex (Met-tRNA(f).eIF-2.GTP) formation by reticulocyte eIF-2. Biochem Biophys Res Commun 1987; 146:114-20. [PMID: 3649231 DOI: 10.1016/0006-291x(87)90698-x] [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: 01/06/2023]
Abstract
There are conflicting reports regarding Mg2+-inhibition of ternary complex formation by reticulocyte eIF-2. Several laboratories have reported that eIF-2 is isolated as eIF-2.GDP and Mg2+ inhibits ternary complex formation, as in the presence of Mg2+, GDP remains tightly bound to eIF-2 and prevents ternary complex formation. A protein factor, GEF is necessary for GDP displacement and subsequent ternary complex formation. Other laboratories have reported that Mg2+ has no effect on eIF-2 activity and eIF-2 forms near stoichiometric amount of ternary complex in the presence of Mg2+. In this paper, we provide evidence which suggests that the Mg2+-insensitive eIF-2 activity as reported by several laboratories might have been the result of the use of high Met-tRNA(f) concentrations in their assays as the nucleotides in excess tRNA bound Mg2+ in the reaction mixture and there was no free Mg2+ available to inhibit eIF-2 activity. Our data will show that the addition of excess tRNA promotes non-enzymatic GDP displacement from eIF-2.GDP and relieves Mg2+ inhibition.
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17
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Thoen C, Van Hove L, Slegers H. Identification of the substrates of the casein kinase II associated with non-polysomal messenger ribonucleoproteins of A. salina cryptobiotic embryos. Mol Biol Rep 1986; 11:69-75. [PMID: 3461261 DOI: 10.1007/bf00364816] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The association of a protein kinase with cytoplasmic non-polysomal messenger ribonucleoproteins is demonstrated by chromatography on oligo(dT)-cellulose and sucrose gradient centrifugation. The cAMP-independent enzyme is inhibited by caffeine and poly(L)-glutamic acid and is classified as a casein kinase II. Among the exogenous proteins initiation factor eIF2 is the best substrate and is 7.8 times more efficiently phosphorylated than casein. Endogenous mRNP protein substrates have a Mr of 125 000, 65 000, 38 000, 26 000 and 23 500. The main phosphate acceptor is the Mr 38 000 poly(A)-binding protein. Dephosphorylation of the poly(A)-binding protein by protein phosphatases decreases its RNA binding property. The effect of phosphorylation-dephosphorylation of mRNP proteins on the initiation of protein synthesis is discussed.
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18
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Austin SA, Pollard JW, Jagus R, Clemens MJ. Regulation of polypeptide chain initiation and activity of initiation factor eIF-2 in Chinese-hamster-ovary cell mutants containing temperature-sensitive aminoacyl-tRNA synthetases. EUROPEAN JOURNAL OF BIOCHEMISTRY 1986; 157:39-47. [PMID: 3519214 DOI: 10.1111/j.1432-1033.1986.tb09635.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The regulation of polypeptide chain initiation has been investigated in extracts from a number of well-characterized Chinese hamster ovary (CHO) cell mutants containing different temperature-sensitive aminoacyl-tRNA synthetases. These cells exhibit a large decline in the rate of initiation when cultures are shifted from the permissive temperature of 34 degrees C to the non-permissive temperature of 39.5 degrees C. During a brief incubation with [35S]Met-tRNAMetf or [35S]methionine, formation of initiation complexes on native 40S ribosomal subunits and 80S ribosomes is severely impaired in extracts from the mutant cell lines exposed to 39.5 degrees C. Wild-type cells exposed to 39.5 degrees C do not show any inhibition of protein synthesis or initiation complex formation. Inhibition of formation of 40S initiation complexes in the extracts from mutant cells, incubated at the non-permissive temperature, is shown to be independent of possible changes in mRNA binding or the rate of polypeptide chain elongation and is not due to any decrease in the total amount of initiation factor eIF-2 present. However, assays of eIF-2 X GTP X Met-tRNAMetf ternary complex formation in postribosomal supernatants from the temperature-sensitive mutants reveal a marked defect in the activity of eIF-2 after exposure of the cells to 39.5 degrees C and addition of exogenous eIF-2 to cell-free protein-synthesizing systems from cells incubated at 34 degrees C and 39.5 degrees C eliminates the difference in activity between them. The activity of the initiation factor itself is not directly temperature-sensitive in the mutant CHO cells. The results suggest that the activity of aminoacyl-tRNA synthetases can affect the ability of eIF-2 to bind Met-tRNAMetf and form 40S initiation complexes in intact cells, indicating a regulatory link between polypeptide chain elongation and chain initiation.
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19
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Abstract
We have isolated three distinct tRNAimet genes from a yeast DNA clone bank. The complete sequence of two shows that these genes are colinear with the mature tRNAimet and supports the RNA sequence of tRNAimet. Southern analysis of yeast genomic DNA indicates the presence of four copies of tRNAimet gene per haploid genome.
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20
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de Herdt E, Piot E, Wahba A, Slegers H. Initiation factor eIF2 associated with non-polysomal poly(A)-containing messenger ribonucleoproteins of cryptobiotic gastrulae of Artemia salina. EUROPEAN JOURNAL OF BIOCHEMISTRY 1985; 151:455-60. [PMID: 2863143 DOI: 10.1111/j.1432-1033.1985.tb09123.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Non-polysomal poly(A)-containing mRNP of A. salina cryptobiotic embryos is separated in mRNP active in protein synthesis and in repressed mRNP by sucrose gradient centrifugation. In the translationally active fraction the presence of eukaryotic initiation factor 2 (eIF2) is demonstrated by electroblotting of sodium dodecylsulphate/polyacrylamide gels on nitrocellulose and anti-eIF2 antibody detection. mRNP proteins with Mr of 40 000 and 42 000 are identified as the alpha and beta subunits of eIF2. The repressed mRNP is devoid of eIF2 and is associated with an inhibitor ribonucleoprotein composed of a small 85 +/- 2-nucleotide-long RNA and a protein with Mr of 64 000. The latter ribonucleoprotein is a potent inhibitor of the translationally active mRNP.
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Ribosome-associated cyclic nucleotide-independent protein kinase of Artemia salina cryptobiotic gastrulae. BIOCHIMICA ET BIOPHYSICA ACTA 1985; 825:268-79. [PMID: 2990557 DOI: 10.1016/0167-4781(85)90014-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
An extra-ribosomal cAMP-independent protein kinase from cryptobiotic embryos of Artemia salina has been purified to near homogeneity by gel filtration on Bio-Gel A-0.5 m, ion-exchange chromatography on DEAE-cellulose and phosphocellulose P11 and affinity chromatography on casein-Sepharose 4B and ATP-agarose. The enzymatic activity has a broad optimum at pH 7-8. Maximal activity is obtained in the presence of 5-6 mM MgCl2. The activity is inhibited by Mn2+, Ca2+ and K+. The enzyme has an Mr of 127 000, utilizes both ATP and GTP as phosphoryl donors and is completely inhibited by heparin and poly(L-glutamic acid). According to its properties, the enzyme can be classified as a casein kinase type II. Although the enzyme is associated with ribosomes, ribosomal proteins are not among the main substrates. The kinase is able to phosphorylate both the alpha and the beta subunits of initiation factor eIF2 using ATP or GTP as phosphoryl donors. The function of phosphorylation in the initiation of protein synthesis is discussed.
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Setyono B, Van Steeg H, Voorma HO. Ultraviolet-crosslinking reveals specific affinity of eukaryotic initiation factors for Semliki Forest virus mRNA. BIOCHIMICA ET BIOPHYSICA ACTA 1984; 782:242-6. [PMID: 6733107 DOI: 10.1016/0167-4781(84)90058-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Eukaryotic initiation factors (eIF) associate readily with 32P-labeled Semliki Forest virus (SFV) mRNA in vitro, forming complexes which can be crosslinked by 254 nm ultraviolet irradiation. After ribonuclease digestion, the initiation factors were released and analysed by gel electrophoresis. Autoradiography revealed proteins by virtue of crosslinked 32P-labeled mRNA fragments. eIF-4A, -4B and -4C as well as three subunits of eIF-3 could be crosslinked with SFV mRNA. None of these proteins bound to ribosomal RNAs.
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Wagner T, Gross M, Sigler PB. Isoleucyl initiator tRNA does not initiate eucaryotic protein synthesis. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)42903-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Osterhout JJ, Lax SR, Ravel JM. Factors from wheat germ that enhance the activity of eukaryotic initiation factor eIF-2. Isolation and characterization of Co-eIF-2 alpha. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(20)82062-6] [Citation(s) in RCA: 18] [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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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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Factors from wheat germ that enhance the activity of eukaryotic initiation factor eIF-2. Isolation and characterization of Co-eIF-2 beta. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)34322-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] 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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Jagus R, Crouch D, Konieczny A, Safer B. The role of phosphorylation in the regulation of eukaryotic initiation factor 2 activity. CURRENT TOPICS IN CELLULAR REGULATION 1982; 21:35-63. [PMID: 6291856 DOI: 10.1016/b978-0-12-152821-8.50006-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Abstract
The regulation of eIF-2 activity during protein synthesis initiation has been postulated to involve phosphorylation/dephosphorylation mechanisms and/or the participation of ancillary protein factors. Both mechanisms would affect directly the binding of initiator methionyl-tRNAi by eIF-2. Recent data concerning the phosphorylation state of eIF-2 in hemin-deficient lysates and other covalent modifications which alter the efficiency of eIF-2 utilization, however, suggest that modulation of eIF-2 activity is more complex, and involves alteration of its catalytic recycling.
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Jagus R, Anderson WF, Safer B. The regulation of initiation of mammalian protein synthesis. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1981; 25:127-85. [PMID: 6164076 DOI: 10.1016/s0079-6603(08)60484-5] [Citation(s) in RCA: 228] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Jakubowicz T, Svoboda AJ, Vaughan MH. Purification and phosphorylation of human initiation factor eIF-2. Biochem Biophys Res Commun 1980; 97:1420-8. [PMID: 7213368 DOI: 10.1016/s0006-291x(80)80024-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Benne R, Salimans M, Goumans H, Amesz H, Voorma HO. Regulation of protein synthesis in rabbit reticulocyte lysates. Phosphorylation of eIF-2 does not inhibit its capacity to recycle. EUROPEAN JOURNAL OF BIOCHEMISTRY 1980; 104:501-9. [PMID: 7363902 DOI: 10.1111/j.1432-1033.1980.tb04452.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Benne R, Kasperaitis M, Voorma HO, Ceglarz E, Legocki AB. Initiation factor eIF-2 from wheat germ. Purification, functional comparison to eIF-2 from rabbit reticulocytes and phosphorylation of its subunits. EUROPEAN JOURNAL OF BIOCHEMISTRY 1980; 104:109-17. [PMID: 7371632 DOI: 10.1111/j.1432-1033.1980.tb04406.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Clemens MJ, Echetebu CO, Tilleray VJ, Pain VM. Stimulation of initiation factor eIF-2 by a rat liver protein with GDPase activity. Biochem Biophys Res Commun 1980; 92:60-7. [PMID: 6101948 DOI: 10.1016/0006-291x(80)91519-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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38
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Amesz H, Goumans H, Haubrich-Morree T, Voorma HO, Benne R. Purification and characterization of a protein factor that reverses the inhibition of protein synthesis by the heme-regulated translational inhibitor in rabbit reticulocyte lysates. EUROPEAN JOURNAL OF BIOCHEMISTRY 1979; 98:513-20. [PMID: 488111 DOI: 10.1111/j.1432-1033.1979.tb13212.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
We have purified and partially characterized a supernatant factor which reverses the effect of the heme-regulated translational inhibitor on protein synthesis in rabbit reticulocyte lysates. The anti-inhibitor restores protein synthesis activity in heme deficient lysates (and in lysates to which the inhibitor has been added) to the level observed in the presence of heme. The factor has no effect on the phosphorylation of eIF-2 by the inhibitor nor on any reaction carried out with purified initiation factors. The anti-inhibitor probably consists of three subunits with molecular weights of 81000, 60000 and 41000. The factor is isolated from the postribosomal supernatant of rabbit reticulocytes both free and complexed to eIF-2. A possible mechanism of action is discussed.
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