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Kim S, Ramalho TR, Haynes CM. Regulation of proteostasis and innate immunity via mitochondria-nuclear communication. J Cell Biol 2024; 223:e202310005. [PMID: 38335010 PMCID: PMC10857905 DOI: 10.1083/jcb.202310005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Revised: 01/29/2024] [Accepted: 01/30/2024] [Indexed: 02/10/2024] Open
Abstract
Mitochondria are perhaps best known as the "powerhouse of the cell" for their role in ATP production required for numerous cellular activities. Mitochondria have emerged as an important signaling organelle. Here, we first focus on signaling pathways mediated by mitochondria-nuclear communication that promote protein homeostasis (proteostasis). We examine the mitochondrial unfolded protein response (UPRmt) in C. elegans, which is regulated by a transcription factor harboring both a mitochondrial- and nuclear-targeting sequence, the integrated stress response in mammals, as well as the regulation of chromatin by mitochondrial metabolites. In the second section, we explore the role of mitochondria-to-nuclear communication in the regulation of innate immunity and inflammation. Perhaps related to their prokaryotic origin, mitochondria harbor molecules also found in viruses and bacteria. If these molecules accumulate in the cytosol, they elicit the same innate immune responses as viral or bacterial infection.
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Affiliation(s)
- Sookyung Kim
- Department of Molecular, Cell and Cancer Biology, University of Massachusetts Chan Medical School, Worcester, MA, USA
| | - Theresa R. Ramalho
- Department of Molecular, Cell and Cancer Biology, University of Massachusetts Chan Medical School, Worcester, MA, USA
| | - Cole M. Haynes
- Department of Molecular, Cell and Cancer Biology, University of Massachusetts Chan Medical School, Worcester, MA, USA
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2
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Squatrito M, Mancino M, Sala L, Draetta GF. Ebp1 is a dsRNA-binding protein associated with ribosomes that modulates eIF2alpha phosphorylation. Biochem Biophys Res Commun 2006; 344:859-68. [PMID: 16631606 DOI: 10.1016/j.bbrc.2006.03.205] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2006] [Accepted: 03/25/2006] [Indexed: 10/24/2022]
Abstract
dsRNA-binding domains (dsRBDs) characterize an expanding family of proteins involved in different cellular processes, ranging from RNA editing and processing to translational control. Here we present evidence that Ebp1, a cell growth regulating protein that is part of ribonucleoprotein (RNP) complexes, contains a dsRBD and that this domain mediates its interaction with dsRNA. Deletion of Ebp1's dsRBD impairs its localization to the nucleolus and its ability to form RNP complexes. We show that in the cytoplasm, Ebp1 is associated with mature ribosomes and that it is able to inhibit the phosphorylation of serine 51 in the eukaryotic initiation factor 2 alpha (eIF2alpha). In response to various cellular stress, eIF2alpha is phosphorylated by distinct protein kinases (PKR, PERK, GCN2, and HRI), and this event results in protein translation shut-down. Ebp1 overexpression in HeLa cells is able to protect eIF2alpha from phosphorylation at steady state and also in response to various treatments. We demonstrate that Ebp1 interacts with and is phosphorylated by the PKR protein kinase. Our results demonstrate that Ebp1 is a new dsRNA-binding protein that acts as a cellular inhibitor of eIF2alpha phosphorylation suggesting that it could be involved in protein translation control.
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Affiliation(s)
- Massimo Squatrito
- European Institute of Oncology, 435 Via Ripamonti, 20141 Milan, Italy.
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BONANOU-TZEDAKI SA, SOHI MK, ARNSTEIN HRV. Regulation of Protein Synthesis in Reticulocyte Lysates. ACTA ACUST UNITED AC 2005. [DOI: 10.1111/j.1432-1033.1981.tb06174.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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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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5
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Affiliation(s)
- C G Proud
- Department of Biochemistry, School of Medical Sciences, University of Bristol, England
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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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7
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Abstract
The initiation factor eIF-2 that specifically binds Met-tRNAf and GTP in ternary complex (eIF-2. GTP. Met-tRNAf) has been purified to apparent homogeneity from wheat germ ribosomal salt wash. The purified factor exhibits a sedimentation coefficient of 5 X 5S and an aggregate molecular weight of 122,000-daltons for the native protein.
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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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9
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Roberts RC, Ranu RS. Regulation of protein synthesis in rabbit reticulocyte lysates. Requirement of initiation factor eIF-2 holoprotein for substrate specificity of heme-regulated protein kinase. FEBS Lett 1986; 209:162-4. [PMID: 3792542 DOI: 10.1016/0014-5793(86)81103-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The specificity of the heme-regulated protein kinase (HRI) was investigated further by utilizing the isolated 38,000 Da subunit (alpha subunit) polypeptide of eIF-2 as the substrate. For this purpose, the three subunit polypeptides of eIF-2 (38,000 Da, alpha; 50,000 Da, beta; and 52,000 Da, gamma) were resolved by reversed-phase high performance liquid chromatography (HPLC). Results show that HRI is incapable of phosphorylating the 38,000 Da subunit separated from the other two eIF-2 polypeptides. Data suggest that the substrate specificity of HRI is determined by the quaternary structure assumed by the alpha subunit in association with the other two subunits in the eIF-2 holoprotein.
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Mehta HB, Dholakia JN, Roth WW, Parekh BS, Montelaro RC, Woodley CL, Wahba AJ. Structural studies on the eukaryotic chain initiation factor 2 from rabbit reticulocytes and brine shrimp Artemia embryos. Phosphorylation by the heme-controlled repressor and casein kinase II. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(19)62673-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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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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Bagchi MK, Chakravarty I, Datta B, Chakrabarti D, Gupta NK. Protein synthesis in rabbit reticulocytes. A study of the mechanism of Co-eIF-2 action. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)95689-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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14
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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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Chakravarty I, Bagchi MK, Roy R, Banerjee AC, Gupta NK. Protein synthesis in rabbit reticulocytes. Purification and properties of an Mr 80,000 polypeptide (Co-eIF-2A80) with Co-eIF-2A activity. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)88871-8] [Citation(s) in RCA: 12] [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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16
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A comparative study of the characteristics of eIF-2 and eIF-2-ancillary factor activities from yeast Saccharomyces cerevisiae and rabbit reticulocytes. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)88874-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Grace M, Bagchi M, Ahmad F, Yeager T, Olson C, Chakravarty I, Nasrin N, Banerjee A, Gupta NK. Protein synthesis in rabbit reticulocytes: a study of the mechanism of action of the protein factor RF that reverses protein synthesis inhibition in heme-deficient reticulocyte lysates. Proc Natl Acad Sci U S A 1984; 81:5379-83. [PMID: 6591195 PMCID: PMC391707 DOI: 10.1073/pnas.81.17.5379] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
A eukaryotic initiation factor 2 (eIF-2)-ancillary protein factor Co-eIF-2 promotes displacement of GDP from eIF-2 X GDP and facilitates ternary complex (Met-tRNAf X eIF-2 X GTP) formation in the presence of Mg2+. Heme-regulated protein synthesis inhibitor, HRI, phosphorylates the alpha-subunit of eIF-2 and thus inhibits ternary complex formation as Co-eIF-2 does not displace GDP from eIF-2 alpha (P) X GDP. RF, a high molecular weight cell supernatant factor, reverses protein synthesis inhibition in heme-deficient reticulocyte lysates and also reverses HRI inhibition of ternary complex formation. RF contains Co-eIF-2 activity. In addition, an active RF preparation contains excess alpha-subunit of eIF-2 in the free and unphosphorylated form and this alpha-subunit of eIF-2 is not phosphorylated by HRI and ATP. In this paper we report (i) an active RF preparation contains excess alpha-subunit of eIF-2 and this alpha-subunit can be phosphorylated by HRI and ATP in the presence of GDP; (ii) RF promotes ternary complex formation by eIF-2 X [3H]GDP with accompanying GDP displacement; (iii) in the presence of HRI and ATP, RF promotes ternary complex formation by eIF-2 X [3H]GDP without accompanying GDP displacement; (iv) in the presence of HRI and ATP, the ternary complex formed using RF is active in Met-tRNAf X 40S initiation complex formation; (v) both the ternary complex and the Met-tRNAf X 40S complex formation in the presence of HRI and ATP are completely inhibited by prior incubation of RF with GDP; (vi) upon further fractionation of an active RF fraction, a preparation can be obtained that contains HRI-sensitive Co-eIF-2 activity. However, this preparation does not efficiently reverse protein synthesis inhibition in heme-deficient reticulocyte lysates and does not contain excess alpha-subunit of eIF-2. Based on these observations, we have suggested (a) RF provides the unphosphorylated alpha-subunit to eIF-2 alpha (P) X GDP and restores eIF-2 activity. This RF activity is inhibited as the alpha-subunit in the RF preparation becomes phosphorylated by HRI and ATP in the presence of GDP; (b) RF contains Co-eIF-2 activity, which has dual functions: (i) stimulation of ternary complex formation by eIF-2 and (ii) GDP displacement from eIF-2 X GDP during ternary complex formation. In the presence of HRI and ATP, Co-eIF-2 but does not displace GDP from eIF-2 alpha(P) X GDP.
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18
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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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20
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Sarkar S. Translational control involving a novel cytoplasmic RNA and ribonucleoprotein. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1984; 31:267-93. [PMID: 6085172 DOI: 10.1016/s0079-6603(08)60380-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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21
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Wheat germ eIF2 and CoeIF2. Resolution and functional characterization in in vitro protein synthesis. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(17)44494-2] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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22
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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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23
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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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Abstract
Vanadate inhibits protein chain initiation in rabbit reticulocyte lysates. The evidence that supports this conclusion is as follows: (i) the biphasic kinetics of inhibition in which protein synthesis is maintained at the control rate for 1-2 min is followed by an abrupt decline in the rate of synthesis; (ii) inhibition is associated with a marked disaggregation of polyribosomes and a concomitant increase in 80S ribosomes; and (iii) vanadate concentrations that inhibit protein chain initiation do not inhibit polypeptide chain elongation or the aminoacylation of tRNA. In partial reactions of protein chain initiation, vanadate concentrations that inhibit protein synthesis have no detectable effect on the formation of eukaryotic initiation factor eIF-2-promoted ternary complex with Met-tRNAf and GTP and on the assembly of 40S ribosomal subunit-Met-tRNAf complexes. On the addition of mRNA, the 40S ribosomal subunit-Met-tRNAf complexes also are transformed into 80S ribosome-mRNA-Met-tRNAf complexes, termed 80S initiation complexes. In vanadate-treated samples, however, these 80S initiation complexes are defective and unable to proceed beyond this step.
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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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Siekierka J, Manne V, Mauser L, Ochoa S. Polypeptide chain initiation in eukaryotes: reversibility of the ternary complex-forming reaction. Proc Natl Acad Sci U S A 1983; 80:1232-5. [PMID: 6572381 PMCID: PMC393569 DOI: 10.1073/pnas.80.5.1232] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
In the last step of polypeptide chain initiation in eukaryotes, the interaction of the 40S preinitiation complex eIF-2.GTP.Met-tRNAi.40S [the complex between the 40S ribosomal subunit and the ternary complex containing equimolar amounts of eukaryotic initiation factor 2 (eIF-2), GTP, and eukaryotic initiator methionyl tRNA (Met-tRNAi)] with a 60S ribosomal subunit in the presence of mRNA, cap binding protein (with "capped" messengers), ATP, and the initiation factors eIF-3, eIF-4a, -4b, -4c, and eIF-5, results in the formation of an 80S initiation complex (Met-tRNAi.80S.mRNA) with concomitant hydrolysis of GTP and liberation of eIF-2 for recycling in subsequent initiation events. However, at physiological Mg2+ concentrations, GDP is known to have approximately equal to 100-fold greater affinity than GTP for eIF-2 and eIF-2 is believed to be released in the form of an eIF-2.GDP complex. Previously, we have shown that initiation factor SP (for eIF-2-stimulating protein) promotes the exchange of eIF-2-bound GDP for GTP and catalyzes ternary complex formation in the presence of Met-tRNAi. Binding of GDP by eIF-2 is indeed so tight that, as we now show, homogeneous preparations of eIF-2 contain upward of 0.5 mol of GDP/mol of eIF-2. We further show that, in the presence of Mg2+ and catalytic amounts of SP, ternary complex formation conforms to the overall reversible reaction eIF-2.GDP + GTP + Met-tRNAi in equilibrium eIF-2.GTP.Met-tRNAi + GDP.
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Protein synthesis in brine shrimp embryos and rabbit reticulocytes. The effect of Mg2+ on binary (eukaryotic initiation factor 2 X GDP) and ternary (eukaryotic initiation factor 2 X GTP X met-tRNAf) complex formation. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)32679-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] 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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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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Grace M, Ralston RO, Banerjee AC, Gupta NK. Protein synthesis in rabbit reticulocytes: characteristics of the protein factor RF that reverses inhibition of protein synthesis in heme-deficient reticulocyte lysates. Proc Natl Acad Sci U S A 1982; 79:6517-21. [PMID: 6959132 PMCID: PMC347158 DOI: 10.1073/pnas.79.21.6517] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
During heme deficiency in reticulocyte lysates, the heme-regulated translational inhibitor of protein synthesis (HRI) is activated and shuts off protein synthesis. In partial reactions, HRI phosphorylates the Mr 38,000 subunit (alpha subunit) of eukaryotic initiation factor 2 (eIF-2), which forms a ternary complex, Met-tRNAf X eIF-2 X GTP. The eIF-2 alpha (P) thus formed is not recognized by two eIF-2 ancillary factors, Co-eIF-2B (which promotes the dissociation of the ternary complex at high Mg2+) and Co-eIF-2C (which reverses the inhibition of ternary complex formation), and thus, is presumably inactive in peptide chain initiation. A protein factor, designated RF, which reverses inhibition of protein synthesis in heme-deficient reticulocyte lysates, has been purified from reticulocyte cell supernatant. RF is a high molecular weight (Mr approximately equal to 450,000) protein complex composed of multiple polypeptides. An active RF preparation contains Co-eIF-2B and Co-eIF-2C activities, and these two activities in RF preparation are not inhibited by HRI and ATP--i.e., eIF-2 alpha (P) is recognized. During purification, RF remains associated with eIF-2 activity (eIF-2 X RF) and can be freed of this eIF-2 activity by CM-Sephadex chromatography. Both eIF-2 X RF and RF contain a Mr 38,000 polypeptide component that is indistinguishable from the Mr 38,000 subunit of eIF-2 by two-dimensional gel electrophoresis. It has been observed that a significant part of this Mr 38,000 polypeptide component in eIF-2 X RF and almost the entire Mr 38,000 polypeptide component in RF remain unphosphorylated after prolonged incubation with HRI and ATP. A possible role of this free Mr 38,000 polypeptide in RF action is discussed.
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Bagchi MK, Banerjee AC, Roy R, Chakrabarty I, Gupta NK. Protein synthesis in rabbit reticulocytes: characteristics of CO-eIF-2 protein complex. Nucleic Acids Res 1982; 10:6501-10. [PMID: 6924750 PMCID: PMC326939 DOI: 10.1093/nar/10.20.6501] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
A high molecular weight reticulocyte protein factor, named Co-eIF-2, contains Co-eIF-2A, Co-eIF-2B, and Co-eIF-2C activities and stimulates Met-tRNAf binding to eIF-2 both in the presence and absence of Mg2+. Some characteristics of this stimulation in the absence of Mg2+ are: (1) Stimulation is most pronounced at low eIF-2 levels. (2) Stimulation is partially resistant to heat and NEM treatment, and thus appears to be due to the combined action of both heat and NEM-insensitive Co-eIF-2A, and heat and NEM-sensitive Co-eIF-2C activities. (3) [3H]GDP bound in eIF-2 . [3H]GDP complex is rapidly displaced by unlabelled GTP during ternary complex formation Co-eIF-2 stimulates Met-tRNAf binding to eIF-2 even when added after the [3H]GDP from eIF-2 . [3H]GDP has been completely displaced. This indicates that Co-eIF-2-stimulation is not due to GDP displacement from eIF-2 . GDP. We propose that eIF-2 molecules become inactive in the presence of Mg2+ and at high dilution, and Co-eIF-2 restores the inactive eIF-2 molecules into an active form.
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Ranu RS. Regulation of protein synthesis in rabbit reticulocyte lysates: effect of of Ca2+, Mg2+, and Mn2+ on self-phosphorylation and heterophosphorylation catalyzed by the heme-regulated and double-stranded-RNA-activated protein kinases. Biosci Rep 1982; 2:813-7. [PMID: 7171744 DOI: 10.1007/bf01114941] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The influence of divalent cations Mg2+, Mn2+, and Ca2+ on the cyclic-AMP-independent protein kinases of the heme-regulated and double-stranded-RNA-activated translational inhibitory protein kinases on self-phosphorylation and heterophosphorylation of the substrate (the 38 000-dalton subunit of initiation factor eIF-2) has been examined. Results show that Mg2+, Mn2+, and Ca2+ affect the activities of these enzymes in the following fashion. Mg2+ supports both self-phosphorylation and heterophosphorylation efficiently. Mn2+ on the other hand supports self-phosphorylation but to a lesser degree the heterophosphorylation. Ca2+ promotes neither self-phosphorylation nor heterophosphorylation.
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Feinberg B, McLaughlin CS, Moldave K. Analysis of temperature-sensitive mutant ts 187 of Saccharomyces cerevisiae altered in a component required for the initiation of protein synthesis. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)33902-4] [Citation(s) in RCA: 29] [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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34
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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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35
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Kaplansky DA, Kwan A, Gross M. Effect of Met-tRNAf deacylase on polypeptide chain initiation in rabbit reticulocyte lysate. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(19)83838-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [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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Studies on the mechanism of action of a eukaryotic codon-dependent factor specific for initiator Met-tRNAf and ribosomal 40 S subunits. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)34608-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Siekierka J, Mauser L, Ochoa S. Mechanism of polypeptide chain initiation in eukaryotes and its control by phosphorylation of the alpha subunit of initiation factor 2. Proc Natl Acad Sci U S A 1982; 79:2537-40. [PMID: 6953412 PMCID: PMC346234 DOI: 10.1073/pnas.79.8.2537] [Citation(s) in RCA: 118] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Earlier, we isolated eukaryotic initiation factor 2 (eIF-2)-stimulating protein (SP) as a homogeneous complex with eIF-2 (eIF-2-SP) and showed that, in the presence of Mg2+, eIF-2-SP promotes formation of a ternary complex with GTP and eukaryotic initiator methionyl tRNA (Met-tRNAi) (eIF-2-GTP-Met-tRNAi) catalytically. We now show that SP-bound eIF-2 exchanges with eIF-2 (eIF-2 exchange). Furthermore, in the presence of Mg2+, eIF-2-SP catalyzes the exchange of eIF-2-bound [3H]GDP with unlabeled GDP or GTP (GDP exchange) and the release of [3H]GDP when the ternary complex is formed from eIF-2-[3H]GDP, GTP, and [35S]Met-tRNAi. All these reactions are blocked by alpha-subunit, but not by beta-subunit, phosphorylation of eIF-2. The eIF-2 and GDP exchanges are compatible with the reaction eIF-2-GDP + SP in equilibrium EIF-2-SP + GDP reminiscent of the exchange between the Tu and Ts components of prokaryotic elongation factor 1 (EF-Tu and EF-Ts, respectively) EF-Tu-GDP + EF-Ts in equilibrium EF-Tu-EF-Ts + GDP. Due to the high affinity of GDP (approximately 100 times greater than that of GDP) for eIF-2, 40S (eIF-2-GTP-Met-tRNAi-40S) to 80S (Met-tRNAi-mRNA-80S) initiation complex conversion, which is accompanied by GTP hydrolysis, probably releases eIF-2 as eIF-2-GDP. Our results suggest that, in the presence of Mg2+, GDP binding restricts the availability of eIF-2 for chain initiation and that SP relieves this restriction in a catalytic fashion, provided that the alpha subunit of eIF-2 is not phosphorylated.
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Leroux A, London IM. Regulation of protein synthesis by phosphorylation of eukaryotic initiation factor 2 alpha in intact reticulocytes and reticulocyte lysates. Proc Natl Acad Sci U S A 1982; 79:2147-51. [PMID: 6954531 PMCID: PMC346147 DOI: 10.1073/pnas.79.7.2147] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Studies in intact rabbit reticulocytes and reticulocyte lysates provide further evidence of a functional role for the phosphorylation of eukaryotic initiation factor 2 alpha (eIF-2 alpha) in the regulation of initiation of protein synthesis in eukaryotic cells. In intact reticulocytes treated with isonicotinic acid hydrazide to inhibit heme synthesis, the phosphorylation of eIF-2 alpha was significantly greater than in control cells. In heme-deficient reticulocyte lysates and in lysates treated with double-stranded RNA, significant phosphorylation of eIF-2 alpha occurred prior to the onset of inhibition of protein synthesis; a large proportion, however, of the total eIF-2 alpha remained unphosphorylated. These findings indicate that a modest concentration of phosphorylated eIF-2 alpha can suffice to inhibit initiation, and they suggest that one of the factors with which eIF-2 must interact may be rate limiting, especially when eIF-2 alpha is phosphorylated.
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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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40
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Centrella M, Lucas-Lenard J. Regulation of protein synthesis in vesicular stomatitis virus-infected mouse L-929 cells by decreased protein synthesis initiation factor 2 activity. J Virol 1982; 41:781-91. [PMID: 6284970 PMCID: PMC256815 DOI: 10.1128/jvi.41.3.781-791.1982] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Infection of mouse L-cell spinner cultures by vesicular stomatitis virus (VSV) effected the selective translation of viral mRNA by 4h after viral adsorption. Cell-free systems prepared from mock- and VSV-infected cells reflected this phenomenon; protein synthesis was reduced in the virus-infected cell lysate by approximately 75% compared with the mock-infected (control) lysate. This effect appeared to be specific to protein synthesis initiation since (i) methionine incorporation into protein from an exogenous preparation of initiator methionyl-tRNA gave completely analogous results and (ii) the addition of a ribosomal salt wash (containing protein synthesis initiation factors) stimulated protein synthesis by the infected cell lysate but had no effect on protein synthesis by the control. Micrococcal nuclease-treated (initiation-dependent) VSV-infected cell lysates were not able to translate L-cell mRNA unless they were supplemented with a ribosomal salt wash; a salt wash from ribosomes from uninfected cells effected a quicker recovery than a salt wash from ribosomes from infected cells. When salt wash preparations from ribosomes from uninfected and infected cells were tested for initiation factor 2 (eIF-2)-dependent ternary complex capacity with added GTP and initiator methionyl-tRNA, we found that the two preparations contained equivalent levels of eIF-2. However, initiation complex formation by the factor from virus-infected cells proceeded at a reduced initial rate compared with the control. When the lysates were supplemented with a partially purified eIF-2 preparation, recovery of activity by the infected cell lysate was observed. Mechanisms by which downward regulation of eIF-2 activity might direct the selective translation of viral mRNA in VSV-infected cells are proposed.
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Das A, Bagchi M, Ghosh-Dastidar P, Gupta N. Protein synthesis in rabbit reticulocytes. A study of peptide chain initiation using native and beta-subunit-depleted eukaryotic initiation factor 2. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(19)68188-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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42
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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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43
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Sen GC. Mechanism of interferon action: progress toward its understanding. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1982; 27:105-56. [PMID: 6179128 DOI: 10.1016/s0079-6603(08)60599-1] [Citation(s) in RCA: 68] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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44
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Sharma RK. Cyclic nucleotide control of protein kinases. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1982; 27:233-88. [PMID: 6285418 DOI: 10.1016/s0079-6603(08)60602-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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45
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Gupta NK. Roles of eukaryotic initiation factor 2 ancillary factors in the regulation of eukaryotic protein synthesis initiation. CURRENT TOPICS IN CELLULAR REGULATION 1982; 21:1-33. [PMID: 6754267 DOI: 10.1016/b978-0-12-152821-8.50005-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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46
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Hronis T, Traugh J. The use of porphyrins as probes to examine the requirement for hemin in the maintenance of protein synthesis in reticulocyte lysates. J Biol Chem 1981. [DOI: 10.1016/s0021-9258(19)68412-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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47
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Austin SA, Clemens MJ. The effects of haem on translational control of protein synthesis in cell-free extracts from fed and lysine-derived Ehrlich ascites tumour cells. EUROPEAN JOURNAL OF BIOCHEMISTRY 1981; 117:601-7. [PMID: 6793361 DOI: 10.1111/j.1432-1033.1981.tb06380.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
1. Addition of haem to cell-free extracts from Ehrlich ascites tumour cells stimulates protein synthesis only in extracts from cells previously incubated in nutritionally complete conditions. Extracts from amino-acid-deprived cells do not respond to haem. The stimulation of protein synthesis in fed cell extracts is due to increased initiation on endogenous mRNA mediated by an increase in the levels of 40-S-subunit X Met-tRNA initiation complexes. Extracts from starved cells exhibit a defect in 40-S initiation complex formation which cannot be overcome by haem. 2. Experiments to test for the presence of an inhibitor of initiation in Ehrlich cell extracts by monitoring effects on translation in haem-supplemented reticulocyte lysates have revealed that extracts from both fed and starved cells contain one or more inhibitory activities which shut off protein synthesis, dissagregate polysomes and reduce the level of 40-S initiation complexes in the lysate. Extracts from starved cells are more inhibitory for protein synthesis than those from fed cells. 3. Initiation factor eIF-2 is phosphorylated by an endogenous Ehrlich cell protein kinase in vitro, but this occurs to the same extent in extracts from fed and starved cells. 4. We propose a possible model for the role of eIF-2 in the control of protein synthesis by amino acid supply in Ehrlich cells.
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Mitsui K, Datta A, Ochoa S. Removal of beta subunit of the eukaryotic polypeptide chain initiation factor 2 by limited proteolysis. Proc Natl Acad Sci U S A 1981; 78:4128-32. [PMID: 7027253 PMCID: PMC319741 DOI: 10.1073/pnas.78.7.4128] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
It is generally considered that the eukaryotic polypeptide chain initiation factor 2 (eIF-2) from rabbit reticulocytes consists of three nonidentical subunits termed alpha, beta, and gamma, in order of increasing molecular weight. However, a recent report [Stringer, E. A., Chaudhuri, A., Valenzuela, D. & Maitra, U. (1980) Proc. Natl. Acad. Sci. USA 77, 3356-3359] suggested that this factor is made up of only two subunits. In this paper we show that limited proteolysis of rabbit reticulocyte eIF-2 leads to loss of the beta subunit. This modified eIF-2 has the same activity as the native factor in promoting ternary (eIF-2.GTP.Met-tRNAi) and 40S (eIF-2.GTP.Met-tRNAi.40S ribosome) initiation complex formation. Like native eIF-2, the protease-treated factor can restore translation in heme-deficient lysates. On the other hand, the treated factor is less stable than the native protein.
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Das H, Das A, Ghosh-Dastidar P, Ralston R, Yaghmai B, Roy R, Gupta N. Protein synthesis in rabbit reticulocytes. Purification and characterization of a double-stranded RNA-dependent protein synthesis inhibitor from reticulocyte lysates. J Biol Chem 1981. [DOI: 10.1016/s0021-9258(19)69192-1] [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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50
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Roy R, Ghosh-Dastidar P, Das A, Yaghmai B, Gupta N. Protein synthesis in rabbit reticulocytes. Co-eIF-2A reverses mRNA inhibition of ternary complex (Met-tRNAf.eIF-2.GTP) formation by eIF-2. J Biol Chem 1981. [DOI: 10.1016/s0021-9258(19)69310-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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