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Shagam LI, Terenin IM, Andreev DE, Dunaevsky JE, Dmitriev SE. In vitro activity of human translation initiation factor eIF4B is not affected by phosphomimetic amino acid substitutions S422D and S422E. Biochimie 2012; 94:2484-90. [PMID: 22750809 DOI: 10.1016/j.biochi.2012.06.021] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2012] [Accepted: 06/20/2012] [Indexed: 10/28/2022]
Abstract
Eukaryotic translation initiation factor eIF4B is necessary for ribosomal scanning through structured mRNA leaders. In higher eukaryotes, eIF4B serves as a downstream effector of several signaling pathways. In response to mitogenic stimuli, eIF4B undergoes multiple phosphorylations which are thought to regulate its activity. Recently, Ser422 was identified as a predominant site for human eIF4B phosphorylation via several signaling pathways, and phosphomimetic amino acid substitutions S422D or S422E were shown to activate eIF4B in living cells. However, stimulatory role of these modifications has never been analyzed directly. Here, using both mammalian reconstituted translation initiation assay and complete cell-free translation system, we perform a comparison of recombinant eIF4B derivatives with the wild type recombinant protein, and do not find any difference in their activities. On the contrary, native eIF4B purified from HeLa cells reveals significantly higher activity in both assays. Thus, the effects of S422D and S422E substitutions on eIF4B activity in living cells observed previously either require some other protein modification(s), or may only be manifested in an intact cell. Our study raises the question on whether the phosphorylation of Ser422 is sufficient for eIF4B activation observed upon mitogenic stimulation.
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Affiliation(s)
- Lev I Shagam
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Bldg. A, Leninskie Gory, Moscow 119234, Russia
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2
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Piccioni F, Zappavigna V, Verrotti AC. Translational regulation during oogenesis and early development: the cap-poly(A) tail relationship. C R Biol 2005; 328:863-81. [PMID: 16286077 DOI: 10.1016/j.crvi.2005.05.006] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2005] [Revised: 05/10/2005] [Accepted: 05/10/2005] [Indexed: 11/30/2022]
Abstract
Metazoans rely on the regulated translation of select maternal mRNAs to control oocyte maturation and the initial stages of embryogenesis. These transcripts usually remain silent until their translation is temporally and spatially required during early development. Different translational regulatory mechanisms, varying from cytoplasmic polyadenylation to localization of maternal mRNAs, have evolved to assure coordinated initiation of development. A common feature of these mechanisms is that they share a few key trans-acting factors. Increasing evidence suggest that ubiquitous conserved mRNA-binding factors, including the eukaryotic translation initiation factor 4E (eIF4E) and the cytoplasmic polyadenylation element binding protein (CPEB), interact with cell-specific molecules to accomplish the correct level of translational activity necessary for normal development. Here we review how capping and polyadenylation of mRNAs modulate interaction with multiple regulatory factors, thus controlling translation during oogenesis and early development.
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Affiliation(s)
- Federica Piccioni
- CEINGE-Biotecnologie Avanzate, Via Comunale Margherita 482, 80145 Naples, Italy
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von der Haar T, Gross JD, Wagner G, McCarthy JEG. The mRNA cap-binding protein eIF4E in post-transcriptional gene expression. Nat Struct Mol Biol 2004; 11:503-11. [PMID: 15164008 DOI: 10.1038/nsmb779] [Citation(s) in RCA: 177] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2004] [Accepted: 04/22/2004] [Indexed: 11/09/2022]
Abstract
Eukaryotic initiation factor 4E (eIF4E) has central roles in the control of several aspects of post-transcriptional gene expression and thereby affects developmental processes. It is also implicated in human diseases. This review explores the relationship between structural, biochemical and biophysical aspects of eIF4E and its function in vivo, including both long-established roles in translation and newly emerging ones in nuclear export and mRNA decay pathways.
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Affiliation(s)
- Tobias von der Haar
- Post-transcriptional Control Group, Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, PO Box 88, Manchester M60 1QD, UK.
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4
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Dmitriev SE, Terenin IM, Dunaevsky YE, Merrick WC, Shatsky IN. Assembly of 48S translation initiation complexes from purified components with mRNAs that have some base pairing within their 5' untranslated regions. Mol Cell Biol 2004; 23:8925-33. [PMID: 14645505 PMCID: PMC309656 DOI: 10.1128/mcb.23.24.8925-8933.2003] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The reconstitution of translation initiation complexes from purified components is a reliable approach to determine the complete set of essential canonical initiation factors and auxiliary proteins required for the 40S ribosomal subunit to locate the initiation codon on individual mRNAs. Until now, it has been successful mostly for formation of 48S translation initiation complexes with viral IRES elements. Among cap-dependent mRNAs, only globin mRNAs and transcripts with artificial 5' leaders were amenable to this assembly. Here, with modified conditions for the reconstitution, 48S complexes have been successfully assembled with the 5' UTR of beta-actin mRNA (84 nucleotides) and the tripartite leader of adenovirus RNAs (232 nucleotides), though the latter has been able to use only the scanning rather then the shunting model of translation initiation with canonical initiation factors. We show that initiation factor 4B is essential for mRNAs that have even a rather moderate base pairing within their 5' UTRs (with the cumulative stability of the secondary structure within the entire 5' UTR < -13 kcal/mol) and not essential for beta-globin mRNA. A recombinant eIF4B poorly substitutes for the native factor. The 5' UTRs with base-paired G residues reveal a very sharp dependence on the eIF4B concentration to form the 48S complex. The data suggest that even small variations in concentration or activity of eIF4B in mammalian cells may differentially affect the translation of different classes of cap-dependent cellular mRNAs.
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Affiliation(s)
- Sergei E Dmitriev
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, 119899 Moscow, Russia
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5
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Abstract
Protein synthesis in both eukaryotic and prokaryotic cells is a complex process requiring a large number of macromolecules: initiation factors, elongation factors, termination factors, ribosomes, mRNA, amino-acylsynthetases and tRNAs. This review focuses on our current knowledge of protein synthesis in higher plants.
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Affiliation(s)
- K S Browning
- Department of Chemistry and Biochemistry, University of Texas at Austin 78712, USA
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6
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Abstract
The study of the regulation of initiation of protein synthesis has recently gained momentum because of the established relationship between translation initiation, cell growth and tumorigenesis. Therefore much effort is devoted to the role of protein kinases which are activated in signal transduction cascades and which are responsible for the phosphorylation of a number of initiation factors. These specific factors are mainly involved in the binding of messenger RNA to the 40S ribosome, a process that makes the unwinding of the 5' untranslated region necessary. It appears that the phosphorylation of these factors increases their ability for cap recognition and helicase activity. The enhanced phosphorylation of the messenger binding factors results not only in an overall stimulation of translation, but especially weak messengers are positively discriminated. The above mechanisms mainly deal with qualitative control of translation, i.e., messenger selection, but phosphorylation also plays a role in quantitative regulation of protein synthesis. The generation of active eIF-2, the initiation factor that binds the Met-tRNA(i) and GTP, is dependent on a factor involved in the GDP-GTP exchange. Phosphorylation of eIF-2 results in sequestration of the exchange factor and a slowing down of the rate of initiation.
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Affiliation(s)
- H O Voorma
- Department of Molecular Cell Biology, Utrecht University, The Netherlands
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7
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Wolthuis RM, Cremers AF, Kasperaitis MA, van der Mast C, Voorma HO, Boonstra J. Epidermal growth factor stimulates phosphorylation of eukaryotic initiation factor 4B, independently of protein kinase C. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1177:160-6. [PMID: 8388736 DOI: 10.1016/0167-4889(93)90035-n] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We demonstrate that exposure of human epidermoid carcinoma A431 cells to epidermal growth factor (EGF) results in phosphorylation of eIF-4B within minutes after addition of EGF. The EGF-induced phosphorylation of eIF-4B is not caused by the EGF receptor tyrosine kinase itself, since no tyrosine-phosphorylated eIF-4B could be detected upon immunoprecipitation using an anti-phosphotyrosine antibody. Enhanced phosphorylation of eIF-4B was also detected upon exposure of the cells to phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), suggesting that eIF-4B may be a substrate of PKC. However, down-regulation of PKC did not influence the EGF-induced eIF-4B phosphorylation, which indicates that eIF-4B is phosphorylated by an as yet unknown kinase, activated early in the EGF-induced signal transduction cascade.
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Affiliation(s)
- R M Wolthuis
- Department of Molecular Cell Biology, University of Utrecht, The Netherlands
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8
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Yoder-Hill J, Pause A, Sonenberg N, Merrick W. The p46 subunit of eukaryotic initiation factor (eIF)-4F exchanges with eIF-4A. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53358-5] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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9
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Rhoads RE, Joshi-Barve S, Rinker-Schaeffer C. Mechanism of action and regulation of protein synthesis initiation factor 4E: effects on mRNA discrimination, cellular growth rate, and oncogenesis. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1993; 46:183-219. [PMID: 8234784 DOI: 10.1016/s0079-6603(08)61022-3] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- R E Rhoads
- Department of Biochemistry and Molecular Biology, Louisiana State University Medical Center, Shreveport 71130
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van Heugten HA, Thomas AA, Voorma HO. Interaction of protein synthesis initiation factors with the mRNA cap structure. Biochimie 1992; 74:463-75. [PMID: 1637872 DOI: 10.1016/0300-9084(92)90087-u] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The mechanism of mRNA recognition by proteins interacting with the mRNA cap structure was investigated by photochemical cross-linking of proteins with 32P-labelled reoviral RNAs. Using ribosomal washes as a source of eukaryotic protein synthesis initiation factors, we identified the well-known cap binding proteins eIF-4B and -4E, but eIF-2 and eIF-3 as well. The interplay of purified eIF-4A, -4B, and -4F was studied in relation to ATP dependence and cap analogue sensitivity of cap binding. Next to their well-known roles in the initiation process, eIF-2 and eIF-3 also cross-linked to the 5' cap. eIF-2 stimulated eIF-4B and -4E cross-linking, an observation that has been previously described more extensively. The interaction of eIF-2 with the 5' end of mRNA was extremely sensitive to K(+)-ions and was resistant to a high concentration of Mg(2+)-ions; this influence of mono- and divalent ions was in contrast with the cross-linking of eIF-4B and -4E. Optimal interaction of these factors was obtained at moderate K+ concentration and low Mg(2+)-ion concentrations. eIF-2 cross-linking was sensitive to high protein to mRNA ratios indicating a weak affinity as compared to eIF-4E and -4B. The interaction of eIF-3 with the cap of mRNA is also weak as it was counteracted by all other cap binding proteins, leading to an inability to detect the cross-linking of this protein in crude eIF preparations. Time kinetics of formation of complexes suggested eIF-2 to be one of the first factors to interact with mRNA. Preformed RNA-protein complexes were dissociated after cap analogue addition, suggesting reversible interactions between RNA and proteins.
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Affiliation(s)
- H A van Heugten
- Department of Molecular Cell Biology, University of Utrecht, The Netherlands
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11
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Affiliation(s)
- C G Proud
- Department of Biochemistry, School of Medical Sciences, University of Bristol, England
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12
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Anthony DD, Merrick WC. Analysis of 40 S and 80 S complexes with mRNA as measured by sucrose density gradients and primer extension inhibition. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)45981-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [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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Donaldson RW, Hagedorn CH, Cohen S. Epidermal growth factor or okadaic acid stimulates phosphorylation of eukaryotic initiation factor 4F. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)49968-1] [Citation(s) in RCA: 36] [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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14
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15
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Morley SJ, Traugh JA. Differential stimulation of phosphorylation of initiation factors eIF-4F, eIF-4B, eIF-3, and ribosomal protein S6 by insulin and phorbol esters. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(18)86990-3] [Citation(s) in RCA: 144] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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16
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Tuazon PT, Morley SJ, Dever TE, Merrick WC, Rhoads RE, Traugh JA. Association of initiation factor eIF-4E in a cap binding protein complex (eIF-4F) is critical for and enhances phosphorylation by protein kinase C. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(18)86991-5] [Citation(s) in RCA: 38] [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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17
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Etchison D, Smith K. Variations in cap-binding complexes from uninfected and poliovirus-infected HeLa cells. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39140-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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18
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Duncan RF. Protein synthesis initiation factor modifications during viral infections: implications for translational control. Electrophoresis 1990; 11:219-27. [PMID: 2188834 DOI: 10.1002/elps.1150110305] [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: 12/30/2022]
Abstract
Infection of tissue culture cells with certain viruses results in the shutoff of host cell protein synthesis. We have examined virally infected cell lysates using two-dimensional gel electrophoresis and immunoblotting to ascertain whether initiation factor protein modifications are correlated with translational repression. Moderate increases in eukaryotic initiation factor (eIF)-2 alpha phosphorylation are detected in reovirus- and adenovirus-infected cells, as reported previously (Samuel et al., 1984; O'Malley et al., 1989). Neither vesicular stomatitis virus, vaccinia virus, frog virus III, rhinovirus, nor encephalomyocarditis virus caused significantly increased 2 alpha phosphorylation. There were no reproducible, significant changes in eIF-4A, eIF-4B, or eIF-2 beta in cells infected by any of these viruses. The cleavage of eIF-4F subunit p220, such as has been previously demonstrated to occur in poliovirus (Etchison et al., 1982) and rhinovirus (Etchison and Fout, 1985), was not detected in any of the other virus infections analyzed.
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Affiliation(s)
- R F Duncan
- School of Pharmacy, University of Southern California, Los Angeles 90033
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19
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Lawson TG, Lee KA, Maimone MM, Abramson RD, Dever TE, Merrick WC, Thach RE. Dissociation of double-stranded polynucleotide helical structures by eukaryotic initiation factors, as revealed by a novel assay. Biochemistry 1989; 28:4729-34. [PMID: 2548591 DOI: 10.1021/bi00437a033] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A new technique has been applied to the study of the RNA secondary structure unwinding activity of the eukaryotic initiation factors (eIFs) 4F, 4A, and 4B. Secondary structures were generated at the 5' ends of reovirus and globin mRNA molecules by hybridization with 32P-labeled cDNA molecules 15 nucleotide residues long. The dissociation of the labeled cDNAs from the mRNAs was assayed by a gel filtration chromatography procedure which separates the free cDNAs from mRNAs and mRNA/cDNA hybrids. When the three factors were tested alone, only eIF-4F stimulated dissociation of hybrids. The combination of eIF-4A plus eIF-4B also exhibited a strong hybrid dissociating activity, which was markedly temperature dependent. Under optimum conditions, up to 90% of the hybrid structures are disrupted in 60 min. These results demonstrate for the first time that stable double-stranded regions can be melted and dissociated by eIFs. They also characterize more precisely the first step in the structure unwinding reaction.
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Affiliation(s)
- T G Lawson
- Department of Biology, Washington University, St. Louis, Missouri 63130
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20
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Browning KS, Fletcher L, Lax SR, Ravel JM. Evidence That the 59-kDa Protein Synthesis Initiation Factor from Wheat Germ Is Functionally Similar to the 80-kDa Initiation Factor 4B from Mammalian Cells. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)81817-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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21
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Morley SJ, Traugh JA. Phorbol esters stimulate phosphorylation of eukaryotic initiation factors 3, 4B, and 4F. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)81626-5] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.9] [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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Fawell EH, Boyer IJ, Brostrom MA, Brostrom CO. A Novel Calcium-dependent Phosphorylation of a Ribosome-associated Protein. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)94236-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [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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Translational control in heat-shocked Drosophila embryos. Evidence for the inactivation of initiation factor(s) involved in the recognition of mRNA cap structure. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)37647-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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24
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Milburn SC, Pelletier J, Sonenberg N, Hershey JW. Identification of the 80-kDa protein that crosslinks to the cap structure of eukaryotic mRNAs as initiation factor eIF-4B. Arch Biochem Biophys 1988; 264:348-50. [PMID: 3395129 DOI: 10.1016/0003-9861(88)90604-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Preparations of either crude or purified protein synthesis initiation factors, when tested by crosslinking to the m7G-cap structure of mRNAs, exhibit specific crosslinking to an 80-kDa protein. Polyclonal antibodies specific for eIF-4B precipitate the 80-kDa cap-radiolabeled protein, thereby demonstrating that eIF-4B binds mRNA near its 5'-terminus.
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Affiliation(s)
- S C Milburn
- Department of Biological Chemistry, School of Medicine, University of California, Davis 95616
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25
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Lawson TG, Cladaras MH, Ray BK, Lee KA, Abramson RD, Merrick WC, Thach RE. Discriminatory interaction of purified eukaryotic initiation factors 4F plus 4A with the 5' ends of reovirus messenger RNAs. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68637-5] [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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26
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Abramson RD, Dever TE, Merrick WC. Biochemical evidence supporting a mechanism for cap-independent and internal initiation of eukaryotic mRNA. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68741-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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27
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Abramson RD, Browning KS, Dever TE, Lawson TG, Thach RE, Ravel JM, Merrick WC. Initiation factors that bind mRNA. A comparison of mammalian factors with wheat germ factors. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)60739-2] [Citation(s) in RCA: 36] [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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28
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29
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Sonenberg N. Cap-binding proteins of eukaryotic messenger RNA: functions in initiation and control of translation. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1988; 35:173-207. [PMID: 3065823 DOI: 10.1016/s0079-6603(08)60614-5] [Citation(s) in RCA: 230] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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30
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Buckley B, Ehrenfeld E. The cap-binding protein complex in uninfected and poliovirus-infected HeLa cells. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(19)76470-9] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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31
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Goss DJ, Woodley CL, Wahba AJ. A fluorescence study of the binding of eucaryotic initiation factors to messenger RNA and messenger RNA analogues. Biochemistry 1987; 26:1551-6. [PMID: 3593677 DOI: 10.1021/bi00380a009] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The binding of the eucaryotic polypeptide chain initiation factors (eIFs) 4A, 4B, and 4F to poly(1,N6-ethenoadenylic acid) [poly(epsilon A)] was investigated by fluorescence spectroscopy. Competition experiments allowed us to determine the relative affinity of these proteins for mRNA cap analogues and the triplets AUG, GUG, UUU, UAA, and UGA. The salt dependence of eIF-4A binding to poly(epsilon A) and mRNA suggested that the binding was largely electrostatic and was enhanced in the presence of Mg2+ and ATP. The size of the binding site of eIF-4A, eIF-4B, and eIF-4F on poly(epsilon A) was approximately 13, 25, and 35 nucleotides, respectively. Fluorescence studies with the cap analogue 7-methylguanosine triphosphate as well as competition studies with poly(epsilon A) provide further evidence for a direct interaction of eIF-4F with the cap region. There was no evidence that either eIF-4B or eIF-4A bound the mRNA cap directly. In contrast to the other two factors, eIF-4B was found to bind preferentially to AUG, and of all the triplets tested, AUG was the most effective competitor for poly(epsilon A) binding.
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32
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Abramson R, Dever T, Lawson T, Ray B, Thach R, Merrick W. The ATP-dependent interaction of eukaryotic initiation factors with mRNA. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)61430-9] [Citation(s) in RCA: 90] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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