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Nahum Sonenberg - One of the best experts on this subject based on the ideXlab platform.
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Translational Homeostasis via the mRNA Cap-Binding Protein, eIF4E
Molecular cell, 2012Co-Authors: Akiko Yanagiya, Eigo Suyama, Hironori Adachi, Yuri V. Svitkin, Pedro Aza-blanc, Hiroaki Imataka, Satoshi Mikami, Yvan Martineau, Ze'ev Ronai, Nahum SonenbergAbstract:Translational control of gene expression plays a key role in many biological processes. Consequently, the activity of the translation apparatus is under tight homeostatic control. eIF4E, the mRNA 5' Cap-Binding Protein, facilitates Cap-dependent translation and is a major target for translational control. eIF4E activity is controlled by a family of repressor Proteins, termed 4E-Binding Proteins (4E-BPs). Here, we describe the surprising finding that despite the importance of eIF4E for translation, a drastic knockdown of eIF4E caused only minor reduction in translation. This conundrum can be explained by the finding that 4E-BP1 is degraded in eIF4E-knockdown cells. Hypophosphorylated 4E-BP1, which binds to eIF4E, is degraded, whereas hyperphosphorylated 4E-BP1 is refractory to degradation. We identified the KLHL25-CUL3 complex as the E3 ubiquitin ligase, which targets hypophosphorylated 4E-BP1. Thus, the activity of eIF4E is under homeostatic control via the regulation of the levels of its repressor Protein 4E-BP1 through ubiquitination.
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The mRNA 5' Cap-Binding Protein eIF4E and control of cell growth.
Current opinion in cell biology, 1998Co-Authors: Nahum Sonenberg, Anne-claude GingrasAbstract:Abstract Control of gene expression at the translational level is important in cell growth and proliferation. Recent work has identified pathways that transmit signals from extracellular stimuli to several translation components. A key participant in regulation of translation is eIF4E, the mRNA 5′ Cap-Binding Protein. Several signalling pathways impact on the activity of eIF4E. This review will summarise recent findings on the MAP kinase signalling pathway that leads to phosphorylation of eIF4E and on pathways that regulate repression of eIF4E function. A major unresolved question is how the changes in translation modulate cell growth rate, and a working model will be discused.
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tif4631 and tif4632 two yeast genes encoding the high molecular weight subunits of the Cap Binding Protein complex eukaryotic initiation factor 4f contain an rna recognition motif like sequence and carry out an essential function
Molecular and Cellular Biology, 1993Co-Authors: Charles Goyer, Michael Altmann, Han S Lee, A Blanc, Mohanish Deshmukh, John L Woolford, H Trachsel, Nahum SonenbergAbstract:The 5' ends of eukaryotic mRNAs are blocked by a Cap structure, m7GpppX (where X is any nucleotide). The interaction of the Cap structure with a Cap-Binding Protein complex is required for efficient ribosome Binding to the mRNA. In Saccharomyces cerevisiae, the Cap-Binding Protein complex is a heterodimer composed of two subunits with molecular masses of 24 (eIF-4E, CDC33) and 150 (p150) kDa. p150 is presumed to be the yeast homolog of the p220 component of mammalian eIF-4F. In this report, we describe the isolation of yeast gene TIF4631, which encodes p150, and a closely related gene, TIF4632. TIF4631 and TIF4632 are 53% identical overall and 80% identical over a 320-amino-acid stretch in their carboxy-terminal halves. Both Proteins contain sequences resembling the RNA recognition motif and auxiliary domains that are characteristic of a large family of RNA-Binding Proteins. tif4631-disrupted strains exhibited a slow-growth, cold-sensitive phenotype, while disruption of TIF4632 failed to show any phenotype under the conditions assayed. Double gene disruption engendered lethality, suggesting that the two genes are functionally homologous and demonstrating that at least one of them is essential for viability. These data are consistent with a critical role for the high-molecular-weight subunit of putative yeast eIF-4F in translation. Sequence comparison of TIF4631, TIF4632, and the human eIF-4F p220 subunit revealed significant stretches of homology. We have thus cloned two yeast homologs of mammalian p220.
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A fraction of the mRNA 5' Cap-Binding Protein, eukaryotic initiation factor 4E, localizes to the nucleus.
Proceedings of the National Academy of Sciences of the United States of America, 1992Co-Authors: Flavio Lejbkowicz, Charles Goyer, Andre Darveau, Sonia Neron, Real Lemieux, Nahum SonenbergAbstract:The 5' Cap structure m7GpppN (where N is any nucleotide) is a ubiquitous feature of cellular eukaryotic mRNAs. The Cap is multifunctional as it is involved in translation, nucleocytoplasmic transport, splicing, and stabilization of mRNA against 5' exonucleolytic degradation. The Cap Binding Protein, eukaryotic initiation factor 4E (eIF-4E), is a translation initiation factor that binds to the Cap structure and is part of a complex (eIF-4F) that promotes mRNA Binding to ribosomes. Overexpression of eIF-4E in fibroblasts results in cell transformation. To test the hypothesis that some of the biological effects of eIF-4E might be effected by a nuclear function, we determined the cellular distribution of eIF-4E. By means of indirect immunofluorescence experiments using polyclonal and monoclonal antibodies against eIF-4E as well as transfected epitope-tagged eIF-4E, we demonstrate that a fraction of eIF-4E localizes to the nucleus. These results suggest that eIF-4E is also involved in a nuclear function.
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The coat Protein of the yeast double-stranded RNA virus L-A attaches covalently to the Cap structure of eukaryotic mRNA.
Molecular and cellular biology, 1992Co-Authors: A Blanc, Charles Goyer, Nahum SonenbergAbstract:The eukaryotic mRNA 5' Cap structure m7GpppX (where X is any nucleotide) interacts with a number of cellular Proteins. Several of these Proteins were studied in mammalian, yeast, and drosophila cells and found to be involved in translation initiation. Here we describe a novel Cap-Binding Protein, the coat Protein of L-A, a double-stranded RNA virus that is persistently maintained in many Saccharomyces cerevisiae strains. The results also suggest that the coat Protein of a related double-stranded RNA virus (L-BC) is likewise a Cap-Binding Protein. Strikingly, in contrast to the cellular Cap-Binding Proteins, the interaction between the L-A virus coat Protein and the Cap structure is through a covalent bond.
Paula Alepuz - One of the best experts on this subject based on the ideXlab platform.
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the mrna Cap Binding Protein cbc1 is required for high and timely expression of genes by promoting the accumulation of gene specific activators at promoters
Biochimica et Biophysica Acta, 2016Co-Authors: Nikki De Clercq, Elena Garre, Per Sunnerhagen, Daniel A Medina, Jose E Perezortin, Paula AlepuzAbstract:The highly conserved Saccharomyces cerevisiae Cap-Binding Protein Cbc1/Sto1 binds mRNA co-transcriptionally and acts as a key coordinator of mRNA fate. Recently, Cbc1 has also been implicated in transcription elongation and pre-initiation complex (PIC) formation. Previously, we described Cbc1 to be required for cell growth under osmotic stress and to mediate osmostress-induced translation reprogramming. Here, we observe delayed global transcription kinetics in cbc1Δ during osmotic stress that correlates with delayed recruitment of TBP and RNA polymerase II to osmo-induced promoters. Interestingly, we detect an interaction between Cbc1 and the MAPK Hog1, which controls most gene expression changes during osmostress, and observe that deletion of CBC1 delays the accumulation of the activator complex Hot1-Hog1 at osmostress promoters. Additionally, CBC1 deletion specifically reduces transcription rates of highly transcribed genes under non-stress conditions, such as ribosomal Protein (RP) genes, while having low impact on transcription of weakly expressed genes. For RP genes, we show that recruitment of the specific activator Rap1, and subsequently TBP, to promoters is Cbc1-dependent. Altogether, our results indicate that Binding of Cbc1 to the Capped mRNAs is necessary for the accumulation of specific activators as well as PIC components at the promoters of genes whose expression requires high and rapid transcription.
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yeast mrna Cap Binding Protein cbc1 sto1 is necessary for the rapid reprogramming of translation after hyperosmotic shock
Molecular Biology of the Cell, 2012Co-Authors: Elena Garre, Lorena Romerosantacreu, Nikki De Clercq, Nati Blascoangulo, Per Sunnerhagen, Paula AlepuzAbstract:In response to osmotic stress, global translation is inhibited, but the mRNAs encoding stress-protective Proteins are selectively translated to allow cell survival. To date, the mechanisms and factors involved in the specific translation of osmostress-responsive genes in Saccharomyces cerevisiae are unknown. We find that the mRNA Cap-Binding Protein Cbc1 is important for yeast survival under osmotic stress. Our results provide new evidence supporting a role of Cbc1 in translation initiation. Cbc1 associates with polysomes, while the deletion of the CBC1 gene causes hypersensitivity to the translation inhibitor cycloheximide and yields synthetic "sickness" in cells with limiting amounts of translation initiator factor eIF4E. In cbc1Δ mutants, translation drops sharply under osmotic stress, the subsequent reinitiation of translation is retarded, and "processing bodies" containing untranslating mRNAs remain for long periods. Furthermore, osmostress-responsive mRNAs are transcriptionally induced after osmotic stress in cbc1Δ cells, but their rapid association with polysomes is delayed. However, in cells containing a thermosensitive eIF4E allele, their inability to grow at 37oC is suppressed by hyperosmosis, and Cbc1 relocalizes from nucleus to cytoplasm. These data support a model in which eIF4E-translation could be stress-sensitive, while Cbc1-mediated translation is necessary for the rapid translation of osmostress-protective Proteins under osmotic stress.
Dixie J. Goss - One of the best experts on this subject based on the ideXlab platform.
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IDENTIFICATION AND CHARACTERIZATION OF A NOVEL Cap-Binding Protein FROM ARABIDOPSIS THALIANA
The Journal of biological chemistry, 1998Co-Authors: Kelley A. Ruud, Dixie J. Goss, Christopher Kuhlow, Karen S. BrowningAbstract:Abstract Cap-Binding Proteins specifically bind to the 7-methyl guanosine (m7G) functional group at the 5′ end of eukaryotic mRNAs. A novel Arabidopsis thalianaProtein has been identified that has sequence similarity to Cap-Binding Proteins but is clearly a different form of the Protein. The most obvious primary sequence difference is the substitution of two of the eight conserved tryptophan residues with other aromatic amino acids in the novel Protein. Analogous forms of this novel Protein appear to be present in other higher eukaryotes but not in yeast. Analysis of the native and recombinant forms of the novel Protein by retention on m7GTP-Sepharose indicate that it is a functional Cap-Binding Protein. Measurements of the dissociation constant for this Protein indicate that it binds m7GTP 5–20-fold tighter than eukaryotic initiation factor (eIF)(iso)4E. The novel Protein also supports the initiation of translation of Capped mRNA in vitro. Biochemical analysis and yeast two-hybrid data indicate that it interacts with eIF(iso)4G to form a complex. Based on these observations, this Protein appears to be able to function as a Cap-Binding Protein and is given the designation of novel Cap-Binding Protein (nCBP).
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Wheat Germ Poly(A) Binding Protein Enhances the Binding Affinity of Eukaryotic Initiation Factor 4F and (iso)4F for Cap Analogues
Biochemistry, 1998Co-Authors: M L Balasta, Ren J, Dixie J. GossAbstract:Most eukaryotic mRNAs contain a 5‘ Cap (m7GpppX) and a 3‘ poly(A) tail to increase synergistically the translational efficiency. Recently, the poly(A) Binding Protein (PABP) and Cap-Binding Protein...
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Circular Dichroism and Fluorescence Spectroscopy Studies of Wheat Germ Protein Synthesis mRNA Cap Binding Protein
Spectroscopy of Biological Molecules, 1995Co-Authors: Y. Wang, M L Balasta, T. Xiang, M. Sha, D. Friedland, Dixie J. GossAbstract:In eucaryotic Protein synthesis an important regulatory step is the recognition of the 5’ terminal end of mRNA. This region contains a unique “Cap” structure which is a guanosine residue methylated in the 7 position linked through a 5’-5’ triphosphate linkage to the first residue of the mRNA. This Cap structure occurs in all normal eucaryotic mRNA. Recognition of the Cap occurs mainly through Binding of the Cap Binding Protein, eIF-4F. In wheat germ an isoform of this Protein eIF-(iso)4F exists in addition to eIF-4F. eIF-4F consists of a small subunit between 26–28 kDa which specifically recognizes the Cap structure and a larger subunit. Detailed structural information from crystallography is not available and so we have used a variety of spectroscopic techniques to obtain structural information and correlate this information with functional properties of the Protein. We have investigated the conformation of this Protein using circular dichroism and fluorescence spectroscopy. This Protein shows an unusual conformational change with either pH or Binding of Cap residues. Analysis of the CD data using the SELCON program yielded estimates of the secondary structure content. At either acidic or basic pH the Protein has a high alpha helix content in the absence of Cap residue (~40%).
Charles Goyer - One of the best experts on this subject based on the ideXlab platform.
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tif4631 and tif4632 two yeast genes encoding the high molecular weight subunits of the Cap Binding Protein complex eukaryotic initiation factor 4f contain an rna recognition motif like sequence and carry out an essential function
Molecular and Cellular Biology, 1993Co-Authors: Charles Goyer, Michael Altmann, Han S Lee, A Blanc, Mohanish Deshmukh, John L Woolford, H Trachsel, Nahum SonenbergAbstract:The 5' ends of eukaryotic mRNAs are blocked by a Cap structure, m7GpppX (where X is any nucleotide). The interaction of the Cap structure with a Cap-Binding Protein complex is required for efficient ribosome Binding to the mRNA. In Saccharomyces cerevisiae, the Cap-Binding Protein complex is a heterodimer composed of two subunits with molecular masses of 24 (eIF-4E, CDC33) and 150 (p150) kDa. p150 is presumed to be the yeast homolog of the p220 component of mammalian eIF-4F. In this report, we describe the isolation of yeast gene TIF4631, which encodes p150, and a closely related gene, TIF4632. TIF4631 and TIF4632 are 53% identical overall and 80% identical over a 320-amino-acid stretch in their carboxy-terminal halves. Both Proteins contain sequences resembling the RNA recognition motif and auxiliary domains that are characteristic of a large family of RNA-Binding Proteins. tif4631-disrupted strains exhibited a slow-growth, cold-sensitive phenotype, while disruption of TIF4632 failed to show any phenotype under the conditions assayed. Double gene disruption engendered lethality, suggesting that the two genes are functionally homologous and demonstrating that at least one of them is essential for viability. These data are consistent with a critical role for the high-molecular-weight subunit of putative yeast eIF-4F in translation. Sequence comparison of TIF4631, TIF4632, and the human eIF-4F p220 subunit revealed significant stretches of homology. We have thus cloned two yeast homologs of mammalian p220.
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A fraction of the mRNA 5' Cap-Binding Protein, eukaryotic initiation factor 4E, localizes to the nucleus.
Proceedings of the National Academy of Sciences of the United States of America, 1992Co-Authors: Flavio Lejbkowicz, Charles Goyer, Andre Darveau, Sonia Neron, Real Lemieux, Nahum SonenbergAbstract:The 5' Cap structure m7GpppN (where N is any nucleotide) is a ubiquitous feature of cellular eukaryotic mRNAs. The Cap is multifunctional as it is involved in translation, nucleocytoplasmic transport, splicing, and stabilization of mRNA against 5' exonucleolytic degradation. The Cap Binding Protein, eukaryotic initiation factor 4E (eIF-4E), is a translation initiation factor that binds to the Cap structure and is part of a complex (eIF-4F) that promotes mRNA Binding to ribosomes. Overexpression of eIF-4E in fibroblasts results in cell transformation. To test the hypothesis that some of the biological effects of eIF-4E might be effected by a nuclear function, we determined the cellular distribution of eIF-4E. By means of indirect immunofluorescence experiments using polyclonal and monoclonal antibodies against eIF-4E as well as transfected epitope-tagged eIF-4E, we demonstrate that a fraction of eIF-4E localizes to the nucleus. These results suggest that eIF-4E is also involved in a nuclear function.
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The coat Protein of the yeast double-stranded RNA virus L-A attaches covalently to the Cap structure of eukaryotic mRNA.
Molecular and cellular biology, 1992Co-Authors: A Blanc, Charles Goyer, Nahum SonenbergAbstract:The eukaryotic mRNA 5' Cap structure m7GpppX (where X is any nucleotide) interacts with a number of cellular Proteins. Several of these Proteins were studied in mammalian, yeast, and drosophila cells and found to be involved in translation initiation. Here we describe a novel Cap-Binding Protein, the coat Protein of L-A, a double-stranded RNA virus that is persistently maintained in many Saccharomyces cerevisiae strains. The results also suggest that the coat Protein of a related double-stranded RNA virus (L-BC) is likewise a Cap-Binding Protein. Strikingly, in contrast to the cellular Cap-Binding Proteins, the interaction between the L-A virus coat Protein and the Cap structure is through a covalent bond.
Emmett V Schmidt - One of the best experts on this subject based on the ideXlab platform.
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novel regulatory factors interacting with the promoter of the gene encoding the mrna Cap Binding Protein eif4e and their function in growth regulation
Molecular and Cellular Biology, 1998Co-Authors: Kelly A Johnston, Michael Polymenis, Shanping Wang, John A Branda, Emmett V SchmidtAbstract:Regulation of the mRNA Cap Binding Protein (eIF4E) is critical to the control of cellular proliferation since this Protein is the rate-limiting factor in translation initiation and transforms fibroblasts and since eIF4E mutants arrest budding yeast in the G1 phase of the cell cycle (cdc33). We previously demonstrated regulation of eIF4E by altered transcription of its mRNA in serum-stimulated fibroblasts and in response to c-myc. To identify additional factors regulating eIF4E transcription, we used linker-scanning constructs to characterize sites in the promoter of the eIF4E gene required for its expression. Promoter activity was dependent on sites at −5, −25, −45, and −75; the site at −75 included a previously described myc box. Electrophoretic mobility shift assays identified DNA-Protein interactions at −25 and revealed a Binding site (TTACCCCCCCTT) that is unique to the eIF4E promoter. Proteins of 68 and 97 kDa bound this site in UV cross-linking and Southwestern experiments. Levels of 4E regulatory factor activities correlated with c-Myc levels, eIF4E expression levels, and Protein synthesis in differentiating U937 and HL60 cells, suggesting that these activities may function to regulate Protein synthesis rates during differentiation. Since the eIF4E promoter lacked typical TATA and initiator elements, further studies of this novel initiator-homologous element should provide insights into mechanisms of transcription initiation and growth regulation.
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an essential e box in the promoter of the gene encoding the mrna Cap Binding Protein eukaryotic initiation factor 4e is a target for activation by c myc
Molecular and Cellular Biology, 1996Co-Authors: Robin M Jones, Kelly A Johnston, Michael Polymenis, John A Branda, Michele A Gadd, Anil K Rustgi, L Callanan, Emmett V SchmidtAbstract:The mRNA Cap-Binding Protein (eukaryotic initiation factor 4E [eIF4E]) binds the m7 GpppN Cap on mRNA, thereby initiating translation. eIF4E is essential and rate limiting for Protein synthesis. Overexpression of eIF4E transforms cells, and mutations in eIF4E arrest cells in G, in cdc33 mutants. In this work, we identified the promoter region of the gene encoding eIF4E, because we previously identified eIF4E as a potential myc-regulated gene. In support of our previous data, a minimal, functional, 403-nucleotide promoter region of eIF4E was found to contain CACGTG E box repeats, and this core eIF4E promoter was myc responsive in cotransfections with c-myc. A direct role for myc in activating the eIF4E promoter was demonstrated by cotransfections with two dominant negative mutants of c-myc (MycdeltaTAD and MycdeltaBR) which equally suppressed promoter function. Furthermore, electrophoretic mobility shift assays demonstrated quantitative Binding to the E box motifs that correlated with myc levels in the electrophoretic mobility shift assay extracts; supershift assays demonstrated max and USF Binding to the same motif. cis mutations in the core or flank of the eIF4E E box simultaneously altered myc-max and USF Binding and inactivated the promoter. Indeed, mutations of this E box inactivated the promoter in all cells tested, suggesting it is essential for expression of eIF4E. Furthermore, the GGCCACGTG(A/T)C(C/G) sequence is shared with other in vivo targets for c-myc, but unlike other targets, it is located in the immediate promoter region. Its critical function in the eIF4E promoter coupled with the known functional significance of eIF4E in growth regulation makes it a particularly interesting target for c-myc regulation.