Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In eukaryotes the majority of mRNAs have an m(7)G cap that is added cotranscriptionally and that plays an important role in many aspects of mRNA metabolism. The nuclear cap-binding complex (CBC; consisting of CBP20 and CBP80) mediates the stimulatory functions of the cap in pre-mRNA splicing, 3' end formation, and U snRNA export. As little is known about how nuclear CBC mediates the effects of the cap in higher eukaryotes, we have characterized proteins that interact with CBC in HeLa cell nuclear extracts as potential mediators of its function. Using cross-linking and coimmunoprecipitation, we show that eukaryotic translation initiation factor 4G (eIF4G), in addition to its function in the cytoplasm, is a nuclear CBC-interacting protein. We demonstrate that eIF4G interacts with CBC in vitro and that, in addition to its cytoplasmic localization, there is a significant nuclear pool of eIF4G in mammalian cells in vivo. Immunoprecipitation experiments suggest that, in contrast to the cytoplasmic pool, much of the nuclear eIF4G is not associated with eIF4E (translation cap binding protein of eIF4F) but is associated with CBC. While eIF4G stably associates with spliceosomes in vitro and shows close association with spliceosomal snRNPs and splicing factors in vivo, depletion studies show that it does not participate directly in the splicing reaction. Taken together the data indicate that nuclear eIF4G may be recruited to pre-mRNAs via its interaction with CBC and accompanies the mRNA to the cytoplasm, facilitating the switching of CBC for eIF4F. This may provide a mechanism to couple nuclear and cytoplasmic functions of the mRNA cap structure.
Mol Cell Biol 2001 Jun
PMID:Interaction of eukaryotic translation initiation factor 4G with the nuclear cap-binding complex provides a link between nuclear and cytoplasmic functions of the m(7) guanosine cap. 1134 Jan 57

The cDNA sequence of eukaryotic translation initiation factor eIF4E was derived from a Spodoptera frugiperda cDNA library. Eight tryptophan residues, typical for eIF4E, are strictly conserved in the encoded 210 amino acid protein. A polyclonal antiserum detected a 26 kDa protein in lepidopteran cell lines, but not in dipteran cells. Sf21 cells have a single eIF4E gene copy, which is transcribed into a 1500 nt transcript. Infection with AcMNPV resulted in a decrease in eIF4E mRNA starting between 12 and 24 h postinfection (p.i.), while reduced eIF4E protein levels were observed at 48 h p.i. Two forms of eIF4E were recognized that differed in their iso-electric point, of which the relative abundance did not change during infection. Mutagenesis experiments using recombinant baculoviruses revealed that the variation in mobility between these two forms did not result from a difference in the phosphorylation state of Ser-202, the serine residue that corresponds with the eIF4E phosphorylation site in mammalian eIF4E.
Insect Mol Biol 2001 Jun
PMID:Effect of baculovirus infection on the mRNA and protein levels of the Spodoptera frugiperda eukaryotic initiation factor 4E. 1143 17

The translation of mRNA in eukaryotic cells is regulated by amino acids through multiple mechanisms. One such mechanism involves activation of mTOR (Fig. 1). mTOR controls a myriad of downstream effectors, including RNA polymerase I, S6K1, 4E-BP1, and eEF2 kinase. In yeast, and probably in higher eukaryotes, mTOR signals through Tap42p/alpha 4 to regulate protein phosphatases. Through phosphorylation of Tap42p/alpha 4, mTOR abrogates dephosphorylation of the downstream effectors by PP2 A and/or PP6, resulting in their increased phosphorylation. Although at this time still speculative, in vitro results using mTOR immunoprecipitates suggest that mTOR, or an associated kinase, may also be directly involved in phosphorylating some effectors. Enhanced RNA polymerase I activity results in increased transcription of rDNA genes, whereas increased S6K1 activity promotes preferential translation of TOP mRNAs, such as those encoding ribosomal proteins. Together, stimulated RNA polymerase I and S6K1 activities enhance ribosome biogenesis, increasing the translational capacity of the cell. Phosphorylation of 4E-BP1 prohibits its association with eIF4E, allowing eIF4E to bind to eIF4G and form the active eIF4F complex. Increased eIF4F formation preferentially stimulates translation of mRNAs containing long, highly-structured 5' UTRs. Finally, amino acids cause inhibition of the eEF2 kinase, resulting in an increase in the proportion of eEF2 in the active, dephosphorylated form. By inhibiting eEF2 phosphorylation, amino acids may not only stimulate translation elongation, but may also prevent activation of GCN2 by enhancing the rate of removal of deacylated tRNA from the P-site on the ribosome; a potential activator of GCN2. GCN2 may also be regulated directly by the accumulation of deacylated-tRNA caused by treatment with inhibitors of tRNA synthetases or in cells incubated in the absence of essential amino acids. However, because the Km of the tRNA synthetases for amino acids is well above the amino acid concentrations found in plasma of fasted animals, such a mechanism may not be operative in mammals in vivo. Activation of GCN2 results in increased phosphorylation of the alpha-subunit of eIF2, which in turn causes inhibition of eIF2B. Thus, by preventing activation of GCN2, amino acids preserve eIF2B activity, which promotes translation of all mRNAs, i.e., global protein synthesis is enhanced.
Prog Mol Subcell Biol 2001
PMID:Regulation of translation initiation by amino acids in eukaryotic cells. 1157 65

The promyelocytic leukemia protein (PML) is a mammalian regulator of cell growth which is characteristically disrupted in acute promyelocytic leukemia and by a variety of viruses. PML contains a RING domain which is required for its growth-suppressive and antiviral properties. Although normally nuclear, in certain pathogenic conditions, including arenaviral infection, PML is relocated to the cytoplasm, where its functions are poorly understood. Here, we observe that PML and arenavirus protein Z use regions around the first zinc-binding site of their respective RING domains to directly interact, with sub-micromolar affinity, with the dorsal surface of translation initiation factor eIF4E, representing a novel mode of eIF4E recognition. PML and Z profoundly reduce the affinity of eIF4E for its substrate, the 5' 7-methyl guanosine cap of mRNA, by over 100-fold. Association with the dorsal surface of eIF4E and direct antagonism of mRNA cap binding by PML and Z lead to direct inhibition of translation. These activities of the RING domains of PML and Z do not involve ubiquitin-mediated protein degradation, in contrast to many RINGs which have been observed to do so. Although PML and Z have well characterized physiological functions in regulation of growth and apoptosis, this work establishes the first discrete biochemical mechanism which underlies the biological activities of their RING domains. Thus, we establish PML and Z as translational repressors, with potential contributions to the pathogenesis of acute promyelocytic leukemia and variety of viral infections.
J Mol Biol 2001 Sep 28
PMID:The RING domains of the promyelocytic leukemia protein PML and the arenaviral protein Z repress translation by directly inhibiting translation initiation factor eIF4E. 1157 18

The major pathway of eukaryotic mRNA decay involves deadenylation-dependent decapping followed by 5' to 3' exonucleolytic degradation. By examining interactions among mRNA decay factors, the mRNA, and key translation factors, we have identified a critical transition in mRNP organization that leads to decapping and degradation of yeast mRNAs. This transition occurs after deadenylation and includes loss of Pab1p, eIF4E, and eIF4G from the mRNA and association of the decapping activator complex, Lsm1p-7p, which enhances the coimmunoprecipitation of a decapping enzyme complex (Dcp1p and Dcp2p) with the mRNA. These results define an important rearrangement in mRNP organization and suggest that deadenylation promotes mRNA decapping by both the loss of Pab1p and the recruitment of the Lsm1p-7p complex.
Mol Cell 2001 Nov
PMID:Targeting an mRNA for decapping: displacement of translation factors and association of the Lsm1p-7p complex on deadenylated yeast mRNAs. 1174 42

Environmental stress-induced phosphorylation of eIF2alpha inhibits protein translation by reducing the availability of eIF2-GTP-tRNA(i)Met, the ternary complex that joins initiator tRNA(Met) to the 43S preinitiation complex. The resulting untranslated mRNA is dynamically routed to discrete cytoplasmic foci known as stress granules (SGs), a process requiring the related RNA-binding proteins TIA-1 and TIAR. SGs appear to be in equilibrium with polysomes, but the nature of this relationship is obscure. We now show that most components of the 48S preinitiation complex (i.e., small, but not large, ribosomal subunits, eIF3, eIF4E, eIF4G) are coordinately recruited to SGs in arsenite-stressed cells. In contrast, eIF2 is not a component of newly assembled SGs. Cells expressing a phosphomimetic mutant (S51D) of eIF2alpha assemble SGs of similar composition, confirming that the recruitment of these factors is a direct consequence of blocked translational initiation and not due to other effects of arsenite. Surprisingly, phospho-eIF2alpha is recruited to SGs that are disassembling in cells recovering from arsenite-induced stress. We discuss these results in the context of a translational checkpoint model wherein TIA and eIF2 are functional antagonists of translational initiation, and in which lack of ternary complex drives SG assembly.
Mol Biol Cell 2002 Jan
PMID:Evidence that ternary complex (eIF2-GTP-tRNA(i)(Met))-deficient preinitiation complexes are core constituents of mammalian stress granules. 1180 33

Eukaryotic translation initiation factor 3 (eIF3) is a multisubunit complex that plays a central role in translation initiation. We show that fission yeast Sum1, which is structurally related to known eIF3 subunits in other species, is essential for translation initiation, whereas its overexpression results in reduced global translation. Sum1 is associated with the 40S ribosome and interacts stably with Int6, an eIF3 component, in vivo, suggesting that Sum1 is a component of the eIF3 complex. Sum1 is cytoplasmic under normal growth conditions. Surprisingly, Sum1 is rapidly relocalized to cytoplasmic foci after osmotic and thermal stress. Int6 and p116, another putative eIF3 subunit, behave similarly, suggesting that eIF3 is a dynamic complex. These cytoplasmic foci, which additionally comprise eIF4E and RNA components, may function as translation centers during environmental stress. After heat shock, Sum1 additionally colocalizes stably with the 26S proteasome at the nuclear periphery. The relationship between Sum1 and the 26S proteasome was further investigated, and we find cytoplasmic Sum1 localization to be dependent on the 26S proteasome. Furthermore, Sum1 interacts with the Mts2 and Mts4 components of the 26S proteasome. These data indicate a functional link between components of the structurally related eIF3 translation initiation and 26S proteasome complexes.
Mol Biol Cell 2002 May
PMID:Sum1, a component of the fission yeast eIF3 translation initiation complex, is rapidly relocalized during environmental stress and interacts with components of the 26S proteasome. 1200 58

In eukaryotic cells, protein synthesis is regulated by a set of initiation factors (eIF) that are required for recruiting the 40 S ribosomal subunit onto the mRNA molecule. Among these proteins, eIF4GI, which is targeted by picornaviral proteases, makes a bridge between the mRNA cap structure (via eIF4E) and the 40 S ribosome (via eIF3). Recently, internal ribosome entry segment (IRES) elements have been characterized in the genomic RNA of both simian immunodeficiency virus (SIV) and human immunodeficiency virus type 1 (HIV-1), suggesting that viral expression of these two viruses can be regulated at the translational level. Thus, by analogy with members of the picornavirus family, we have investigated the action of the HIV-1 protease on initiation factors eIF4GI and eIF4GII using cell extracts and the rabbit reticulocyte lysate system. Our results show that eIF4GI, but not eIF4GII, is substrate for HIV-1 protease and this effect can be prevented by a HIV-1 protease inhibitor, palinavir. However, in contrast to picornaviral proteases, the cleavage of eIF4GI by HIV-1 protease occurs at multiple sites and impairs translation of both cap-dependent and IRES-containing RNAs, except for the HCV IRES, which does not require eIF4GI or eIF4GII for activity.
J Mol Biol 2002 Apr 19
PMID:In vitro cleavage of eIF4GI but not eIF4GII by HIV-1 protease and its effects on translation in the rabbit reticulocyte lysate system. 1205 64

Decapping by Dcp1 in Saccharomyces cerevisiae is a key step in mRNA degradation. However, the cap also binds the eukaryotic initiation factor (eIF) complex 4F and its associated proteins. Characterisation of the relationship between decapping and interactions involving eIF4F is an essential step towards understanding polysome disassembly and mRNA decay. Three types of observation suggest how changes in the functional status of eIF4F modulate mRNA stability in vivo. First, partial disruption of the interaction between eIF4E and eIF4G, caused by mutations in eIF4E or the presence of the yeast 4E-binding protein p20, stabilised mRNAs. The interactions of eIF4G and p20 with eIF4E may therefore act to modulate the decapping process. Since we also show that the in vitro decapping rate is not directly affected by the nature of the body of the mRNA, this suggests that changes in eIF4F structure could play a role in triggering decapping during mRNA decay. Second, these effects were seen in the absence of extreme changes in global translation rates in the cell, and are therefore relevant to normal mRNA turnover. Third, a truncated form of eIF4E (Delta196) had a reduced capacity to inhibit Dcp1-mediated decapping in vitro, yet did not change cellular mRNA half-lives. Thus, the accessibility of the cap to Dcp1 in vivo is not simply controlled by competition with eIF4E, but is subject to switching between molecular states with different levels of access.
J Mol Biol 2002 May 10
PMID:Modulation of eukaryotic mRNA stability via the cap-binding translation complex eIF4F. 1205 93

mRNA 5'-cap recognition by the eukaryotic translation initiation factor eIF4E has been exhaustively characterized with the aid of a novel fluorometric, time-synchronized titration method, and X-ray crystallography. The association constant values of recombinant eIF4E for 20 different cap analogues cover six orders of magnitude; with the highest affinity observed for m(7)GTP (approximately 1.1 x 10(8) M(-1)). The affinity of the cap analogues for eIF4E correlates with their ability to inhibit in vitro translation. The association constants yield contributions of non-covalent interactions involving single structural elements of the cap to the free energy of binding, giving a reliable starting point to rational drug design. The free energy of 7-methylguanine stacking and hydrogen bonding (-4.9 kcal/mol) is separate from the energies of phosphate chain interactions (-3.0, -1.9, -0.9 kcal/mol for alpha, beta, gamma phosphates, respectively), supporting two-step mechanism of the binding. The negatively charged phosphate groups of the cap act as a molecular anchor, enabling further formation of the intermolecular contacts within the cap-binding slot. Stabilization of the stacked Trp102/m(7)G/Trp56 configuration is a precondition to form three hydrogen bonds with Glu103 and Trp102. Electrostatically steered eIF4E-cap association is accompanied by additional hydration of the complex by approximately 65 water molecules, and by ionic equilibria shift. Temperature dependence reveals the enthalpy-driven and entropy-opposed character of the m(7)GTP-eIF4E binding, which results from dominant charge-related interactions (DeltaH degrees =-17.8 kcal/mol, DeltaS degrees= -23.6 cal/mol K). For recruitment of synthetic eIF4GI, eIF4GII, and 4E-BP1 peptides to eIF4E, all the association constants were approximately 10(7) M(-1), in decreasing order: eIF4GI>4E-BP1>eIF4GII approximately 4E-BP1(P-Ser65) approximately 4E-BP1(P-Ser65/Thr70). Phosphorylation of 4E-BP1 at Ser65 and Thr70 is insufficient to prevent binding to eIF4E. Enhancement of the eIF4E affinity for cap occurs after binding to eIF4G peptides.
J Mol Biol 2002 Jun 07
PMID:Biophysical studies of eIF4E cap-binding protein: recognition of mRNA 5' cap structure and synthetic fragments of eIF4G and 4E-BP1 proteins. 1205 59


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