A wheat germ cap-site factor functional in protein chain initiation

Seal, Samarendra N.; Schmidt, A; Marcus, Abraham; Edery, Isaac; Sonenberg, Nahum

doi:10.1016/0003-9861(86)90327-9

Cited by 32 publications

(10 citation statements)

References 22 publications

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“…This factor has since been correctly identified as an isozyme form of eIF4F and termed elFiso4F (see below, [34]). Another initiation factor was subsequently isolated from wheat germ that has similar enzymatic properties to mammalian eIF4B [39,283]. This initiation factor was named eIF4B by Seal et al [283] and eIF4G by Browning et al [39].…”

Section: Elf4bmentioning

confidence: 99%

The plant translational apparatus

1996

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Section: Elf4bmentioning

confidence: 99%

The plant translational apparatus

1996

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“…The proposed cooperativity between sites may also explain why eIF4F complexes purified from plant (31,47,48), yeast (33), and Drosophila (35) do not contain eIF4A, despite the fact that direct binding of eIF4A to eIF4G can be demonstrated in wheat germ (49,50) and yeast (51,52) and that the affinity of yeast eIF4G for eIF4A ( ϭ 17 nM; Fig. 6).…”

Section: Eif4g-1 Interactions With Eif4amentioning

confidence: 99%

Characterization of the Two eIF4A-binding Sites on Human eIF4G-1

Korneeva¹,

Lamphear²,

Hennigan³

et al. 2001

Journal of Biological Chemistry

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Eukaryotic translation initiation factor 4G-1 (eIF4G) plays a critical role in the recruitment of mRNA to the 43 S preinitiation complex. eIF4G has two binding sites for the RNA helicase eIF4A, one in the central domain and one in the COOH-terminal domain. Recombinant eIF4G fragments that contained each of these sites separately bound eIF4A with a 1:1 stoichiometry, but fragments containing both sites bound eIF4A with a 1:2 stoichiometry. eIF3 did not interfere with eIF4A binding to the central site. Interestingly, at the same concentration of free eIF4A, more eIF4A was bound to an eIF4G fragment containing both eIF4A sites than the sum of binding to fragments containing the single sites, indicating cooperative binding. Binding of eIF4A to an immobilized fragment of eIF4G containing the COOH-terminal site was competed by a soluble eIF4G fragment containing the central site, indicating that a single eIF4A molecule cannot bind simultaneously to both sites. The association rate constant, dissociation rate constant, and dissociation equilibrium constant for each site were determined by surface plasmon resonance and found to be, respectively, 1. The initiation of translation of most eukaryotic mRNAs involves the sequential recruitment of Met-tRNA i , mRNA, and the 60 S ribosomal subunit to the 40 S ribosomal subunit, catalyzed by the various groups of initiation factors (1). One of the most highly regulated steps is the recruitment of mRNA, which requires recognition of the 5Ј-terminal m 7 GTP-containing cap and 3Ј-terminal poly(A) tract, unwinding of 5Ј-terminal secondary structure, and binding to the 43 S initiation complex. These steps are mediated by members of the eIF4 1 group of initiation factors (eIF4A, eIF4B, eIF4E, and eIF4G) as well as poly(A)-binding protein.eIF4A is the prototypical member of the DEXD/H-box protein family of nucleic acid helicases (2, 3). It functions as an ATPdependent, bi-directional RNA helicase and RNA-dependent ATPase (4 -7). The ␥-phosphate on the bound nucleotide has been shown to mediate changes in eIF4A conformation and RNA affinity. ATP binding and hydrolysis produce conformational changes in eIF4A that alter the RNA-protein interactions (8, 9, 3). A current model for protein synthesis initiation envisions eIF4A in the role of unwinding mRNA secondary structure in the 5Ј-untranslated region to allow the 40 S ribosomal subunit to bind the mRNA and/or scan it for the first AUG. The observation that dominant negative variants of eIF4A inhibit translation is consistent with such a role (10). Interestingly, the RNA helicase activity of eIF4A is ϳ20 times greater when bound to eIF4G than as a free protein (6, 11).There are at least two genes for eIF4G in humans (12-14), wheat germ (15), and yeast (16). In mammals, these are termed eIF4G-1 and eIF4G-2.2 eIF4G serves to colocalize initiation factors involved in mRNA recruitment to the 43 S initiation complex. It directly binds RNA (17-19), poly(A)-binding protein (13), eIF4E (20, 21), the 40 S-binding protein complex eIF3 (20), eIF4A (...

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“…Interactions between eIF-4E and other subunits of eIF-4F were evidenced by copurification over sucrose gradients or with affinity chromatography (8,15,35). In some species, such as Saccharomyces cerevisiae or wheat germ, eIF-4A is not present in the eIF-4F complex purified on a cap-affinity column, suggesting a loose association between eIF-4A and the other subunits of the complex (14,22,30). p220 is cleaved upon picornavirus infection (all genera except the cardioviruses and hepatoviruses), and this cleavage correlates with a drastic decrease in cap-dependent translation (9, 32).…”

mentioning

confidence: 99%

The Translation Initiation Factor eIF-4E Binds to a Common Motif Shared by the Translation Factor eIF-4γ and the Translational Repressors 4E-Binding Proteins

Mader

Lee

Pause

et al. 1995

Molecular and Cellular Biology

641

604

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Eukaryotic translation initiation factor 4E (eIF-4E), which possesses cap-binding activity, functions in the recruitment of mRNA to polysomes as part of a three-subunit complex, eIF-4F (cap-binding complex). eIF-4E is the least abundant of all translation initiation factors and a target of growth regulatory pathways. Recently, two human cDNAs encoding novel eIF-4E-binding proteins (4E-BPs) which function as repressors of capdependent translation have been cloned. Their interaction with eIF-4E is negatively regulated by phosphorylation in response to cell treatment with insulin or growth factors. The present study aimed to characterize the molecular interactions between eIF-4E and the other subunits of eIF-4F and to similarly characterize the molecular interactions between eIF-4E and the 4E-BPs. A 49-amino-acid region of eIF-4␥, located in the N-terminal side of the site of cleavage by Picornaviridae protease 2A, was found to be sufficient for interacting with eIF-4E. Analysis of deletion mutants in this region led to the identification of a 12-amino-acid sequence conserved between mammals and Saccharomyces cerevisiae that is critical for the interaction with eIF-4E. A similar motif is found in the amino acid sequence of the 4E-BPs, and point mutations in this motif abolish the interaction with eIF-4E. These results shed light on the mechanisms of eIF-4F assembly and on the translational regulation by insulin and growth factors.A ubiquitous feature of all eukaryotic cellular mRNAs is the presence at their 5Ј end of a cap structure, m7GpppX (where X is any nucleotide). The cap facilitates mRNA binding to ribosomes, a step which is rate limiting in translation (for reviews, see references 18 and 20). The cap is bound by the eukaryotic initiation factor 4F (eIF-4F) protein complex, which consists in mammals of three polypeptides: eIF-4E (a 25-kDa cap-binding protein), eIF-4␥ (also known as p220 in mammals), and eIF-4A (a 46-kDa RNA helicase). eIF-4F, in conjunction with eIF-4B, exhibits RNA helicase activity. Evidence suggests that this activity mediates mRNA unwinding in the vicinity of the cap structure in an ATP-dependent manner and facilitates binding of the 40S ribosomal subunit (26, 33). The 40S subunit is then thought to scan the mRNA in the 5Ј-to-3Ј direction until it encounters the initiator AUG codon. This series of steps constitutes the cap-dependent pathway of translation initiation (26,33).eIF-4E is the least abundant of all translation initiation factors, and its overexpression leads to deregulation of cell growth in HeLa cells (6) and to transformation of NIH 3T3 cells and CHO cells (5, 23) or rat primary fibroblasts, the latter in combination with v-myc or E1A (24). An attractive model for eIF-4E transforming activity is that overexpression of eIF-4E results in increased translation of mRNAs which are normally repressed, such as protooncogene mRNAs. eIF-4E activity is upregulated upon treatment of cells with growth factors, mitogens, and phorbol esters, which correlates with an increase in translatio...

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A wheat germ cap-site factor functional in protein chain initiation

Cited by 32 publications

References 22 publications

The plant translational apparatus

The plant translational apparatus

Characterization of the Two eIF4A-binding Sites on Human eIF4G-1

The Translation Initiation Factor eIF-4E Binds to a Common Motif Shared by the Translation Factor eIF-4γ and the Translational Repressors 4E-Binding Proteins

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