Modulation of the Helicase Activity of eIF4A by eIF4B, eIF4H, and eIF4F

Rogers, George W.; Richter, Nancy J.; Lima, Walt F.; Merrick, William C.

doi:10.1074/jbc.m100157200

Cited by 308 publications

(301 citation statements)

References 48 publications

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“…The eIF4G-induced, half-open form of eIF4A promotes RNA binding and also accelerates phosphate release, which is presumably the rate-limiting step in the ATPase cycle for eIF4A 91 . These findings are consistent with the well-documented stimulation of the RNA-dependent ATPase activity of eIF4A by eIF4G 85 . In addition, full-length eIF4G might also increase binding of eIF4A to RNA by providing additional RNAbinding sites 85 .…”

Section: Nuclear Specklessupporting

confidence: 91%

“…These findings are consistent with the well-documented stimulation of the RNA-dependent ATPase activity of eIF4A by eIF4G 85 . In addition, full-length eIF4G might also increase binding of eIF4A to RNA by providing additional RNAbinding sites 85 . A further study indicated that eIF4G promotes the formation of a complex of eIF4A, eIF4B and RNA 92 .…”

Section: Nuclear Specklessupporting

confidence: 91%

“…However, an appreciable fraction of eIF4A is not bound in eIF4F 77 . eIF4A also associates with the initiation factors eIF4B and eIF4H, which are closely related RNA-binding proteins that enhance eIF4A association with RNA 84 and thereby increase the ability of eIF4A to unwind RNA and hydrolyse ATP in an RNA-stimulated fashion 85,86,87 . Together, these factors all promote formation of a translation initiation complex that allows binding of the small 40S ribosomal unit and other initiation factors to mRNA 88 .…”

Section: Nuclear Specklesmentioning

confidence: 99%

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From unwinding to clamping — the DEAD box RNA helicase family

Linder

Jankowsky

2011

Nat Rev Mol Cell Biol

953

1,069

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Nearly all aspects of RNA metabolism, from transcription and translation to mRNA decay, involve RNA helicases, which are enzymes that use ATP to bind or remodel RNA and RNA-protein complexes (ribonucleoprotein (RNP) complexes) 1 . RNA helicases are found in all three domains of life, and many viruses also encode one or more of these proteins 2,3 . Together with the structurally related DNA helicases that function in replication, recombination and repair, the RNA helicases are classified into superfamilies and families, based on sequence and structural features 3,4 . DEAD box proteins form the largest helicase family, with 37 members in humans and 26 in Saccharomyces cerevisiae 3 , and are characterized by the presence of an Asp-Glu-Ala-Asp (DEAD) motif.DEAD box helicases have central and, in many cases, essential physiological roles in cellular RNA metabolism 5 (FIG. 1). The proteins generally function as part of larger multicomponent assemblies, such as the spliceosom e or the eukaryotic translation initiation machinery 6 . Mutations and deregulation of several DEAD box proteins have been linked to disease states, including cancer 7 . Although all DEAD box proteins contain a structurally highly conserved core with conserved ATP-binding and RNA-binding sites, different proteins have been associated with diverse and seemingly unrelated functions, including the disassembly of RNPs, chaperoning during RNA folding and even stabil ization of protein complexes on RNA 5,6 . How these highly conserved proteins fulfil such an array of different functions has been a long-standing question.Research has now started to illuminate the molecular basis for this functional diversity. In this Review, we summarize how structural data, together with biochemical and biophysical studies, have revealed unexpected modes by which these proteins function. We also discuss how novel molecular and cell biological approaches have better defined the cellular roles of DEAD box helicases. We outline our current view on common structural and mechan istic themes that have emerged, and on physical models of how these 'unusual' RNA helicases work.Structures of DEAD box RNA helicases A number of structural studies have universally shown that members of the DEAD box family contain a highly conserved helicase core that harbours the binding sites for ATP and RNA 3,4,8 . The core is surrounded by variable auxiliary domains, which are thought to be critical for the diverse functions of these enzymes.Structure of the helicase core. DEAD box proteins belong to helicase superfamily 2 (SF2) 2 . Similarly to all SF2 helicases, DEAD box proteins are built around a highly conserved helicase core of two virtually identical domains that resemble the bacterial recombination protein recombinase A (RecA) 3,4,8 (FIG. 2a,b). Within this helicase core, at least 12 characteristic sequence motifs are located at conserved positions (FIG. 2a,b). Some of these motifs are conserved across the entire SF2 family, whereas others are found only in the DEAD box family 3 ....

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Section: Nuclear Specklessupporting

confidence: 91%

Section: Nuclear Specklessupporting

confidence: 91%

Section: Nuclear Specklesmentioning

confidence: 99%

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From unwinding to clamping — the DEAD box RNA helicase family

Linder

Jankowsky

2011

Nat Rev Mol Cell Biol

953

1,069

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“…A similar enhancement in activity has been reported for the eukaryotic eIF4A DEAD box helicase upon binding to its adaptor protein eIF4G, which forms part of a larger multienzyme complex involved in translation initiation (11). NMR studies have indicated that the site of interaction for eIF4G is on the C-terminal domain of eIF4A (44).…”

Section: Discussionmentioning

confidence: 56%

Allosteric Activation of the ATPase Activity of the Escherichia coli RhlB RNA Helicase

Worrall

Howe

McKay

et al. 2008

Journal of Biological Chemistry

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Helicase B (RhlB) is one of the five DEAD box RNA-dependent ATPases found in Escherichia coli. Unique among these enzymes, RhlB requires an interaction with the partner protein RNase E for appreciable ATPase and RNA unwinding activities. To explore the basis for this activating effect, we have generated a di-cistronic vector that overexpresses a complex comprising RhlB and its recognition site within RNase E, corresponding to residues 696 -762. Complex formation has been characterized by isothermal titration calorimetry, revealing an avid, enthalpyfavored interaction between the helicase and RNase E-(696 -762) with an equilibrium binding constant (K a ) of at least 1 ؋ 10 8 M ؊1 . We studied ATPase activity of mutants with substitutions within the ATP binding pocket of RhlB and on the putative interaction surface that mediates recognition of RNase E. For comparisons, corresponding mutations were prepared in two other E. coli DEAD box ATPases, RhlE and SrmB. Strikingly, substitutions at a phenylalanine near the Q-motif found in DEAD box proteins boosts the ATPase activity of RhlB in the absence of RNA, but completely inhibits it in its presence. The data support the proposal that the protein-protein and RNA-binding surfaces both communicate allosterically with the ATPase catalytic center. We conjecture that this communication may govern the mechanical power and efficiency of the helicases, and is tuned in individual helicases in accordance with cellular function.RNA helicases are a diverse set of proteins found in all three kingdoms of life that possess the ability to unwind short stretches of RNA duplexes in reactions that require the hydrolysis of nucleoside triphosphates (1). They are the largest group of enzymes in eukaryotic RNA metabolism and are involved in virtually all aspects of cellular RNA manipulation including transcription, splicing, RNA nuclear export, and ribosome biogenesis (2, 3). The DEAD box helicases are grouped in helicase superfamily 2, whose members contain nine conserved motifs, including the Walker B motif DEAD from which they take their common name (Fig. 1). Escherichia coli contains five genes encoding for DEAD box proteins; csdA (formerly called deaD), dbpA, rhlB, rhlE, and srmB (4). The gene products have a common core of 350 -400 amino acids, consisting of two domains that have the same fold found in the DNA-recombination protein RecA. Flanking this two-domain core are variable regions that are thought to be responsible for the differing properties and functions of the five helicases (4).DEAD box helicases can unwind short RNA duplexes that are no more than two helical turns in length (ϳ22 bp), and some helicases can displace avidly bound proteins from RNA (1, 5). A role of DEAD box RNA helicases as nonspecific RNA unfolding enzymes has been described (6). Yang and Jankowsky (7) have elegantly shown that DEAD box helicases use a single strand RNA region to facilitate loading onto duplex RNA where only a few base pairs are disrupted in an ATP-dependent manner, leading to destabiliza...

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“…The ATP-dependent helicase activity of recombinant or purified eIF4AI is weak; however, the RNA helicase activity of eIF4AI is stimulated by cofactors, such as eIF4B and eIF4H (43)(44)(45). Like eIF4AI, purified eIF4AIII has relatively weak helicase activity (32,45,46).…”

Section: Discussionmentioning

confidence: 99%

eIF4AIII enhances translation of nuclear cap-binding complex–bound mRNAs by promoting disruption of secondary structures in 5′UTR

Choe

Ryu

Park

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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It has long been considered that intron-containing (spliced) mRNAs are translationally more active than intronless mRNAs (identical mRNA not produced by splicing). The splicing-dependent translational enhancement is mediated, in part, by the exon junction complex (EJC). Nonetheless, the molecular mechanism by which each EJC component contributes to the translational enhancement remains unclear. Here, we demonstrate the previously unappreciated role of eukaryotic translation initiation factor 4AIII (eIF4AIII), a component of EJC, in the translation of mRNAs bound by the nuclear cap-binding complex (CBC), a heterodimer of cap-binding protein 80 (CBP80) and CBP20. eIF4AIII is recruited to the 5′-end of mRNAs bound by the CBC by direct interaction with the CBCdependent translation initiation factor (CTIF); this recruitment of eIF4AIII is independent of the presence of introns (deposited EJCs after splicing). Polysome fractionation, tethering experiments, and in vitro reconstitution experiments using recombinant proteins show that eIF4AIII promotes efficient unwinding of secondary structures in 5′UTR, and consequently enhances CBC-dependent translation in vivo and in vitro. Therefore, our data provide evidence that eIF4AIII is a specific translation initiation factor for CBC-dependent translation.eIF4AIII | cap-binding complex | translation | CTIF | nonsense-mediated mRNA decay I n mammalian cells, translation initiation is driven by two major cap-binding proteins (CBPs). One is the nuclear cap-binding complex (CBC), which is a heterodimer of nuclear CBP80 and CBP20 (CBP80/20) (1), and the other is the eukaryotic translation initiation factor (eIF) 4E, which is a major cytoplasmic CBP (2). The CBC binds the 5′-cap structure of a newly synthesized mRNA in the nucleus and then directly interacts with an eIF4G-like scaffold protein called CBP80/20-dependent translation initiation factor (CTIF) (3). Because CTIF is mostly present on the cytoplasmic side of the nuclear envelope and is found in the nucleus (3), the interaction between the CBC and CTIF may occur either in the nucleus or during mRNA export through the nuclear pore complex. In the cytoplasm, at the 5′-end of mRNA, the CBC-CTIF complex recruits the eIF3 complex (4) and then the 40S small subunit of the ribosome, thereby directing the socalled "first" (or pioneer) round of translation (1).Translation of a CBC-bound mRNA precedes that of the eIF4E-bound mRNA, because the CBC-bound mRNA is a precursor form of the eIF4E-bound mRNA (5). The timing of the replacement of the CBC by eIF4E has not yet been elucidated; however, it is known that the replacement is mediated by the action of importin α/β in a translation-independent manner (6). The replaced eIF4E at the 5′-end of mRNA recruits a scaffold protein, eIF4GI or eIF4GII, which recruits eIF3 and eIF4AI/II and, eventually, the 40S ribosomal subunit. Then, the recruited 40S subunit scans the mRNA until it reaches the authentic translation initiation codon AUG. Efficient ribosome scanning requires either eIF4AI or e...

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Modulation of the Helicase Activity of eIF4A by eIF4B, eIF4H, and eIF4F

Cited by 308 publications

References 48 publications

From unwinding to clamping — the DEAD box RNA helicase family

From unwinding to clamping — the DEAD box RNA helicase family

Allosteric Activation of the ATPase Activity of the Escherichia coli RhlB RNA Helicase

eIF4AIII enhances translation of nuclear cap-binding complex–bound mRNAs by promoting disruption of secondary structures in 5′UTR

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