The Scanning Mechanism of Eukaryotic Translation Initiation

Hinnebusch, Alan G.

doi:10.1146/annurev-biochem-060713-035802

Cited by 699 publications

(841 citation statements)

References 240 publications

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“…To obtain a fuller appreciation of where eIF4F fits into the grand scheme of things, the reader may find one or more of the closing references to reviews useful (72)(73)(74)(75)(76)(77)(78)(79)(80)(81)(82)(83)(84)(85) …”

Section: Other Complicationsmentioning

confidence: 99%

eIF4F: A Retrospective

Merrick

2015

Journal of Biological Chemistry

145

156

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The original purification of the heterotrimeric eIF4F was published over 30 years ago (Grifo, J. A., Tahara, S. M., Morgan, M. A., Shatkin, A. J., and Merrick, W. C. (1983) J. Biol. Chem. 258, 5804 -5810). Since that time, numerous studies have been performed with the three proteins specifically required for the translation initiation of natural mRNAs, eIF4A, eIF4B, and eIF4F. These have involved enzymatic and structural studies of the proteins and a number of site-directed mutagenesis studies. The regulation of translation exhibited through the mammalian target of rapamycin (mTOR) pathway is predominately seen as the phosphorylation of 4E-BP, an inhibitor of protein synthesis that functions by binding to the cap binding subunit of eIF4F (eIF4E). A hypothesis that requires the disassembly of eIF4F during translation initiation to yield free subunits (eIF4A, eIF4E, and eIF4G) is presented. The Biology of eIF4FThe initial findings in the study of natural mRNA translation reflected the newly discovered m 7 G cap at the 5Ј end of eukaryotic mRNAs (2). mRNAs lacking this structure were translated with less efficiency than mRNAs that contained this structure (3). This unique structure allowed for specific assays or purifications, many established in the laboratory of Dr. Aaron Shatkin with assists from his colleagues. Two of note were the use of m 7 G-Sepharose for affinity purification (4, 5) and the crosslinking of periodate-oxidized mRNAs to proteins (6).The initial application of these methodologies identified two different molecular weight species (about 25,000 and at least 200,000), although the high molecular weight protein contained the small molecular weight component, now known as eIF4E (7). Given the size of several other known translation factors, the question was whether these contained the small molecular weight subunit (notably eIF3 and eIF4B) (8 -11). Ultimate purification of eIF4F indicated that neither of these were correct but that eIF4F would form stable complexes with either, thus being consistent with the eIF4E component tracking with them. At the same time, it was recognized that the 46,000 molecular weight subunit of eIF4F was eIF4A. By physical analysis, eIF4F was a heterotrimeric complex of eIF4A, eIF4E, and eIF4G (1).The next studies were to attempt to identify the functions of the various proteins required specifically for natural mRNA translation (eIF4A, eIF4B, and eIF4F). The characteristics of these three proteins were very different. In the absence of ATP, binding to RNA could only be well demonstrated with eIF4F (Table 1). eIF4A and eIF4F could hydrolyze ATP in the presence of single-stranded RNA, and eIF4B would enhance both of these activities (12). In terms of mechanism, the coupling of the binding of ATP and RNA was realized in recognizing that eIF4A or eIF4F had the ability to unwind duplex RNA. As noted in Table 1, the "strength" of the helicase activity was greater with eIF4F (14).As the ability to determine amino acid sequence from RNA sequence advanced, it was found that there...

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Section: Other Complicationsmentioning

confidence: 99%

eIF4F: A Retrospective

Merrick

2015

Journal of Biological Chemistry

145

156

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“…28,63,64 It also plays a role, along with eIF5B, in ensuring proper subunit joining and formation of elongation-competent 80S ribosomes. 28,63,64 Hydroxyl radical probing and structural modeling involving eIF1A and Tetrahymena thermophila 40S ribosomal subunits (based on bacterial 30S:IF1 complex information) at »3.9A suggested that eIF1A resides near the A-site and makes contacts with eukaryotespecific proteins eS27 and eS30 as well as conserved protein uS12 which harbors eukaryote-specific extensions. 15,65 However, direct involvement of uS12 eukaryote-specific extensions in eIF1A binding has not been proven yet.…”

Section: E999576-6mentioning

confidence: 99%

“…The 'open' scanningcompetent conformation of the 40S subunit allows sampling of non-AUG triplets during movement of the initiation complex, but does not lead to efficient codon-anticodon base pairing. 27,28 During scanning, eIF1 acts as a gatekeeper and blocks the release of Pi from partially hydrolyzed eIF2 GTP into eIF2 GDP Pi induced by eIF5 and maintains the 'open' 40S conformation. Upon recognition of a start AUG codon, factors are rearranged and eIF1 is released.…”

Section: Introductionmentioning

confidence: 99%

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Eukaryote-specific extensions in ribosomal proteins of the small subunit: Structure and function

Ghosh

Komar

2015

Translation

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Keywords: conserved ribosomal proteins, eukaryotic/yeast ribosome, eukaryote-specific extensions, eukaryotic translation initiation factors, protein synthesis, small ribosomal subunitHigh-resolution structures of yeast ribosomes have improved our understanding of the architecture and organization of eukaryotic rRNA and proteins, as well as eukaryote-specific extensions present in some conserved ribosomal proteins. Despite this progress, assignment of specific functions to individual proteins and/or eukaryotespecific protein extensions remains challenging. It has been suggested that eukaryote-specific extensions of conserved proteins from the small ribosomal subunit may facilitate eukaryote-specific reactions in the initiation phase of protein synthesis. This review summarizes emerging data describing the structural and functional significance of eukaryotespecific extensions of conserved small ribosomal subunit proteins, particularly their possible roles in recruitment and spatial organization of eukaryote-specific initiation factors.

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“…A key mechanism in the regulation of translation initiation is phosphorylation of serine 51 of the ␣ subunit of eIF2 (eIF2␣-P) (1). During translation initiation, eIF2 combines with initiator Met-tRNA i Met , GTP, and the 40S ribosomal subunit and, when associated with the eIF4 proteins on the mRNA, forms the 48S complex that facilitates start codon selection.…”

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confidence: 99%

Ribosome Elongation Stall Directs Gene-specific Translation in the Integrated Stress Response

Young

Palam

et al. 2016

Journal of Biological Chemistry

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Upon exposure to environmental stress, phosphorylation of the ␣ subunit of eIF2 (eIF2␣-P) represses global protein synthesis, coincident with preferential translation of gene transcripts that mitigate stress damage or alternatively trigger apoptosis. Because there are multiple mammalian eIF2 kinases, each responding to different stress arrangements, this translational control scheme is referred to as the integrated stress response (ISR). Included among the preferentially translated mRNAs induced by eIF2␣-P is that encoding the transcription factor CHOP (DDIT3/GADD153). Enhanced levels of CHOP promote cell death when ISR signaling is insufficient to restore cell homeostasis. Preferential translation of CHOP mRNA occurs by a mechanism involving ribosome bypass of an inhibitory upstream ORF (uORF) situated in the 5-leader of the CHOP mRNA. In this study, we used biochemical and genetic approaches to define the inhibitory features of the CHOP uORF and the biological consequences of loss of the CHOP uORF on CHOP expression during stress. We discovered that specific sequences within the CHOP uORF serve to stall elongating ribosomes and prevent ribosome reinitiation at the downstream CHOP coding sequence. As a consequence, deletion of the CHOP uORF substantially increases the levels and modifies the pattern of induction of CHOP expression in the ISR. Enhanced CHOP expression leads to increased expression of key CHOP target genes, culminating in increased cell death in response to stress.

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The Scanning Mechanism of Eukaryotic Translation Initiation

Cited by 699 publications

References 240 publications

eIF4F: A Retrospective

eIF4F: A Retrospective

Eukaryote-specific extensions in ribosomal proteins of the small subunit: Structure and function

Ribosome Elongation Stall Directs Gene-specific Translation in the Integrated Stress Response

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