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Meriem Bekliz, Said Azza, Hervé Seligmann, Philippe Decloquement, Didier Raoult, Bernard La Scola
Acanthamoeba polyphaga mimivirus is the first giant virus ever described, with a 1.2-Mb genome which encodes 979 proteins including central components of the translation apparatus. One of these proteins, R458, was predicted to initiate translation, although its specific role remains unknown.We silenced the R458 gene using siRNA and compared viral fitness and protein expression in silenced versus wild-type mimivirus. Silencing decreased growth rate but viral particle production at the end of the viral cycle was unaffected...
March 7, 2018: Journal of Virology
P A Sakharov, S Ch Agalarov
The formation of ribosomal 48S initiation complexes at the start codon of the mRNA leader sequence that encodes obelin has been studied using the method of primer extension inhibition (toeprinting). Experiments have been performed in a system composed of purified individual components required to initiate translation. The influence of the dominant negative mutant of factor eIF4A (R362Q) on translation initiation has been studied. It has been shown that the presence of the mutant in reaction mixture has no effect on efficiency of formation of the 48S complexes at start codon of the template studied...
January 2018: Molekuliarnaia Biologiia
Esther González-Almela, Hugh Williams, Miguel A Sanz, Luis Carrasco
Animal viruses have evolved a variety of strategies to ensure the efficient translation of their mRNAs. One such strategy is the use of internal ribosome entry site (IRES) elements, which circumvent the requirement for some eukaryotic initiation factors (eIFs). Much effort has been directed to unravel the precise mechanism of translation initiation by hepatitis C virus (HCV) mRNA. In the present study, we examined the involvement of several eIFs in HCV IRES-driven translation in human cells in a comparative analysis with mRNAs bearing the encephalomyocarditis virus or the Cricket paralysis virus IRES element...
2018: Frontiers in Microbiology
Joseph A Waldron, Farheen Raza, John Le Quesne
Increased activity of the mRNA helicase eIF4A drives cellular malignancy by reprogramming cellular translation, and eIF4A activity is the direct or indirect target of many emerging cancer therapeutics. The enriched presence of (GGC)4 motifs, which have the potential to fold into two-layered G-quadruplexes, within the 5'UTRs of eIF4A-dependent mRNAs suggests that eIF4A is required for the unwinding of these structures within these eIF4A-controlled mRNAs. However, the existence of folded G-quadruplexes within cells remains controversial, and G-quadruplex folding is in direct competition with classical Watson-Crick based secondary structures...
February 19, 2018: Nucleic Acids Research
David Langlais, Regina Cencic, Neda Moradin, James M Kennedy, Kodjo Ayi, Lauren E Brown, Ian Crandall, Michael J Tarry, Martin Schmeing, Kevin C Kain, John A Porco, Jerry Pelletier, Philippe Gros
Cerebral malaria (CM) is a severe and rapidly progressing complication of infection by Plasmodium parasites that is associated with high rates of mortality and morbidity. Treatment options are currently few, and intervention with artemisinin (Art) has limited efficacy, a problem that is compounded by the emergence of resistance to Art in Plasmodium parasites. Rocaglates are a class of natural products derived from plants of the Aglaia genus that have been shown to interfere with eukaryotic initiation factor 4A (eIF4A), ultimately blocking initiation of protein synthesis...
March 6, 2018: Proceedings of the National Academy of Sciences of the United States of America
Luis Carrasco, Miguel Angel Sanz, Esther González-Almela
Sindbis virus (SINV) contains an RNA genome of positive polarity with two open reading frames (ORFs). The first ORF is translated from the genomic RNA (gRNA), rendering the viral non-structural proteins, whereas the second ORF is translated from a subgenomic mRNA (sgRNA), which directs the synthesis of viral structural proteins. SINV infection strongly inhibits host cell translation through a variety of different mechanisms, including the phosphorylation of the eukaryotic initiation factor eIF2α and the redistribution of cellular proteins from the nucleus to the cytoplasm...
February 8, 2018: Viruses
René Toribio, Irene Díaz-López, Jasminka Boskovic, Iván Ventoso
The topology and dynamics of the scanning ribosomal 43S pre-initiation complex (PIC) bound to mRNA and initiation factors (eIFs) are probably the least understood aspects of translation initiation in eukaryotes. Recently, we described a trapping mechanism in alphavirus that stalls the PIC during scanning of viral mRNA. Using this model, we were able to snapshot for the first time the eIF4A helicase bound to mRNA in a 48S initiation complex assembled in vitro. This interaction was only detected in the presence of the natural stem loop structure (DLP) located downstream from the AUG in viral mRNA that promoted stalling of the PIC, suggesting that DLP stability was enough to jam the helicase activity of eIF4A in a fraction of assembled 48S complexes...
February 5, 2018: Nucleic Acids Research
Veronica Venturi, Richard Little, Peter W Bircham, Juliana Rodigheri Brito, Paul H Atkinson, David R Maass, Paul H Teesdale-Spittle
The translation initiation machinery is emerging as an important target for therapeutic intervention, with potential in the treatment of cancer, viral infections, and muscle wasting. Amongst the targets for pharmacological control of translation initiation is the eukaryotic initiation factor 4A (eIF4A), an RNA helicase that is essential for cap-dependent translation initiation. We set out to explore the system-wide impact of a reduction of functional eIF4A. To this end, we investigated the effect of deletion of TIF1, one of the duplicate genes that produce eIF4A in yeast, through synthetic genetic array interactions and system-wide changes in GFP-tagged protein abundances...
January 31, 2018: Biochemical and Biophysical Research Communications
Daniel R Gallie
The initiation of protein synthesis requires the involvement of the eukaryotic translation initiation factor (eIF) 4G to promote assembly of the factors needed to recruit a 40S ribosomal subunit to an mRNA. Although many eukaryotes express two eIF4G isoforms that are highly similar, those in plants, referred to as eIF4G and eIFiso4G, are highly divergent in size, sequence, and domain organization. Species of the Brassicaceae and the Cleomaceae also express a divergent eIFiso4G isoform, referred to as eIFiso4G2, not found elsewhere in the plant kingdom...
2018: PloS One
Qiuxu Liu, Xiao Qi, Haidong Yan, Linkai Huang, Gang Nie, Xinquan Zhang
To select the most stable reference genes in annual ryegrass (Lolium multiflorum), we studied annual ryegrass leaf tissues exposed to various abiotic stresses by qRT-PCR and selected 11 candidate reference genes, i.e., 18S rRNA, E2, GAPDH, eIF4A, HIS3, SAMDC, TBP-1, Unigene71, Unigene77, Unigene755, and Unigene14912. We then used GeNorm, NormFinder, and BestKeeper to analyze the expression stability of these 11 genes, and used RefFinder to comprehensively rank genes according to stability. Under different stress conditions, the most suitable reference genes for studies of leaf tissues of annual ryegrass were different...
January 16, 2018: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Eden R Freire, Danielle M N Moura, Maria J R Bezerra, Camila C Xavier, Mariana C Morais-Sobral, Ajay A Vashisht, Antonio M Rezende, James A Wohlschlegel, Nancy R Sturm, Osvaldo P de Melo Neto, David A Campbell
Trypanosomatids are parasitic protozoans characterized by several unique structural and metabolic processes that include exquisite mechanisms associated with gene expression and regulation. During the initiation of protein synthesis, for instance, mRNA selection for translation seems to be mediated by different eIF4F-like complexes, which may play a significant role in parasite adaptation to different hosts. In eukaryotes, the heterotrimeric eIF4F complex (formed by eIF4E, eIF4G, and eIF4A) mediates mRNA recognition and ribosome binding and participates in various translation regulatory events...
December 29, 2017: Current Genetics
Christin Müller, Falk W Schulte, Kerstin Lange-Grünweller, Wiebke Obermann, Ramakanth Madhugiri, Stephan Pleschka, John Ziebuhr, Roland K Hartmann, Arnold Grünweller
Coronaviruses (CoV) and picornaviruses are plus-strand RNA viruses that use 5' cap-dependent and cap-independent strategies, respectively, for viral mRNA translation initiation. Here, we analyzed the effects of the plant compound silvestrol, a specific inhibitor of the DEAD-box RNA helicase eIF4A, on viral translation using a dual luciferase assay and virus-infected primary cells. Silvestrol was recently shown to have potent antiviral activity in Ebola virus-infected human macrophages. We found that silvestrol is also a potent inhibitor of cap-dependent viral mRNA translation in CoV-infected human embryonic lung fibroblast (MRC-5) cells...
December 16, 2017: Antiviral Research
Patrick D Slaine, Mariel Kleer, Nathan K Smith, Denys A Khaperskyy, Craig McCormick
Eukaryotic translation initiation factor 4A (eIF4A) is a helicase that facilitates assembly of the translation preinitiation complex by unwinding structured mRNA 5' untranslated regions. Pateamine A (PatA) and silvestrol are natural products that disrupt eIF4A function and arrest translation, thereby triggering the formation of cytoplasmic aggregates of stalled preinitiation complexes known as stress granules (SGs). Here we examined the effects of eIF4A inhibition by PatA and silvestrol on influenza A virus (IAV) protein synthesis and replication in cell culture...
December 18, 2017: Viruses
Katelyn M Green, M Rebecca Glineburg, Michael G Kearse, Brittany N Flores, Alexander E Linsalata, Stephen J Fedak, Aaron C Goldstrohm, Sami J Barmada, Peter K Todd
Repeat-associated non-AUG (RAN) translation allows for unconventional initiation at disease-causing repeat expansions. As RAN translation contributes to pathogenesis in multiple neurodegenerative disorders, determining its mechanistic underpinnings may inform therapeutic development. Here we analyze RAN translation at G4 C2 repeat expansions that cause C9orf72-associated amyotrophic lateral sclerosis and frontotemporal dementia (C9RAN) and at CGG repeats that cause fragile X-associated tremor/ataxia syndrome...
December 8, 2017: Nature Communications
Paul Yourik, Colin Echeverría Aitken, Fujun Zhou, Neha Gupta, Alan G Hinnebusch, Jon R Lorsch
eIF4A is a DEAD-box RNA-dependent ATPase thought to unwind RNA secondary structure in the 5'-untranslated regions (UTRs) of mRNAs to promote their recruitment to the eukaryotic translation pre-initiation complex (PIC). We show that eIF4A's ATPase activity is markedly stimulated in the presence of the PIC, independently of eIF4E•eIF4G, but dependent on subunits i and g of the heteromeric eIF3 complex. Surprisingly, eIF4A accelerated the rate of recruitment of all mRNAs tested, regardless of their degree of structural complexity...
November 30, 2017: ELife
Eden R Freire, Nancy R Sturm, David A Campbell, Osvaldo P de Melo Neto
Trypanosomatid protozoa are unusual eukaryotes that are well known for having unusual ways of controlling their gene expression. The lack of a refined mode of transcriptional control in these organisms is compensated by several post-transcriptional control mechanisms, such as control of mRNA turnover and selection of mRNA for translation, that may modulate protein synthesis in response to several environmental conditions found in different hosts. In other eukaryotes, selection of mRNA for translation is mediated by the complex eIF4F, a heterotrimeric protein complex composed by the subunits eIF4E, eIF4G, and eIF4A, where the eIF4E binds to the 5'-cap structure of mature mRNAs...
October 27, 2017: Pathogens
Shu-Mei Dong, Ji-Hui Cui, Wei Zhang, Xue-Wen Zhang, Tian-Chao Kou, Qiu-Chen Cai, Sha Xu, Shan You, Dong-Shuai Yu, Lei Ding, Jian-Hua Lai, Ming Li, Kai-Jun Luo
Apoptotic hemocytes induced by Microplitis bicoloratus parasitism have been reported, and M. bicoloratus bracovirus (MbBV) is known to be the apoptosis inducer. However, the mechanism how MbBV regulates apoptosis remains unclear. eIF4A, one of translation initiation factors, was found from a Spodoptera litura transcriptome, the expression of which in the parasitized hemocytes of S. litura was inhibited in RT-qPCR analysis. The western blot also illustrated eIF4A at 6-day post-parasitization was inhibited in hemocytes...
November 2017: Archives of Insect Biochemistry and Physiology
E A Sogorin, G K Selikhanov, S Ch Agalarov
Recently we described a novel phenomenon observed during eukaryotic translation in a cell-free system: the coupling of initiation and termination on different mRNA molecules. Here we show that the phenomenon does not depend on a special mode of initiation. The mRNAs with certain leader sequences known to require different determinants for successful initiation were examined. Even in a case of using the intergenic internal ribosome entry site (IRES) of cricket paralysis virus RNA as the leader sequence, while no initiation factors are required, the effect of coupling is well expressed, including trials in the presence of hippuristanol as an inhibitor of eIF4A...
July 2017: Biochemistry. Biokhimii︠a︡
Polina N Vikhreva, Svetlana V Kalinichenko, Igor V Korobko
Programmed cell death 4 (Pdcd4) is frequently suppressed in tumors of various origins and its suppression correlates with tumor progression. Pdcd4 inhibits cap-dependent translation from mRNAs with highly structured 5'-regions through interaction with the eukaryotic translation initiation factor 4A (eIF4A) helicase and a target transcript. Decrease in Pdcd4 protein is believed to provide a relief of otherwise suppressed eIF4A-dependent translation of proteins facilitating tumor progression. However, it remains unknown if lowered Pdcd4 levels in cells suffices to cause a relief in translation inhibition through appearance of the Pdcd4-free translation-competent eIF4A protein, or more complex and selective mechanisms are involved...
October 2, 2017: Cell Cycle
Brian C Avanzino, Gabriele Fuchs, Christopher S Fraser
Picornaviruses use internal ribosome entry sites (IRESs) to translate their genomes into protein. A typical feature of these IRESs is their ability to bind directly to the eukaryotic initiation factor (eIF) 4G component of the eIF4F cap-binding complex. Remarkably, the hepatitis A virus (HAV) IRES requires eIF4E for its translation, but no mechanism has been proposed to explain this. Here we demonstrate that eIF4E regulates HAV IRES-mediated translation by two distinct mechanisms. First, eIF4E binding to eIF4G generates a high-affinity binding conformation of the eIF4F complex for the IRES...
September 5, 2017: Proceedings of the National Academy of Sciences of the United States of America
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