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EIF5A promotes translation elongation, polysome disassembly and stress granule assembly.

ABSTRACT: Stress granules (SGs) are cytoplasmic foci at which untranslated mRNAs accumulate in cells exposed to environmental stress. We have identified ornithine decarboxylase (ODC), an enzyme required for polyamine synthesis, and eIF5A, a polyamine (hypusine)-modified translation factor, as proteins required for arsenite-induced SG assembly. Knockdown of deoxyhypusine synthase (DHS) or treatment with a deoxyhypusine synthase inhibitor (GC7) prevents hypusine modification of eIF5A as well as arsenite-induced polysome disassembly and stress granule assembly. Time-course analysis reveals that this is due to a slowing of stress-induced ribosome run-off in cells lacking hypusine-eIF5A. Whereas eIF5A only marginally affects protein synthesis under normal conditions, it is required for the rapid onset of stress-induced translational repression. Our results reveal that hypusine-eIF5A-facilitated translation elongation promotes arsenite-induced polysome disassembly and stress granule assembly in cells subjected to adverse environmental conditions.

SUBMITTER: Li CH

PROVIDER: S-EPMC2848580 | biostudies-literature | 2010 Apr

REPOSITORIES: biostudies-literature

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eIF5A promotes translation elongation, polysome disassembly and stress granule assembly.

Li Chi Ho CH Ohn Takbum T Ivanov Pavel P Tisdale Sarah S Anderson Paul P

PloS one 20100401 4

Stress granules (SGs) are cytoplasmic foci at which untranslated mRNAs accumulate in cells exposed to environmental stress. We have identified ornithine decarboxylase (ODC), an enzyme required for polyamine synthesis, and eIF5A, a polyamine (hypusine)-modified translation factor, as proteins required for arsenite-induced SG assembly. Knockdown of deoxyhypusine synthase (DHS) or treatment with a deoxyhypusine synthase inhibitor (GC7) prevents hypusine modification of eIF5A as well as arsenite-ind ...[more]

PMID: 20376341

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Project description:Translation elongation factors facilitate protein synthesis by the ribosome. Previous studies identified two universally conserved translation elongation factors, EF-Tu in bacteria (known as eEF1A in eukaryotes) and EF-G (eEF2), which deliver aminoacyl-tRNAs to the ribosome and promote ribosomal translocation, respectively. The factor eIF5A (encoded by HYP2 and ANB1 in Saccharomyces cerevisiae), the sole protein in eukaryotes and archaea to contain the unusual amino acid hypusine (N(epsilon)-(4-amino-2-hydroxybutyl)lysine), was originally identified based on its ability to stimulate the yield (endpoint) of methionyl-puromycin synthesis-a model assay for first peptide bond synthesis thought to report on certain aspects of translation initiation. Hypusine is required for eIF5A to associate with ribosomes and to stimulate methionyl-puromycin synthesis. Because eIF5A did not stimulate earlier steps of translation initiation, and depletion of eIF5A in yeast only modestly impaired protein synthesis, it was proposed that eIF5A function was limited to stimulating synthesis of the first peptide bond or that eIF5A functioned on only a subset of cellular messenger RNAs. However, the precise cellular role of eIF5A is unknown, and the protein has also been linked to mRNA decay, including the nonsense-mediated mRNA decay pathway, and to nucleocytoplasmic transport. Here we use molecular genetic and biochemical studies to show that eIF5A promotes translation elongation. Depletion or inactivation of eIF5A in the yeast S. cerevisiae resulted in the accumulation of polysomes and an increase in ribosomal transit times. Addition of recombinant eIF5A from yeast, but not a derivative lacking hypusine, enhanced the rate of tripeptide synthesis in vitro. Moreover, inactivation of eIF5A mimicked the effects of the eEF2 inhibitor sordarin, indicating that eIF5A might function together with eEF2 to promote ribosomal translocation. Because eIF5A is a structural homologue of the bacterial protein EF-P, we propose that eIF5A/EF-P is a universally conserved translation elongation factor.

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EIF5A promotes translation elongation, polysome disassembly and stress granule assembly.

Publications

eIF5A promotes translation elongation, polysome disassembly and stress granule assembly.

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