Dynamic Behavior of Arabidopsis eIF4A-III, Putative Core Protein of Exon Junction Complex: Fast Relocation to Nucleolus and Splicing Speckles under Hypoxia

Here, we identify the Arabidopsis thaliana ortholog of the mammalian DEAD box helicase, eIF4A-III, the putative anchor protein of exon junction complex (EJC) on mRNA. Arabidopsis eIF4A-III interacts with an ortholog of the core EJC component, ALY/Ref, and colocalizes with other EJC components, such...

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Published in:	The Plant cell Vol. 21; no. 5; pp. 1592 - 1606
Main Authors:	Koroleva, O.A, Calder, G, Pendle, A.F, Kim, S.H, Lewandowska, D, Simpson, C.G, Jones, I.M, Brown, J.W.S, Shaw, P.J
Format:	Journal Article
Language:	English
Published:	United States American Society of Plant Biologists 01-05-2009
Subjects:	Amino Acid Sequence Arabidopsis - drug effects Arabidopsis - metabolism Arabidopsis - ultrastructure Arabidopsis Proteins - chemistry Arabidopsis Proteins - genetics Arabidopsis Proteins - metabolism Cell culture techniques Cell Hypoxia Cell nucleolus Cell Nucleolus - metabolism Conserved Sequence Cultured cells Enzyme Inhibitors - pharmacology Eukaryotic Initiation Factor-4A - chemistry Eukaryotic Initiation Factor-4A - genetics Eukaryotic Initiation Factor-4A - metabolism Green Fluorescent Proteins - analysis Hypoxia Introns Leupeptins - pharmacology Messenger RNA Molecular Sequence Data Photobleaching Plant cells Protein Transport - drug effects Proteins Recombinant Fusion Proteins - analysis Relocation RNA Sequence Alignment Sodium Azide - pharmacology Splicing Two-Hybrid System Techniques
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Summary:	Here, we identify the Arabidopsis thaliana ortholog of the mammalian DEAD box helicase, eIF4A-III, the putative anchor protein of exon junction complex (EJC) on mRNA. Arabidopsis eIF4A-III interacts with an ortholog of the core EJC component, ALY/Ref, and colocalizes with other EJC components, such as Mago, Y14, and RNPS1, suggesting a similar function in EJC assembly to animal eIF4A-III. A green fluorescent protein (GFP)-eIF4A-III fusion protein showed localization to several subnuclear domains: to the nucleoplasm during normal growth and to the nucleolus and splicing speckles in response to hypoxia. Treatment with the respiratory inhibitor sodium azide produced an identical response to the hypoxia stress. Treatment with the proteasome inhibitor MG132 led to accumulation of GFP-eIF4A-III mainly in the nucleolus, suggesting that transition of eIF4A-III between subnuclear domains and/or accumulation in nuclear speckles is controlled by proteolysis-labile factors. As revealed by fluorescence recovery after photobleaching analysis, the nucleoplasmic fraction was highly mobile, while the speckles were the least mobile fractions, and the nucleolar fraction had an intermediate mobility. Sequestration of eIF4A-III into nuclear pools with different mobility is likely to reflect the transcriptional and mRNA processing state of the cell.
Bibliography:	Online version contains Web-only data. Address correspondence to o.koroleva@reading.ac.uk. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Peter J. Shaw (peter.shaw@bbsrc.ac.uk). www.plantcell.org/cgi/doi/10.1105/tpc.108.060434
ISSN:	1040-4651 1532-298X
DOI:	10.1105/tpc.108.060434