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      HIV-1 Rev protein specifies the viral RNA export pathway by suppressing TAP/NXF1 recruitment

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          Abstract

          Nuclear RNA export pathways in eukaryotes are often linked to the fate of a given RNA. Therefore, the choice of export pathway should be well-controlled to avoid an unfavorable effect on gene expression. Although some RNAs could be exported by more than one pathway, little is known about how the choice is regulated. This issue is highlighted when the human immunodeficiency virus type 1 (HIV-1) Rev protein induces the export of singly spliced and unspliced HIV-1 transcripts. How these RNAs are exported is not well understood because such transcripts should have the possibility of utilizing CRM1-dependent export via Rev or cellular TAP/NXF1-dependent export via the transcription/export (TREX) complex, or both. Here we found that Rev suppressed TAP/NXF1-dependent export of model RNA substrates that recapitulated viral transcripts. In this effect, Rev interacted with the cap-binding complex and inhibited the recruitment of the TREX complex. Thus, Rev controls the identity of the factor occupying the cap-proximal region that determines the RNA export pathway. This ribonucleoprotein remodeling activity of Rev may favor viral gene expression.

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          Exporting RNA from the nucleus to the cytoplasm.

          The transport of RNA molecules from the nucleus to the cytoplasm is fundamental for gene expression. The different RNA species that are produced in the nucleus are exported through the nuclear pore complexes via mobile export receptors. Small RNAs (such as tRNAs and microRNAs) follow relatively simple export routes by binding directly to export receptors. Large RNAs (such as ribosomal RNAs and mRNAs) assemble into complicated ribonucleoprotein (RNP) particles and recruit their exporters via class-specific adaptor proteins. Export of mRNAs is unique as it is extensively coupled to transcription (in yeast) and splicing (in metazoa). Understanding the mechanisms that connect RNP formation with export is a major challenge in the field.
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            The HIV-1 Rev activation domain is a nuclear export signal that accesses an export pathway used by specific cellular RNAs.

            HIV-1 Rev protein directs nuclear export of pre-mRNAs and mRNAs containing its binding site, the Rev response element (RRE). To define how Rev acts, we used conjugates between bovine serum albumin (BSA) and peptides comprising the Rev activation domain (BSA-R). BSA-R inhibited Rev-mediated nuclear RNA export, whereas a mutant activation domain peptide conjugate did not. BSA-R did not affect the export of mRNA, tRNA, or ribosomal subunits, but did inhibit export of 5S rRNA and spliceosomal U snRNAs. BSA-R was itself exported from the nucleus in an active, saturable manner. Thus, the Rev activation domain constitutes a nuclear export signal that redirects RRE-containing viral RNAs to a non-mRNA export pathway.
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              SR splicing factors serve as adapter proteins for TAP-dependent mRNA export.

              The only mammalian RNA binding adapter proteins known to partner with TAP/NXF1, the primary receptor for general mRNA export, are members of the REF family. We demonstrate that at least three shuttling SR (serine/arginine-rich) proteins interact with the same domain of TAP/NXF1 that binds REFs. Included are 9G8 and SRp20, previously shown to promote the export of intronless RNAs. A peptide derived from the N terminus of 9G8 inhibits the binding of both REF and SR proteins to TAP/NXF1 in vitro, and this finding argues for competitive interactions. In Xenopus oocytes, the N terminus of 9G8 exhibits a dominant-negative effect on mRNA export from the nucleus, while addition of excess TAP/NXF1 overcomes this inhibition. Thus, multiple adapters including SR proteins most likely cooperate to recruit multiple copies of TAP/NXF1 for efficient mRNA export.
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                Author and article information

                Journal
                Nucleic Acids Res
                Nucleic Acids Res
                nar
                nar
                Nucleic Acids Research
                Oxford University Press
                0305-1048
                1362-4962
                01 June 2014
                20 April 2014
                20 April 2014
                : 42
                : 10
                : 6645-6658
                Affiliations
                Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan
                Author notes
                [* ]To whom correspondence should be addressed. Tel: +81 75 751 4018; Fax: +81 75 751 3992; Email: hitoohno@ 123456virus.kyoto-u.ac.jp
                Correspondence may also be addressed to Ichiro Taniguchi. Tel: +81 75 751 3993; Fax: +81 75 751 3992; Email: itaniguc@ 123456virus.kyoto-u.ac.jp
                Article
                10.1093/nar/gku304
                4041468
                24753416
                08ce646d-cfd8-4e67-93aa-133b1bee422a
                © The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/3.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited

                History
                : 31 March 2014
                : 31 March 2014
                : 20 November 2013
                Page count
                Pages: 14
                Categories
                RNA
                Custom metadata
                2014

                Genetics
                Genetics

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