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Journal of Virology, January 2001, p. 408-419, Vol. 75, No. 1
Division of Virology, Department of
Pathology, University of Cambridge, Cambridge CB2
1QP,1 and Institute for Animal
Health, Compton, Newbury, Berks RG20 7NN,2
United Kingdom
Received 10 July 2000/Accepted 10 October 2000
Influenza virus transcription occurs in the nuclei of infected
cells, where the viral genomic RNAs are complexed with a
nucleoprotein (NP) to form ribonucleoprotein (RNP) structures. Prior to
assembly into progeny virions, these RNPs exit the nucleus and
accumulate in the cytoplasm. The mechanisms responsible for RNP export
are only partially understood but have been proposed to involve the viral M1 and NS2 polypeptides. We found that the drug leptomycin B
(LMB), which specifically inactivates the cellular CRM1 polypeptide, caused nuclear retention of NP in virus-infected cells, indicating a
role for the CRM1 nuclear export pathway in RNP egress. However, no
alteration was seen in the cellular distribution of M1 or NS2, even in
the case of a mutant virus which synthesizes greatly reduced amounts of
NS2. Furthermore, NP was distributed throughout the nuclei of
infected cells at early times postinfection but, when retained in the
nucleus at late times by LMB treatment, was
redistributed to the periphery of the nucleoplasm. No such change was
seen in the nuclear distribution of M1 or NS2 after drug
treatment. Similar to the behavior of NP, M1 and NS2 in infected cells,
LMB treatment of cells expressing each polypeptide in isolation caused
nuclear retention of NP but not M1 or NS2. Conversely, overexpression of CRM1 caused increased cytoplasmic accumulation of NP but had little
effect on M1 or NS2 distribution. Consistent with this, NP bound CRM1
in vitro. Overall, these data raise the possibility that RNP export is
mediated by a direct interaction between NP and the cellular CRM1
export pathway.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.1.408-419.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Interaction of the Influenza Virus Nucleoprotein
with the Cellular CRM1-Mediated Nuclear Export Pathway
*
Corresponding author. Mailing address: Division of
Virology, Department of Pathology, University of Cambridge, Tennis
Court Rd., Cambridge CB2 1QP, United Kingdom. Phone: 44 1223 336918. Fax: 44 1223 336926. E-mail:
pd1{at}mole.bio.cam.ac.uk.
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