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Journal of Virology, March 1999, p. 2222-2231, Vol. 73, No. 3
Division of Virology,
Received 16 September 1998/Accepted 1 December 1998
The influenza virus genome is transcribed in the nuclei of infected
cells but assembled into progeny virions in the cytoplasm. This is
reflected in the cellular distribution of the virus nucleoprotein (NP),
a protein which encapsidates genomic RNA to form ribonucleoprotein structures. At early times postinfection NP is found in the nucleus, but at later times it is found predominantly in the cytoplasm. NP
contains several sequences proposed to act as nuclear localization signals (NLSs), and it is not clear how these are overridden to allow
cytoplasmic accumulation of the protein. We find that NP binds tightly
to filamentous actin in vitro and have identified a cluster of residues
in NP essential for the interaction. Complexes containing RNA, NP, and
actin could be formed, suggesting that viral ribonucleoproteins also
bind actin. In cells, exogenously expressed NP when expressed at a high
level partitioned to the cytoplasm, where it associated with F-actin
stress fibers. In contrast, mutants unable to bind F-actin efficiently
were imported into the nucleus even under conditions of high-level
expression. Similarly, nuclear import of NLS-deficient NP molecules was
restored by concomitant disruption of F-actin binding. We propose that the interaction of NP with F-actin causes the cytoplasmic retention of
influenza virus ribonucleoproteins.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Modulation of Nuclear Localization of the Influenza
Virus Nucleoprotein through Interaction with Actin Filaments
*
Corresponding author. Mailing address: Division of
Virology, Department of Pathology, University of Cambridge, Tennis
Court Rd., Cambridge CB2 1QP, United Kingdom. Phone: 44 1223 336921. Fax: 44 1223 336926. E-mail:
pd1{at}mole.bio.cam.ac.uk.
Journal of Virology, March 1999, p. 2222-2231, Vol. 73, No. 3
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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