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Journal of Virology, April 2001, p. 3404-3412, Vol. 75, No. 7
Department of Virology, Research Institute
for Microbial Diseases, Osaka University, Suita, Osaka 565-0871, Japan
Received 5 September 2000/Accepted 3 January 2001
Nuclear transport of viral nucleic acids is crucial to the life
cycle of many viruses. Borna disease virus (BDV) belongs to the order
Mononegavirales and replicates its RNA genome in the nucleus. Previous studies have suggested that BDV nucleoprotein (N) and
phosphoprotein (P) have important functions in the nuclear import of
the viral ribonucleoprotein (RNP) complexes via their nuclear targeting
activity. Here, we showed that BDV N has cytoplasmic localization
activity, which is mediated by a nuclear export signal (NES) within the
sequence. Our analysis using deletion and substitution mutants of N
revealed that NES of BDV N consists of a canonical leucine-rich motif
and that the nuclear export activity of the protein is mediated through
the chromosome region maintenance protein-dependent pathway.
Interspecies heterokaryon assay indicated that BDV N shuttles between
the nucleus and cytoplasm as a nucleocytoplasmic shuttling protein.
Furthermore, interestingly, the NES region overlaps a binding site to
the BDV P protein, and nuclear export of a 38-kDa form of BDV N is
prevented by coexpression of P. These results suggested that BDV N has
two contrary activities, nuclear localization and export activity, and
plays a critical role in the nucleocytoplasmic transport of BDV RNP by
interaction with other viral proteins.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.7.3404-3412.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Borna Disease Virus Nucleoprotein Requires both
Nuclear Localization and Export Activities for Viral
Nucleocytoplasmic Shuttling
*
Corresponding author. Mailing address: Department of
Virology, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan. Phone: 81-6-6879-8308. Fax: 81-6-6879-8310. E-mail:
tomonaga{at}biken.osaka-u.ac.jp.
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