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J. Virol., 07 1997, 5133-5139, Vol 71, No. 7
JM Pyper and AE Gartner
Borna disease virus (BDV) is a nonsegmented negative-strand (NNS) RNA virus
that is unusual because it replicates in the nucleus. The most abundant
viral protein in infected cells is a 38/39-kDa doublet that is presumed to
represent the nucleocapsid. Infectious particles also contain high levels
of this protein, accounting for at least 50% of the viral proteins. The two
forms of the protein differ by an additional 13 amino acids that are
present at the amino terminus of the 39-kDa form and missing from the
38-kDa form. To examine whether this difference in amino acid content
affects the localization of this protein in cells, the 39- and 38-kDa
proteins were expressed in transfected cells. The 39- kDa form was
concentrated in the nucleus, whereas the 38-kDa form was found in both the
nucleus and cytoplasm. Inspection of the extra 13 amino acids present in
the 39-kDa form revealed a sequence (Pro-Lys-Arg- Arg) that is very similar
to the nuclear localization signals (in both sequence homology and
amino-terminal location) of the VP1 proteins of simian virus 40 and
polyomavirus. Primer extension analysis of total RNA from infected cells
suggests that there are two mRNA species encoding the two forms of the
nucleocapsid protein. In infected cells, the 39-kDa form is expressed at
about twofold-higher levels than the 38- kDa form at both the RNA and
protein levels. The novel nuclear localization of the 39-kDa
nucleocapsid-like protein suggests that this form of the protein is
targeted to the nucleus, the site for viral RNA replication, and that it
may associate with genomic RNA.
Copyright © 1997, American Society for Microbiology
Molecular basis for the differential subcellular localization of the 38- and 39-kilodalton structural proteins of Borna disease virus
Department of Comparative Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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