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Journal of Virology, June 2000, p. 5619-5628, Vol. 74, No. 12
Department of Viral Diseases and Vaccine
Control,1 Department of Safety Research
on Biologics,4 and AIDS Research
Center,5 National Institute of Infectious
Diseases, Tokyo 208-0011, Department of Pathology, Faculty of
Agriculture, Miyazaki University, Miyazaki
889-2155,2 and Department of Viral
Infection, Institute of Medical Science, University of Tokyo, Tokyo
108-8639,3 Japan
Received 29 December 1999/Accepted 23 March 2000
The P/C mRNA of Sendai virus (SeV) encodes a nested set
of accessory proteins, C', C, Y1, and Y2, referred to collectively as C
proteins, using the +1 frame relative to the open reading frame of
phospho (P) protein and initiation codons at different positions. The C
proteins appear to be basically nonstructural proteins as they are
found abundantly in infected cells but greatly underrepresented in the
virions. We previously created a 4C(
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Versatility of the Accessory C Proteins of Sendai Virus:
Contribution to Virus Assembly as an Additional Role
) SeV, which expresses none of
the four C proteins, and concluded that the C proteins are
categorically nonessential gene products but greatly contribute to
viral full replication and infectivity (A. Kurotani et al., Genes Cells
3:111-124, 1998). Here, we further characterized the 4C() virus
multiplication in cultured cells. The viral protein and mRNA synthesis
was enhanced with the mutant virus relative to the parental wild-type
(WT) SeV. However, the viral yields were greatly reduced. In addition,
the 4C() virions appeared to be highly anomalous in size, shape, and
sedimentation profile in a sucrose gradient and exhibited the ratios of
infectivity to hemagglutination units significantly lower than those of
the WT. In the WT infected cells, C proteins appeared to
colocalize almost perfectly with the matrix (M) proteins, pretty well
with an external envelope glycoprotein
(hemagglutinin-neuraminidase [HN]), and very poorly with the internal
P protein. In the absence of C proteins, there was a significant delay
of the incorporation of M protein and both of the envelope proteins, HN
and fusion (F) proteins, into progeny virions. These results strongly
suggest that the accessory and basically nonstructural C proteins are critically required in the SeV assembly process. This role of C
proteins was further found to be independent of their recently discovered function to counteract the antiviral action of
interferon-
/
. SeV C proteins thus appear to be quite versatile.
*
Corresponding author. Mailing address: AIDS Research
Center, National Institute of Infectious Diseases, Toyama 1-23-1, Shinjuku-ku, Tokyo 162-8640, Japan. Phone: 81 3 5285-1111, ext. 2302. Fax: 81 3 5285-1165. E-mail: ynagai{at}nih.go.jp.
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