Versatility of the Accessory C Proteins of Sendai Virus: Contribution to Virus Assembly as an Additional Role

• DOI: 10.1128/jvi.74.12.5619-5628.2000
• Publication Date: 2002-07-27T09:55:53Z
• Authors: Mohammad K. Hasan; Atsushi Kato; Miki Muranaka; Ryoji Yamaguchi; Yuko Sakai; Ikuyoshi Hatano; Masato Tashiro; Yoshiyuki Nagai
• Keywords: 0301 basic medicine; HN Protein; Virus Assembly; Blotting, Western; Fluorescent Antibody Technique; Interferon-alpha; Interferon-beta; Phosphoproteins; Virus Replication; Respirovirus; Cell Line; 3. Good health; Viral Matrix Proteins; Viral Proteins; 03 medical and health sciences; Chlorocebus aethiops; Centrifugation, Density Gradient; Animals; RNA, Viral; Microscopy, Immunoelectron; Viral Fusion Proteins; Gene Deletion

ABSTRACT

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(−) 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-α/β. SeV C proteins thus appear to be quite versatile.