Identification of an Additional Sendai Virus Non-structural Protein Encoded by the P/C mRNA

Abstract

SUMMARYPeptide antiserum and monoclonal antibodies have detected a previously unrecognized small non-structural protein in Sendai virus-infected cells. This protein, designated X, appears to represent the C-terminal 95 amino acids of the P protein reading frame. The X protein appears to be almost as abundant as the P protein on a molar basis in vivo. No evidence of a precursor-product relationship between the X and P proteins could be found.Sendai virus, a member of the parainfluenza virus genus of the paramyxovirus family, encodes its entire genetic information within a non-segmented 15 kb negative strand (-) RNA genome (Kingsbury, 1974;Kolakofsky et al., 1974). Upon infection, this genetic information is expressed via positive-sense mRNAs transcribed from the-genome by the virion-associated polymerase. These transcripts are largely monocistronic, encoding the NP, M, F, HN and L proteins. The P mRNA, however, has been demonstrated to be polycistronic. In addition to encoding the 568 amino acid (aa) P protein, it also codes for a pair of non-structural proteins, C (204 aa) and C' (181 aa) (Curran et al., 1986;Dethlefsen & Kolakofsky, 1983;Giorgi et al., 1983) which represent a C-coterminal nested set and are derived from an overlapping open reading frame (ORF) (see Fig. 1). The C overlapping ORF has also been conserved in the closely related human parainfluenza virus 3 (Spriggs & Collins, 1986a) as well as the two morbilliviruses examined to date, measles virus and canine distemper virus (Barrett et al., 1985;Bellini et al., 1985). Curiously, in the case of the parainfluenza viruses simian virus 5, Newcastle disease virus and mumps virus, non-structural proteins are again encoded within the P mRNA, but here these non-structural proteins appear to share tryptic peptides with the P protein and are therefore thought to be encoded by the same ORF (Collins et al., 1982;Herrler & Compans, 1982;Paterson et al., 1984). Only in the case of respiratory syncytial virus, a member of the more distinctly related pneumovirus genus, is the P mRNA thought to be monocistronic (Collins et al., 1984).Recently, Herman (1986) has found that the NS mRNA of the rhabdovirus vesicular stomatitis virus (VSV), which is thought to be the VSV equivalent of the parainfluenza virus P mRNA, also codes for a second small protein, representing the C-terminal 62 aa of the 265 aa long NS protein. Since the Sendal virus P protein and the VSV NS protein have several characteristics in common, and antiserum specific for the C-terminal t6 aa of the Sendai virus P protein is available, we examined whether the same also applies to Sendai virus.Sendai virus (Harris strain)-infected BHK cells were labelled for 2 h at 18 h post-infection, when marked cytopathic effects are apparent, as well as a parallel uninfected culture. Under these conditions, host protein synthesis has largely been displaced by the viral protein synthesis and the virus structural proteins and the non-structural C protein can clearly be detected above the remaining cellular background ...

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A New Ebola Virus Nonstructural Glycoprotein Expressed through RNA Editing

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