The messenger RNAs of SV5 and two strains of Sendai virus were isolated from infected cells and translated in a wheat germ cell-free system. Comparison of the peptide maps of the polypeptides synthesizedin vivo andin vitro established that the nonglycosylated polypeptides P, NP, and M of both SV5 and Sendai virus had been synthesizedin vitro. In immunoprecipitation studies of the putative SV5 polypeptides synthesizedin vitro, antiserum against whole virions precipitated NP, P, and M, and other polypeptides which did not comigrate with mature virion polypeptides. Monospecific antisera against the HN and F glycoproteins precipitated two of the latter polypeptides with molecular weights of ∼55,000 and 50,000, respectively, suggesting that the nonglycosylated forms of these polypeptides had been synthesizedin vitro. Polypeptide C, previously found in Sendai virus-infected cells and proposed to be a virus-specific nonstructural polypeptide, has been found to exhibit strain-specific differences in migration in polyacrylamide gels. Polypeptides with the appropriate strain-specific migration have been synthesizedin vitro with mRNAs from cells infected with the different Sendai virus strains, and shown by peptide mapping to be the same polypeptides as those synthesizedin vivo. The results have thus provided further evidence that C is a virus-coded nonstructural protein. Another polypeptide (C′), with migrates slightly slower than C, has been found in infected cells and synthesizedin vitro. This polypeptide also exhibits strain-specific differences in migration in polyacrylamide gel electrophoresis, and has been shown by peptide mapping to be similar to C. The explanation for the difference in migration between C and C′ is as yet unknown.
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