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Published March 1985 | public
Journal Article

The nonstructural proteins of Sindbis virus as studied with an antibody specific for the C terminus of the nonstructural readthrough polyprotein


A dodecapeptide containing the sequence of the C terminus of the nonstructural polyprotein of Sindbis virus has been synthesized and used to immunize rabbits. The antisera obtained precipitated polypeptides from cells infected with the HR strain of Sindbis or with temperature-sensitive mutants tsll or tsl8. Four different polypeptides, having apparent molecular weights of approximately 250,000, 220,000, 155,000, and 72,000, were immunoprecipitated by the antipeptide antiserum. The largest of these polypeptides is sufficiently large to represent a polyprotein translated from the entire nonstructural region of the genome. These data suggest that nsP4 of molecular weight 72,000 is produced by translation of the entire nonstructural region of the genome, which requires readthrough of an opal termination codon immediately upstream of nsP4, followed by post-translational cleavage of this polyprotein. The amounts of nsP4 and its precursors found in infected cells are small relative to the amounts of other nonstructural proteins present, as would be expected if readthrough of a termination codon is required. In addition, the relative amounts of nsP4 and of its precursors differ in HR-infected or ts mutant-infected cells and differ with temperature of infection, suggesting that temperature of infection or ts lesions affect translation and processing of the precursor polyprotein.

Additional Information

© 1985 Academic Press, Inc. Received August 17, 1984; accepted October 30, 1984. We are grateful to E. Lenches for expert technical assistance, to T. Hunkapiller for computer programs used in construction of the figures, to L. Hood for use of computer facilities, and to J. Shively for HF hydrolysis of peptide C. This work was supported by Grants GM06965, AI10793, and AI20612 from NIH and Grant PCM8316856 from NSF. S. L. was supported by a fellowship from the Universidad Nacíonal Autónoma de México.

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