Control of vesicular stomatitis virus protein synthesis

Abstract

The five structural polypeptides of vesicular stomatitis virus are synthesized in infected cells at nonequimolar rates which correspond to their relative amounts in the virus particle. These experiments are concerned with the mechanism(s) responsible for the relative rates of viral polypeptide synthesis. Treatment of infected cells with amino acid analogs in order to prevent formation of functional viral proteins resulted in inhibition of viral genome replication and virion assembly. This treatment, however, did not alter the relative rates of viral polypeptide synthesis. This suggested that the mechanisms determining these rates do not require the function of newly-synthesized viral proteins and do not involve direct coupling between protein synthesis and virion assembly. Relative translation frequencies of viral messenger RNA molecules coding for each polypeptide were compared by treating cells with low levels of cycloheximide and anisomycin, inhibitors of protein synthesis that interfere preferentially with polypeptide chain elongation. Under these conditions the rate of synthesis of each viral polypeptide should be proportional only to the amount of its messenger RNA available for translation. The relative rates of viral polypeptide synthesis were not altered by this treatment, suggesting that viral messenger RNA molecules coding for each polypeptide are translated with similar average frequencies. Rates of peptide chain growth were compared by following the incorporation of 3H-amino acids into completed viral polypeptides following a pulse-label. The time necessary to achieve maximum incorporation of isotope into each completed viral polypeptide was taken as its translation time, the time necessary to synthesize and release a completed molecule. We were able to determine translation times for the M and G polypeptides by this method and found that they correlated directly with their molecular weights, suggesting that nascent chains of these two polypeptides are propagated at similar rates.