The effect of infection with Sindbis virus and its temperature-sensitive mutants on cellular protein and DNA synthesis

Abstract

Wild-type Sindbis virus inhibits protein synthesis by 55% and DNA synthesis by 88% in infected compared to mock infected cells at 5–7 hr after infection. Infection with temperature-sensitive (ts) mutants at restrictive temperature (39°) showed that inhibition of protein synthesis was correlated with viral RNA synthesis. All mutants able to inhibit DNA synthesis made viral RNA at 39°, but some made RNA and were unable to inhibit DNA synthesis. There was no correlation between ability to inhibit DNA synthesis and ability to inhibit protein synthesis. All mutants making a large uncleaved protein of molecular weight 144,000 were unable to inhibit DNA synthesis. Temperature-shift experiments were carried out with the mutants F104 (unable to make viral RNA at 39°) and F36 (makes viral RNA at 39°), both of which were unable to inhibit DNA synthesis. From measurements of infectious virus production, it was shown that F104 had an early mutation, whereas F36 carried a late mutation. For F104, the production of infectious virus in shift experiments mirrored ability to inhibit DNA synthesis. For F36, inhibition of DNA synthesis could be achieved by a short period at 30° before shifting to 39°; also inhibition of DNA synthesis could be achieved by shifting down from 39 to 30° throughout most of the virus growth cycle. It is concluded that inhibition of cellular DNA synthesis results from the action of one or more of the virus structural proteins or their precursors; it does not result from inhibition of cellular protein synthesis. The results are consistent with the theory that inhibition of cellular protein synthesis results from competition of viral RNA with cellular RNA for translation.