Effects of temperature on viral RNA synthesis and RNA polymerase activity in a foot-and-mouth disease virus system

Summary

The synthesis of the RNA of a Foot-and-Mouth Disease Virus mutant was studied in infected BHK cells during a single cycle at 36°C (optimal temperature) and 39°C (supra-optimal temperature).

The amount of synthesized RNA was estimated by studying the kinetics of³H uridine incorporation into acid-insoluble material. The results indicated that viral RNA synthesis was inhibited by 70% at 39°C as compared with controls maintained at 36°C.

Limited RNA production at the supra-optimal temperature does not reflect a decrease of catalytic activity of the RNA polymerase at 39°C as measured in a standardin vitro assay system after its extraction from infected cells. The enzyme showed a somewhat increased activity at 39°C as compared with 36°C.

The hypothesis that degradation of the RNA molecules occurs at elevated temperature, thus masking the true rate of synthesis, was disproved by short pulse labelling experiments.

In order to distinguish between the enzyme activity and its synthesis at both 36° and 39°C, temperature shift experiments were performed again, using infected cells. This kind of experiment showed that less enzyme was synthesized at 39° than at 36°C. This assumption was reinforced by the direct quantitation of the enzyme at 39°C.

It is concluded that the occurrence of a thermosensitive block in viral genome translation must be considered among other possible hypotheses which could explain this temperature effect on the infection process.