The identification of factors capable of reversing the core-mediated inhibition of the bluetongue virus transcriptase.

The in vitro transcription reaction of bluetongue virus (BTV) is characterized by a core-mediated, temperature-dependent inhibition at high core concentrations and temperatures (Van Dijk & Huismans, 1980; Huismans, Van Dijk & Els, 1987a). It has been found that this inhibition is reversible and that an inactivated transcriptase reaction mixture can be reactivated by lowering the temperature of the reaction from 37 degrees C to 28 degrees C. In the same way it is possible to inactivate a reaction by increasing the incubation temperature from 28 degrees C to 37 degrees C. It was also found that the inhibition is counteracted by the addition of sucrose or glycerol. At relatively low core concentrations and in the presence of sucrose it is possible to obtain conditions under which transcription at 37 degrees C is more efficient than at 28 degrees C. The latter conditions probably reflect much better the in vivo temperature optimum for the BTV transcriptase than the in vitro conditions at very high core concentrations.