In vitro stimulation of specific RNA polymerase II-mediated transcription by the pseudorabies virus immediate early protein.

Nuclear extracts from human cells infected with pseudorabies virus (PRV) exhibited higher levels of accurate transcription of RNA polymerase II genes than did control extracts from mock-infected cells. Stimulation was maximal at low DNA concentrations and was not gene-specific. It was heat sensitive in extracts from cells infected with a virus containing a temperature sensitive mutation in the immediate early (IE) gene. The stimulatory activity copurified from the IE protein and was also heat sensitive when purified with cells infected with tsG, further indicating that the IE protein was responsible for this stimulation. These results thus demonstrate an in vitro system that mimics, at least in part, the in vivo stimulatory action of the PRV IE protein. They further imply that the IE protein acts not by increasing the amounts of cellular transcription factors, but rather by directly or indirectly altering their activities.