Pseudorabies virus early protein O transactivates the viral gene promoters

Pseudorabies virus (PRV) early protein O (EPO) contains the RING finger domain with homology to the immediate-early (IE) protein ICPO of herpes simplex virus type 1 (HSV-I). EPO was detected by indirect immunefluorescence in the nuclei of the cells transfected with EPO expression plasmid as is the case in cells infected with PRV. In transient expression assays, EPO transactivated the PRV IE, thymidine kinase (TK) and glycopretein X (gX) promoters, indicating that EPO, like ICPO of HSV-I, is a transactivating protein.