The activation domain of herpesvirus saimiri R protein interacts with the TATA-binding protein

The herpesvirus saimiri open reading frame (ORF) 50 produces two transcript s. The first is spliced, contains a single intron, and is detected at early times during the productive cycle, whereas the second is expressed later a nd is produced from a promoter within the second exon. Analysis of their ge ne products has shown that they function as sequence specific transactivato rs. In this report, we demonstrate that the carboxy terminus of ORF 50b con tains an activation domain which is essential for transactivation. This dom ain contains positionally conserved hydrophobic residues found in a number of activation domains, including the herpes simplex virus VP16 and the Epst ein-Barr virus R proteins. Mutational analysis of this domain demonstrates that these conserved hydrophobic residues are essential for ORF 50 transact ivation capability. Furthermore, this domain is required for the interactio n between the ORF 50 proteins and the basal transcription factor TATA-bindi ng protein.