A virion protein (VP16) of herpes simplex virus (HSV) activates transcription of viral immediate-early genes. We have determined the nucleotide sequence of the virion activator gene from HSV-2, which we term VP16-2. Comparison of the deduced amino acid sequences of the HSV-1 and HSV-2 homologs shows that the VP16-2 gene product retains features determined to be important for transcriptional activation by VP16.