Plays a role in the expression of late transcripts bridging viral DNA replication and late gene expression during infection (PubMed:21367901). Functions concordantly with UL87 to initiate transcription from over half of all active viral promoters in late infection, without affecting host transcription. Acts on and binds to viral early-late and late kinetic-class promoters (PubMed:34339482). Localizes in replication compartments during virus infection. Belongs to the herpesviridae UL79 family.