Transcriptional activator of immediate-early (IE) gene products (alpha genes). Acts as a key activator of lytic infection by initiating the lytic program through the assembly of the transcriptional regulatory VP16-induced complex composed of VP16 and two cellular factors, HCFC1 and POU2F 1. VP16-induced complex represents a regulatory switch: when it is on, it promotes IE-gene expression and thus lytic infection, and when it is off, it limits IE-gene transcription favoring latent infection (By similarity). May play a role in the aggregation of tegument proteins around nucleocapsids during virus morphogenesis. Interacts with VP22. Interacts with gH (via C-terminus). Interacts with the virion host shutoff protein (vhs). Interacts with VP11/12. Associates with the VP16-induced complex; binding to host HCFC1 activates VP16 for association with the octamer motif-binding host protein POU2F1, to form a multiprotein-DNA complex responsible for activating transcription of the viral immediate early genes (By similarity). The transcriptional activation region seems to target many proteins of the RNA polymerase II transcription machinery. Belongs to the herpesviridae tegument protein VP16 protein family.