Immediate-early transcription factor that controls the initiation of viral lytic gene expression and lytic reactivation from latency. Triggers lytic replication, and initiates a cellular senescence program in epithelial cells. Up-regulates human DCR3/TNFRSF6B by directly binding to its receptor (By similarity). Interacts with human ATF7IP protein, leading to promote and regulate host genes in virus-infected cells. Belongs to the herpesviridae Rta family.