DESCRIPTION: (Applicant's Description): The EBV/R transactivator (Rta), an immediate-early product with homologues among other oncogenic gamma- herpesviruses, plays an essential role in mediating the switch from latency to lytic cycle gene expression. The mechanism of action of Rta is complex: It activates some promoters directly, and others indirectly by means of unidentified proteins. Yet other programs are activated as a result of synergy between ZEBRA and Rta. Our global objective is to shed light on the mechanism of activation of these three classes of viral promoters. The experiments are derived from recent original observations in our laboratory about the rich biology of Rta. In some B cell background Rta activates ZEBRA and thus the entire lytic cascade. In other cell backgrounds, however, Rta activates downstream target genes without activation ZEBRA. Certain point mutants of ZEBRA, e.g. Z(S186A), that are unable to activate Rta expression and hence are incapable of disruption of latency, are nonetheless fully competent to synergize with Rta. In B cells that are dually infected with EBV and KSHV each Rta homologue selectively activates expression of autologous lytic cycle gene. Accordingly our AIMS are: I) to study the mechanism by which EBV/Rta directly activates certain EBV promoters in a manner independent of the action of ZEBRA. ii) To study the indirect mechanism by which EBV/Rta activates expression of its own promoter. iii) To attempt to understand cell-virus background effects on the capacity of Rta to activate its own promoter. iv) To study the mechanism by which EBV/RTA synergizes with ZEBRA on certain promoters. v) To determine the basis of viral specificity of the EBV/Rta and KSHV/Rta proteins in dually infected cells. The studies proposed thus address fundamental, though complex issues of viral gene regulation in the context of an intact viral genome.