Epstein-Barr virus (EBV) is a human tumor virus that is etiologically associated with nasopharyngeal and gastric cancer, Burkitt's, Hodgkin's and immunoblastic lymphoma and other human cancers. In all EBVassociated tumors and in normal B cells, the virus remains in a latent state of limited gene expression. The virus must be reactivated into its lytic cycle in order to spread between cells and among individuals. The EBV/Rta protein encoded in the viral BRLF1 gene plays an obligatory role in mediating the switch between latency and lytic cycle gene expression, acting both as a transcription factor and a replication protein. Rta is thus is a key factor in pathogenesis and oncogenesis. Our global objectives are to understand the control of BRLF1 expression, the mechanism of action of Rta and the ways Rta might manipulate expression and localization of cellular proteins. The proposed experiments are derived from many recent publications and extensive preliminary data that investigated control of expression and regulation of activity of EBV/Rta and its homologue KSHV/ORF50. We will address unsolved mysteries: Which cellular proteins regulate expression of Rta? Why do some cells respond to lytic inducing stimuli by expression of Rta while other cells are refractory? How does Rta function both as a transcription factor and replication protein? How does Rta alter the function and localization of key cellular proteins? Accordingly, our specific aims are 1) To determine the capacity and importance of cellular immediate-early proteins, such as early response and orphan nuclear receptor proteins, to activate Rta expression; 2) To understand the function of Rta in EBV DNA replication, particularly the role of phosphorylation and regulation of DNA binding; and 3) To delineate the function of Rta in expression, activation and re-Iocalization of the DNA damage response cohesin, SMC1, STAT3 and PolyA binding protein. The proposed studies, utilizing tools of cell biology, biochemistry, molecular genetics, and immunology address both basic questions of control of eukaryotic gene expression that are relevant to cancer and specific unresolved issues about molecular pathogenesis of an important human cancer virus for which there is yet no specific prevention or treatment.