Epstein-Barr virus (EBV) is a human herpesvirus with tropism for B lymphocytes and epithelial bells. EBV causes infectious mononucleosis and lymphoproliferative disease and is associated with several malignancies, including Burkitt's lymphoma, nasopharyngeal carcinoma, and Hodgkin's disease. EBV establishes a latent infection in B lymphocytes and causes indefinite cell proliferation. However, the latently infected cells can be reactivated in vitro by induction of the expression of the key immediate-early gene, BZLF1 (Z), which leads to switch from latency to cytolytic replication. Recently, Dr. Pagano's laboratory found a virally encoded Z-modulatory gene product termed RAZ. RAZ is a chimeric form of BRLF1 and BZLF1 gene products, and acts as a transdominant repressor. In vitro, RAZ heterodimerizes with Z, to which it is related, and causes Z- induced transactivation and the reactivation cascade. This proposal is a follow-up to the discovery of RAZ and its initial characterization that focuses on the biologic role of this novel chimeric protein and the mechanism of its effects on primary infection, transformation, and viral reactivation. The generation and selection of RAZ knock-out mutant virus is proposed. Characterization of the mutant virus in primary infection efficiency, transformation efficiency and viral reactivation are also proposed in detail This project will enable us to determine clearly the role of RAZ in its actual viral context. Understanding RAZ function will deepen our understanding of EBV gene regulation and eventually may lead to control and treatment of EBV-associated disease.