Although most infections with human cytomegalovirus (HCMV) are asymptomatic, congenital infections and infection of immunocompromised (AIDS and transplant) patients can be particularly devastating. Unfortunately, the currently licensed drugs for HCMV diseases can offer only a modestly improved prognosis in some of these cases. It is, therefore, imperative to gain a more detailed understanding of the biological role and importance of viral proteins for HCMV growth as these may provide new approaches to inhibiting HCMV replication. Immediate early (IE) viral genes play a central and crucial role in viral growth and pathogenesis. In a wide variety of virus systems, individual IE proteins are either required to initiate productive infection in culture or, alternatively, affect virus growth or virus-host cell interactions in vivo. It is not known which, if any, of the HCMV IE genes are essential for progression of the lytic cycle. However, by analogy to other herpesvirses, this class of genes is certain to be important in determining the outcome of virus infection. Among the more intriguing of the HCMV IE proteins is the UL37 protein, pUL37. It is predicted to be a membrane-bound glycoprotein. pUL37 has regulatory activity for nuclear gene expression. We hypothesize that the pUL37 is essential to virus replication and may be involved in altering cellular physiology. The overall goal of this research proposal is to define the biochemical properties of pUL37, to determine its role in the virus life cycle and to investigate its possible role in initiating cell signaling. We will determine the production, location, modification of pUL37 in HCMV-infected cells using newly generated anti-pUL37 specific antisera. To determine if pUL37 is essential for HCMV growth, we will isolate HCMV UL37 mutants, using complementation systems. We will examine the ability of these mutants to grow in noncomplementing cells from different cell lineages and in growth-arrested cells. We will determine the stage(s) of the virus life cycle affected by pUL37 by examining the production of viral IE, early and late gene products and of viral DNA. We will also examine the ability of HCMV UL37 mutants to regulate nuclear gene expression. The domains sufficient for pUL37 transactivitating activity will be determined by mutational analysis. It is anticipated, because of the predicted pUL37 structure, that domains which determine cellular location of pUL37 will be required for its transactivating activity. We anticipate that these studies will determine whether or not pUL37 is essential for HCMV growth and whether it may play a role in altering cell physiology.