Infection by Kaposi's sarcoma-associated herpesvirus (KSHV; also called human herpesvirus 8) is a key factor in the development of Kaposi's sarcoma (KS), a proliferative lesion of endothelial cells that until recently was the commonest neoplasm of AIDS patients. In KS tumors, the viral genome resides within the majority of spindle cells in a latent state; smaller numbers of tumor cells display lytic infection. This grant began with the examination of viral gene expression in KS tumors, identifying several latent and lytic genes expressed in that context. The present renewal application seeks to further characterize the expression and function of these genes. Specifically, we will (i) develop an endothelial cell culture model of KSHV latency and use it to develop a genetic system for the creation and analysis of mutant KSHV genomes; (ii) characterize the phenotypic consequences of expression of a major KSHV latency locus encoding orfs 71,72 and 73; (iii) further explore the mechanisms and consequences of constitutive signaling by the KSHV K1 protein; (iv) characterize the biochemical activities and interactions of the KSHV kaposin gene products; and (v) identify the constituents of an abundant viral ribonucleoprotein complex and determine their function.