Kaposi's sarcoma-associated herpesvirus (KSHV) also called Human herpes virus type 8 (HHV-8) is associated with Kaposis's sarcoma (KS), and two lymphoproliferative diseases: Primary effusion lymphomas (PEL) and a subset of Multicentric Castlemen's disease (MCD). Common to these malignancies is that the majority of tumor cells are latently infected and express only a small number of viral genes. One of these genes, ORF73, encodes the latency-associated nuclear antigen (LANA). LANA is highly expressed in all KS tumor cells and plays an important role in the biology of KSHV. LANA is the only viral protein required for latent DNA replication and genome maintenance during latency. In addition, LANA interacts with a variety of cellular proteins including the tumor suppressors p53 and Rb thereby modulating gene expression in latently infected cells. To analyze LANA's ability to modulate cellular gene expression, we performed gene expression profiling and found that LANA regulates a number of genes in the Rb/E2F pathway which, as a consequence can protect lymphoid cells from p161NK4a-induced cell cycle arrest. To study LANA's role in DNA replication we performed a detailed biochemical analysis of its DNA binding specificity and activity. We identified two binding sites within the terminal repeat of the KSHV genome and demonstrated that both sites contribute to the ability of LANA to support replication of TR-containing plasmids. We hypothesize that LANA and/or cis-regulatory sequences within TR interact with cellular proteins that facilitate DNA replication. To address this hypothesis we propose the following three aims that are focused on deciphering mechanisms by which LANA supports DNA replication: 1) Mapping cis-regulatory sequences of the putative origin of replication within TR 2) Mapping trans-requirements for DNA binding and LANA-dependent DNA replication 3) Identification of cellular proteins that interact with LANA-C and/or a minimal origin of replication.