The Internal Kaposi's Sarcoma-Associated Herpesvirus LANA Regions Exert a Critical Role on Episome Persistence

Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen (LANA) is a 1,162-amino-acid protein that acts on viral terminal repeat (TR) DNA to mediate KSHV episome persistence. The two essential components of episome persistence are DNA replication prior to cell division and episome segregation to daughter nuclei. These functions are located within N- and C-terminal regions of LANA. N- and C-terminal regions of LANA are sufficient for TR DNA replication. In addition, N- and C-terminal regions of LANA tether episomes to mitotic chromosomes to segregate episomes to progeny cell nuclei. To generate a tethering mechanism, N-terminal LANA binds histones H2A/H2B to attach to mitotic chromosomes, and C-terminal LANA binds TR DNA and also associates with mitotic chromosomes. Here, we test the importance of the internal LANA sequence for episome persistence. We generated LANA mutants that contain N- and C-terminal regions of LANA but have most of the internal sequence deleted. As expected, the LANA mutants bound mitotic chromosomes in a wild-type pattern and also bound TR DNA as assayed by electrophoretic mobility shift assays (EMSA). The mutants mediated TR DNA replication, although with reduced efficiency compared with LANA. Despite the ability to replicate DNA and exert the chromosome and DNA binding functions necessary for segregating episomes to daughter nuclei, the mutants were highly deficient for the ability to mediate both short-and long-term episome persistence. These data indicate that internal LANA sequence exerts a critical effect on its ability to maintain episomes, possibly through effects on TR DNA replication.