Close but distinct regions of human herpesvirus 8 latency-associated nuclear antigen 1 are responsible for nuclear targeting and binding to human mitotic chromosomes

Human herpesvirus 8 is associated with all forms of Kaposi's sarcoma, AIDS- associated body cavity-based lymphomas, and some forms of multicentric Cast leman's disease. Herpesvirus 8, like other gammaherpesviruses, can establis h a latent infection in which viral genomes are stably maintained as multip le episomes. The latent nuclear antigen (LANA or LNAI) may play an essentia l role in the stable maintenance of latent episomes, notably by interacting concomitantly with the viral genomes and the metaphase chromosomes, thus e nsuring an efficient transmission of the neoduplicated episomes to the daug hter cells. To identify the regions responsible for its nuclear and subnucl ear localization in interphase and mitotic cells, LNAI and various truncate d forms were fused to a variant of green fluorescent protein. This enabled their Localization and chromosome binding activity to be studied by low-lig ht-level fluorescence microscopy in living HeLa cells. The results demonstr ate that nuclear localization of LNAI is due to a unique signal, which maps between amino acids 24 and 30. Interestingly, this nuclear localization si gnal closely resembles those identified in EBNA1 from Epstein-Barr virus an d herpesvirus papio. A region encompassing amino acids 5 to 22 was further proved to mediate the specific interaction of LNA1 with chromatin during in terphase and the chromosomes during mitosis. The presence of putative phosp horylation sites in the chromosome binding sites of LNA1 and EBNA1 suggests that their activity may be regulated by specific cellular kinases.