Restoration of the Epstein-Barr virus ZEBRA protein's capacity to disrupt latency by the addition of heterologous activation regions.

The ZEBRA protein has a unique biological function among herpesviral proteins. It is responsible for the disruption of Epstein-Barr virus (EBV) latency and the induction of the lytic cycle. ZEBRA is a bZIP transcriptional activator which binds as a dimer to 7-bp response elements within EBV promoters and is directly involved in the stimulation of virus replication at the EBV lytic origin. We have employed the ZEBRA/EBV biological system to test whether a heterologous activation domain can substitute for another activation domain (the ZEBRA domain). The ZEBRA activation region was replaced with the potent acid activation region from the herpes simplex virus VP16 protein or with the activation region of the EBV R protein. Both chimeras were found to transactivate model and native promoters at equivalent or better levels than ZEBRA itself. Activation was not target- or cell-type dependent, nor was it dependent on the presence of virus. These activation domains restored ZEBRA's ability to induce early antigen and to stimulate origin replication to levels that were equal to or greater than those of wild type. These studies suggest that the specificities of some of the known biological functions of ZEBRA are not dependent upon the nature of the activation domain present within ZEBRA.