IDENTIFICATION OF CRITICAL CIS ELEMENTS INVOLVED IN MEDIATING EPSTEIN-BARR-VIRUS NUCLEAR ANTIGEN 2-DEPENDENT ACTIVITY OF AN ENHANCER LOCATED UPSTREAM OF THE VIRAL BAMHI C-PROMOTER

The six genes encoding the Epstein-Barr virus nuclear antigens (EBNAs) are transcribed from one of two promoters, BamHI C promoter (Cp) or BamHI W promoter (Wp), located near the left end of the viral genome. During the establishment of viral latency in B lymphocytes, Wp is used exclusively before a switch to Cp usage. We and others have previously identified an enhancer in the region upstream of Cp which requires EBNA 2 for activity (M. Woisetschlaeger, X. W. Jin, C. N. Yandava, L. A. Furmanski, J. L. Strominger, and S. H. Speck, Proc. Natl. Acad. Sci. USA 88:3942-3946, 1991; N. S. Sung, S. Kenney, D. Gutsch, and J. S. Pagano, J. Virol. 65:2164-2169, 1991). Infection of B lymphocytes with a mutant virus lacking the EBNA 2 gene results in prolonged usage of Wp and failure to switch to Cp usage, indicating that EBNA 2 transactivation of the enhancer upstream of Cp may be critical for promoter switching. In this study, we have defined the minimal EBNA 2-dependent enhancer by using a series of deletion mutants. The results of site-directed mutagenesis revealed that there are three regions of the enhancer that are important for activity, two of which appear to bind B-lymphocyte-specific factors.