NEGATIVELY CIS-ACTING ELEMENTS IN THE DISTAL PART OF THE PROMOTER OF EPSTEIN-BARR-VIRUS TRANSACTIVATOR GENE BZLF1

Epstein-Barr virus (EBV) replicates in a latent or a lytic way in the infected organism, depending on the type and level of differentiation of the host cell. The switch between latency and lytic replication was previously shown, for Burkitt's lymphoma cell lines, to depend on the viral BZLF1 gene product. Protein-DNA assays were used to identify th e cis-acting elements that represent the link between regulating signa l transduction pathways and the viral cascade of gene expression. Spec ific binding of proteins to several sites of the BZLF1 promoter during latency was shown. Induction of the lytic cycle by stimulation with 1 2-O-tetradecanoyl-phorbol 13-acetate abolished the binding of these pr oteins to the distal promoter (positions -227 to -551), suggesting a f unctional role for the downregulation of promoter activity during late ncy. Computer analysis identified a multiply repeated sequence motif, HI, in this region and exonuclease III footprints confirmed that these sites act as specific protein recognition sites. Using a set of repor ter plasmids we were able to demonstrate a negative regulatory effect of the HI motif in some B lymphoid cell lines, in contrast to epitheli al HeLa cells. The HI silencer elements are different from other silen cer elements described so far in respect of their sequence and protein -binding pattern during the activation of BZLF1.