THE BZIP MOTIF OF THE EPSTEIN-BARR-VIRUS (EBV) TRANSCRIPTION FACTOR EB1 MEDIATES A DIRECT INTERACTION WITH TBP

The EBV transcription factor EB1, is a key determinant of the switch f rom the latent infection to the lytic cycle. EB1 belongs to the Jun, F os, ATF, CREB, C/EBP and GCN4 family of proteins, carrying a sequence- specific DNA-binding domain called ''basic-Zipper'' (bZIP). The N-term inal region of EB1 is required for transcriptional activation, whereas the C-terminal region contains the DNA-binding domain. The mechanism by which sim specific transcription factors increase specific initiati on at polymerase II dependent promoters is thought to occur via recrui tment and stabilization of components that form the initiation complex , ie., TFIID, TFIIA, TFIIB, TFIIE, TFIIG, TFIIH, TFIIJ and pol II. TFI ID is not a single protein but consists of the TATA-binding protein TB P plus several distinct and tightly associated proteins called TAFs. M ore specifically, in vitro studies have revealed that the TAFs are not required for basal transcription, but are essential for mediating reg ulated transcription by different upstream activators. TFIID binding a t the promoter sites is one of the limiting steps in the assembly of t he initiation complex. Direct interactions with TBP or with one or sev eral TAFs, mediated by the activation domain of site specific activato rs, could influence the binding rate of TFIID, and thus provide one of the mechanisms by which transcription is regulated. We show here that EB1 interacts directly with TBP in vitro, and that it is the bZIP dom ain, likely the region contacting the DNA rather than the activation d omain, which is required for physical contact between EB1 and TBP.