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 from the latent infection to the lytic cycle. EB1 belongs to the Jun, Fos, ATF, CREB, C/EBP and GCN4 family of proteins, carrying a sequence-specific DNA-binding domain called "basic-Zipper" (bZIP). The N-terminal region of EB1 is required for transcriptional activation, whereas the C-terminal region contains the DNA-binding domain. The mechanism by which site-specific transcription factors increase specific initiation at polymerase II dependent promoters is thought to occur via recruitment and stabilization of components that form the initiation complex, i.e., TFIID, TFIIA, TFIIB, TFIIE, TFIIG, TFIIH, TFIIJ and pol II. TFIID is not a single protein but consists of the TATA-binding protein TBP plus several distinct and tightly associated proteins called TAFs. More specifically, in vitro studies have revealed that the TAFs are not required for basal transcription, but are essential for mediating regulated transcription by different upstream activators. TFIID binding at the promoter sites is one of the limiting steps in the assembly of the initiation complex. Direct interactions with TBP or with one or several TAFs, mediated by the activation domain of site specific activators, 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 domain, likely the region contacting the DNA rather than the activation domain, which is required for physical contact between EB1 and TBP.