The Zta trans-activator protein stabilizes TFIID association with promoter DNA by direct protein-protein interaction.

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Abstract
Eukaryotic transcriptional activators are believed to stimulate transcription through direct and/or indirect interactions with one or more of the general transcription factors. We show here that the Zta transcriptional activator protein encoded by the Epstein-Barr virus makes direct physical contact with the basic transcription factor TFIID. Both Zta and TFIID were expressed in and purified from Escherichia coli. Zta stabilized the binding of TFIID to Zta-responsive promoters as assayed by gel electrophoresis mobility-shift and immunoprecipitation of radiolabeled promoter DNA. A deletion mutant of Zta that failed to activate transcription failed to stabilize TFIID binding. DNase I footprinting showed that Zta reduced the dissociation rate of TFIID bound to the TATA element. Protein blotting and immunoprecipitation experiments demonstrated that TFIID and Zta also interact in the absence of promoter DNA. The amino acid residues 25-86 of Zta were essential for the stable association with TFIID and were shown to be required for trans-activation in vivo. We propose that Zta stimulates transcription, in part, by direct physical contact with the conserved domain of TFIID and the formation of a stable Zta-TFIID-promoter complex.

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