The conformation of the transcription factor TFIIB modulates the response to transcriptional activators in vivo.

The general transcription factor TFIIB plays a crucial role in the assembly of the transcriptional preinitiation complex and has also been proposed as a target of transcriptional activator proteins (reviewed in [1]). TFIIB is composed of two domains which are engaged in an intramolecular interaction that is disrupted upon interaction with the activation domain of the Herpesvirus VP16 protein in vitro [2] [3]. The significance of this event for transcriptional activation is not known, however. The amino-terminal intramolecular interaction domain is the most conserved region of TFIIB and plays a role in transcription start-site selection [4] [5] [6]. In addition, we have shown previously that the integrity of this region is required for transcriptional activation in vivo [4]. Here, we have defined a charge cluster at the amino terminus of TFIIB that is required for transcriptional activation in vivo. We found that this domain determines the affinity of the TFIIB intramolecular interaction and the ability of TFIIB to interact with a transcriptional activation domain, but not with components of the holoenzyme. Our results suggest that the intramolecular interaction in TFIIB regulates transcriptional activation in vivo.