Functional dissection of TFIIB domains required for TFIIB-TFIID-promoter complex formation and basal transcription activity.

The protein TFIIB is a general transcription initiation factor that interacts with a promoter complex (D.DNA) containing the TATA-binding subunit (TFIID tau, or TBP) of TFIID to facilitate subsequent interaction with RNA polymerase II (ref. 2) through the associated TFIIF (ref. 3). The potential bridging function of TFIIB raises the possibility of two structural domains and emphasizes the importance of TFIIB structure-function studies for a further understanding of preinitiation complex assembly and function. Here we show that human TFIIB (refs 5,6) is comprised of functionally distinct N- and C-terminal domains. The C-terminal domain, containing the direct repeats and associated basic regions, is necessary and sufficient for interaction with the D.DNA complex. By contrast, the N-terminal domain that is dispensable for formation of the TFIID tau-TFIIB-promoter (D.B.DNA) complex is required for subsequent events leading to basal transcription initiation. On the basis of these results, we discuss structural and functional similarities between TFIIB and TFIID tau, which have similar structural organization and motifs.