FUNCTIONAL DISSECTION OF TFIIB DOMAINS REQUIRED FOR TFIIB-TFIID-PROMOTER COMPLEX-FORMATION AND BASAL TRANSCRIPTION ACTIVITY

THE protein TFIIB is a general transcription initiation factor1 that i nteracts with a promoter complex (D.DNA) containing the TATA-binding s ubunit (TFIIDtau, or TBP) of TFIID to facilitate subsequent interactio n with RNA polymerase II (ref. 2) through the associated TFIIF (ref. 3 ). The potential bridging function2,4 of TFIIB raises the possibility of two structural domains and emphasizes the importance of TFIIB struc ture-function studies for a further understanding of preinitiation com plex assembly and function1. 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 bask re gions, is necessary and sufficient for interaction with the D.DNA comp lex. By contrast, the N-terminal domain that is dispensable for format ion of the TFIIDtau-TFIIB-promoter (D.B.DNA) complex is required for s ubsequent events leading to basal transcription initiation. On the bas is of these results, we discuss structural and functional similarities between TFIIB and TFIIDtau, which have similar structural organizatio n and motifs5.