MULTIPLE FUNCTIONAL DOMAINS OF HUMAN TRANSCRIPTION FACTOR-IIB - DISTINCT INTERACTIONS WITH 2 GENERAL TRANSCRIPTION FACTORS AND RNA POLYMERASE-II

Transcription factor IIB (TFIIB) plays a pivotal role in the formation of transcription-competent initiation complexes. TFIIB was found to i nteract with the TATA-binding protein, the small subunit of TFIIF, and RNA polymerase II. These interactions require distinct domains in TFI IB. Using the gel mobility-shift assay, it was found that the amino te rminus of TFIIB was necessary for the formation of complexes containin g RNA polymerase II and TFIIF, whereas the carboxy-terminal domain, wh ich is composed of two imperfect direct repeats and includes a putativ e amphipathic alpha-helix, was sufficient for the formation of complex es containing the TATA-binding protein and TFIIB (DB complex). Protein -protein interaction analyses demonstrate that the amphipathic alpha-h elix in TFIIB is important for the interaction with the TATA-binding p rotein. Specific residues mapping to the carboxyl terminus of the seco nd direct repeat were found to be crucial for the interaction of TFIIB and RNA polymerase II. The interaction with the small subunit of TFII F was mapped to