Three-dimensional structure of the human TFIID-IIA-IIB complex

The multisubunit transcription factor IID (TFIID) is an essential component of the eukaryotic RNA polymerase II machinery that works in concert with T FIIA (IIA) and TFIIB (IIB) to assemble initiation complexes at core eukaryo tic promoters. Here the structures of human TFIID and the TFIID-IIA-IIB com plex that were obtained by electron microscopy and image analysis to 35 ang strom resolution are presented. TFIID is a trilobed, horseshoe-shaped struc ture, with TFIIA and TFIIB bound on opposite Lobes and flanking a central c avity. Antibody studies Locate the TATA-binding protein (TBP) between TFIIA and TFIIB at the top of the cavity that most Likely encompasses the TATA D NA binding region of the supramolecular complex.