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| Modern Genetic Analysis Chapter 14. Regulation of Gene Transcription Transcription: Gene Regulation in Eukaryotes an Overview Figure 14-23. (a) Assembly of the RNA polymerase II initiation complex begins with the binding of TFIID to the TATA box. TFIID is composed of one TATA box-binding subunit called TBP (dark blue) and more than eight other subunits (TAFs), represented by one large symbol (light blue). Inhibitors can bind to the TFIID-promoter complex, blocking the binding of other general transcription factors. Binding of TFIIA to the TFIID-promoter complex (to form the DA complex) prevents inhibitor binding. TFIIB then binds to the DA complex, followed by binding of a preformed complex between TFIIF and RNA polymerase II. Finally, TFIIE, TFIIH, and TFIIJ must add to the complex, in that order, for transcription to be initiated. (b) TATA-binding protein (blue) is a remarkably symmetrical, saddle-shaped molecule. Its underside rides on DNA and seems to bend it. This bending may somehow facilitate assembly of the complex that initiates transcription. (Part a from H. Lodish, D. Baltimore, A. Berk, S. L. Zipursky, P. Matsudaira, and J. Darnell, Molecular Cell Biology, 3d ed. Copyright © 1995 by Scientific American Books; part b courtesy of J. L. Kim and S. K. Berley, from Nature 365, 1993, 520.)

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