FIGURE 9-19 Model for the sequential assembly of an RNA polymerase II preinitiation complex. The indicated general transcription factors and purified RNA polymerase II (Pol II) bind sequentially to TATA box DNA to form a preinitiation complex (PIC). ATP hydrolysis then provides the energy for the unwinding of DNA at the transcription start site by a TFIIH helicase subunit that pushes downstream DNA into the polymerase. The DNA is held in position in the PIC by binding of the TATA box by the TBP subunit of TFIID, and the resulting strain on the structure of the duplex DNA assists the N-terminal region of TFIIB and Pol II to melt the DNA at the transcription start site, forming the transcription bubble. As Pol II initiates transcription in the resulting open complex, the polymerase transcribes away from the promoter, its CTD becomes phosphorylated by the TFIIH kinase domain, and the general transcription factors dissociate from the promoter. See S. Sainsbury, C. Berrnecky, and P. Cramer, 2015, Nat. Rev. Mol. Cell Biol. 16:129.