Figure 1.

(A) PIC assembly begins with TFIID recognizing the TATA element, followed by coordinated accretion of TFIIB, the nonphosphorylated form of pol II (pol IIA) plus TFIIF, TFIIE, and TFIIH. Before elongation pol II is phosphorylated (pol IIO). Following termination, a phosphatase recycles pol II to its nonphosphorylated form, allowing the enzyme to reinitiate transcription in vitro. TBP (and TFIID) binding to the TATA box is an intrinsically slow step, yielding a long-lived protein–DNA complex. Efficient reinitiation of transcription can be achieved if recycled pol II reenters the preinitiation complex before TFIID dissociates from the core promoter. (Adapted from ref. 5.) (B) Schematic representation of functional interactions that modulate basal (Upper) and activator-dependent transcription (Lower). The basal factors TBP, TFIIB, TFIIF, TFIIE, and TFIIH and pol II are denoted by yellow symbols, with the general initiation factor contents of a “pol II holoenzyme” enclosed by square brackets. TAF_II and non-TAF_II coactivators (purple) and transcriptional activators (green) are shown interacting with their targets in the PIC. (Figure courtesy of R. G. Roeder and S. Stevens, The Rockefeller University.)