Figure 4.

The N-terminal domain of TFIIB is required for the transient-to-stable binding transition. (A) Scheme: Differentially labeled FL and N-terminal (1–106)-deleted (ΔN) TFIIB (4 nM each; false-colored in green and magenta, respectively) were incubated with unlabeled (black) TFIID, TFIIA, TFIIF, and Pol II for binding to immobilized DNA templates. (B) Colocalization of FL and ΔN TFIIB to the supercore or mutant promoter-containing DNA templates during a 27-min (1600-sec) incubation. (C) A representative fluorescence time trace showing the binding of FL and ΔN TFIIB proteins to a DNA template containing the supercore promoter. Insets show zoomed-in views. Transient to stable TFIIB binding was observed with ∼50% of the DNA bound by TFIIB, and, among all of these transitions, most of the stable bindings (238 out of 240) were from the FL TFIIB. (D) All TFIIB-binding events are represented by bars (height depicts residence time) to highlight the long events, which are vastly outnumbered by the short ones in the histograms (insets).