FIGURE 6.

Transcriptionally active PICs formed with pol II(G) are fully stimulated by TFIIF during subsequent transcript elongation. Pol II was incubated with a 20-fold excess of Gdown1 or with buffer, followed by PIC assembly (containing 72 fmol of TFIIF), pulse-labeling, high salt rinse, and chase in the absence or presence of 166 fmol of TFIIF as described under “Experimental Procedures.” Lanes 6–8 contained 8× the standard reaction amount to increase signal for analysis. A schematic of the assay is shown to the right of the gel.