Fig. 2. Permanganate probing of T7RNAP ITCs formed with either 3′-template strand-labeled pT7-7 (A) or pT7-8 (C). Lengths of the RNA in the complexes are as specified in Figure 1. Lanes 8, 9 and 10 contain, respectively, 0.01, 0.1 or 1 mM 3′-dUTP. Reactive Ts are labeled relative to the transcription start site (+1). (B) and (D) show scans of the reactions in (A) and (C) respectively. In (C) and (D) the doublets are due to incomplete fill-in by Klenow in the labeling reaction.