The Escherichia coli ribB riboswitch senses flavin mononucleotide within a defined transcriptional window

RNase H assays of transcription complexes located at positions 175 and 247. (A) K_switch determination using the probe 137 for the elongation complex stalled at position 175 (EC-175). Cleavage assays were performed using a range of 100 pM to 500 µM FMN. The K_switch value (23 ± 3 nM) was obtained using the probe 137. The experiments were performed in triplicate, and the most representative data are shown. (B,C) K_switch determination using the probes 137 (B) and 184 (C) for the elongation complex stalled at position 247 (EC-247). Cleavage assays were performed using a range of 100 pM to 500 µM FMN. For each probe, a small change in cleavage efficiency was observed across the FMN concentrations, thus leading to a greater uncertainty of the determined K_switch values. The experiments were performed in triplicate, and the most representative data are shown.