Figure 1.

Tb³⁺ cleavage of the ligand-free and pre-folded btuB riboswitch of E. coli incubated with increasing concentrations of TbCl₃ from left to right (0.0, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1.0, 2.5, 5.0, 7.5, 10, 15, 20 mM). The nucleotides undergoing a distinct cleavage in the presence of TbCl₃ are indicated on the right side. The white box indicates the supposedly helical region of P12 encompassing nucleotides 123–135. NR, Non-reacted RNA; T1, RNase T1 ladder; OH, alkaline hydrolysis ladder. The Mg²⁺ concentration was held constant at 20 mM.