Figure 6.

Preferential interaction coefficients (Γ₂₊) for the A-riboswitch, as calculated from RNA-HQS titration experiments. Titrations were carried out at 20 °C in buffer containing 20 mM MOPS, pH 6.8, and 50mM K⁺. A) Γ₂₊ measured in the presence (black circles) or absence (gray circles) of 250 µM DAP. Error bars are standard deviations calculated from four interpolated data sets. B) ΔΓ₂₊, the difference between Γ₂₊ for folded and unfolded A-riboswitch RNA (panel A), as a function of Mg²⁺ concentration.