Figure 3.

¹⁹F NMR experiments on HhRz-FU4. (A) A ¹⁹F NMR spectrum of HhRz-FU4 in 25 mM Tris⋅HCl (pH 7.5), 50 mM NaCl. A total of 26,800 transients were collected from a 40 μM solution of the RNA. All spectra were recorded at 27°C and referenced externally to 5-FU in 25 mM Tris⋅HCl (pH 7.5). (B and C) Plots of the chemical shift (ppm) of the FU4 ¹⁹F resonance as a function of added Mg²⁺ concentration in 10 mM Tris⋅HCl (pH 7.5) with either 10 (B) or 50 mM (C) NaCl. The lines are the fits according to the two-state transition model. (Insets) The linewidth (Hz) of the ¹⁹F resonances (selecting spectra recorded with ≥15,000 transients) as a function of Mg²⁺ concentration. The lines are the fits according to the two-state model.