Fig. 3.

(A) Array of 1D selective spin-echo spectra obtained upon injecting hyperpolarized water and hypoxanthine into a solution of the GSR aptamer. The final concentration of RNA was ∼170 μM and of ligand ∼340 μM. Spectra were recorded as in Fig. 1 with a time resolution of 0.33 s; the first data point was discarded due to turbulence present at the start of acquisition. Multiple peaks display site-specific kinetics associated with structural changes induced by the binding of the hypoxanthine; some of these are highlighted with different colors. (B) Buildup plots for several bases indicating folding kinetics on the time scale of ∼1 s. As a control, evolution of U81 is plotted to show that some bases do not experience changes upon binding. Buildup curves with different colors correspond to peaks highlighted accordingly in the spectral time series.