FIGURE 3.

Comparison of experimental smFRET and simulated response of the riboswitch RNA to varying Mg²⁺ concentrations. (A) Histograms of the populations obtained in the smFRET experiments (exp) (dark blue) and in the coarse-grained simulations (sim) (red) at different Mg²⁺ concentrations. n_exp describes the number of molecules represented in the experimental histograms. The experiments were fitted with three Gaussians corresponding to the three states. The dark blue solid line represents the main state at the conditions, the other states are shown as a dashed line. The simulations were fitted with 1 Gaussian (red line) since at each concentration predominantly one state was populated while the probability of the other states was negligibly small. The maximum of the Gaussian fits E_FRET,exp and E_FRET,sim corresponds to the FRET efficiency of the most probable structure of each state and is shown as inset. (B) Experimental fraction of riboswitches in the three states at various Mg²⁺ concentrations. The fractions were calculated from the area under the fits (shown in A). (C) Comparison of most probable FRET efficiency E_FRET (corresponding to the maxima in the Gaussian fits shown in A) from experiments and simulations at various Mg²⁺ concentrations.