Figure 3.

(A) smFRET data on unfolding of O1–O5 GQ constructs by varying concentrations of RPA. The concentration quoted on each histogram represents the concentration of RPA used for that measurement. (B) Percentage of GQ molecules unfolded and bound by RPA as a function of RPA concentration for O1–O5. The red line shows a Langmuir binding isotherm fit to the data. The stability of GQ structures systematically decreases as the loop length is increased. O1–O3 molecules maintain a certain fraction of folded GQ molecules at RPA concentrations as high as 1 μM, whereas all of the O4 and O5 molecules are unfolded by <20 nM of RPA.