Figure 3.
(Top) Our second design places two target-binding sites within the beacon’s single-stranded loop, rendering it possible to stabilize the stem (i.e., increase the energy gap between the two binding events) without altering specificity. (Bottom) Using a rather stable stem and a 14-base target this achieves a Hill coefficient of 1.94±0.17 and a dynamic range of 9.6(±1.6)-fold, within error of ideal behavior. Shorter targets and/or less stable stems reduce cooperativity by reducing the energy gap between the first and second binding events (Figures SI1, SI2).