Figure 3.

Progression of strategy 2, activity-based selections. (A) Graphic representation: in each round, beginning with round 8, the activity of the pool in the presence and in the absence of 5 mM aspartame or caffeine was measured. Ratios >1 indicate increased activity in the presence of ligand. (B) Analysis of hammerhead ribozyme cleavage. The extent of cleavage of radiolabeled RNA was determined by denaturing gel electrophoresis in rounds 9–12 of the activity-based selections for a caffeine sensor. Cleavage of the pool was measured in the presence (b, d, f and h) or absence (a, c, e and g) of 5 mM caffeine.