Figure 5.

Modular characteristics of the class I induction element. (A) Sequence and secondary structures of allosteric ribozyme constructs containing either an FMN, theophylline, or ATP aptamer [constructs I(f), I(t), and I(a), respectively]. The terminal A⋅G or G-C base pairs of each aptamer (denoted by asterisks) are interactions stabilized by ligand binding. (B) Qualitative assessment of the specificity of ligand-induced ribozyme self-cleavage. Internally ³²P-labeled constructs were incubated at 23°C for 15 min in the absence (−) or presence of FMN (F; 200 μM), theophylline (T; 1 mM), or ATP (A; 1 mM). (C) Kinetic parameters k_obs⁻ (○) and k_obs⁺ (●) determined for each allosteric ribozyme construct in the absence or presence of its cognate ligand, respectively. (D) Allosteric activation of ribozyme function (k_obs⁺/k_obs⁻) is depicted for each construct.