Figure 2.

Evolution of catalytic activity in Ca²⁺ or Mg²⁺. Apparent rate constants (k_obs) were determined by single-time-point assays of self-cleavage for every third generation of RNA. Measurements were within the linear ranges of the reactions. Precursor and product RNAs were quantitated by phosphorimaging. Values were normalized to the rate constants determined for native TP292 in either Ca²⁺ or Mg²⁺. (n.b. the absolute value of k^Mg/k^Ca for native TP292 is ≈1.6 × 10⁴). (Inset) Autoradiographs of single-time-point, self-cleavage assays of selected RNA populations performed in either Ca²⁺ (100 mM CaCl₂, pH 8.0) or Mg²⁺ (25 mM MgCl₂, pH 6.0). (−) TP292 RNA incubated in the absence of divalent metal. TP, native TP292 RNA; Pre, full-length TP292 RNA; Mat, TP292 RNA minus the 5′ leader element.