Schematics of continuous and discontinuous catalytic activity assays for folding. A, Continuous assay. The reaction is performed in a single stage, in which both folding and catalysis occur. Aliquots are quenched at various times t. B, Discontinuous assay. In the first stage, folding is allowed but the catalytic reaction is blocked. At various times t1, aliquots are transferred to stage 2. Here, the conditions allow robust catalysis while preventing further accumulation of native ribozyme, allowing determination of the fraction of native ribozyme at time t1.