Fig. 4.

CYT-18 dissociation kinetics. CYT-18 (200 nM) was incubated with trace radiolabeled E^ΔP5abc ribozyme (~3 nM) to give populations of largely native or misfolded ribozyme (circles and squares, respectively; see Methods). Complex dissociation was then followed upon addition of excess unlabeled E^ΔP5abc (2 µM). Filled symbols show results without unlabeled ribozyme (again, circles and squares represent native and misfolded ribozyme, respectively). For the reaction with native ribozyme, the major phase gave a rate constant of 0.024 ± 0.018 min⁻¹. The endpoint, 0.16 ± 0.05, is in the range expected from the 10-fold excess of unlabeled ribozyme, approximately 60% of which is expected to be native (with most of the remainder misfolded). In experiments monitoring dissociation from misfolded ribozyme, most of the labeled RNA dissociated before the first time point. A minor phase gave a rate constant of 0.042 ± 0.034 with an amplitude of ~0.1. The endpoint, 0.02 ± 0.018, is lower than in reactions with the native ribozyme, despite the same 10-fold excess of unlabeled ribozyme chase, presumably because the labeled misfolded ribozyme competes poorly with the native ribozyme in the chase.