Figure 8.

Scheme for ethidium inhibition of RNase III. The scheme includes R1.1 RNA as substrate, with the internal loop indicated by the absence of formal Watson–Crick base pairing (indicated by the horizontal bars). RNase III is shown as a dimer of ovals. Ethidium is represented by the solid bars. The inset shows the kinetic scheme for inhibition: S, E and I refer to substrate, enzyme (RNase III) and inhibitor (ethidium), respectively. Since it is not yet known whether ethidium can directly dissociate from the E·S·I complex to allow cleavage, this step is not included in the scheme (see also Results and Discussion).