Fig. 4. Competitive inhibition between CopA and different RNA variants for the formation of the stable CopA–CopT complex. (A) The inhibitory RNAs used in this study and their corresponding Ki values are shown. Experimental conditions are described in detail in Materials and methods. Nucleotides that are not complementary to CopT are boxed. (B) Determination of the Ki values for CopI and RNA R4. The ratio vo/vi was calculated from the inhibition experiments using different concentrations of CopI (open circles) or of RNA R4 (closed circles) at time intervals between 1 and 6 min at 37°C, and are plotted against the inhibitor concentrations.