FIGURE 2.
Alanine mutants of previously identified FusR residues in E. coli EF-G are also strongly resistant to fusidic acid in vitro. We measured the ability of fusidic acid to suppress GTP hydrolysis catalyzed by EF-G proteins in the presence of the ribosome, excess GTP, and variable concentrations of fusidic acid (as indicated on the x axis). Rates (v) of reactions were determined as described under “Experimental Procedures.” Data of 1/v as a function of fusidic acid concentration are plotted. The inhibitory constant (Ki) for fusidic acid binding to EF-G corresponds to the x axis intercept, i.e. the fitted line through the data points and extrapolated to the x axis. Ki values (in μm) for wild-type and mutant EF-G proteins are given in parentheses.