Inhibition of growth of E. coli cells expressing wild-type or mutant TthL4 protein by erythromycin. Cells were grown at 37°C in LB medium containing 50 μg/mL ampicillin and erythromycin at the indicated concentrations until the optical density of the control culture (cells expressing wtTthL4 and grown in the absence of erythromycin) reached the value 1.000 at 600 nm. This optical density was taken as 100%. Overproduced protein: (•) wtTthL4, (○) TthL4-G55E, (▪) TthL4-G55S, (□) TthL4-E56D, (▴) TthL4-E56Q, and (▵) TthL4-G55E-E56G.