FIG. 6.

Effect of the growth medium, the presence of ammonium, and temperature on tir expression. EPEC E2348/69 derivatives carrying the tir-cat fusions described in the legend to Fig. 5 were grown at 37°C in DMEM, DMEM plus 20 mM ammonium sulfate, or LB (A) or in DMEM at 37, 25, or 40°C (B). CAT specific activities from samples obtained at an OD₆₀₀ of 1.4 were determined and plotted. The plots of the activities determined from samples obtained along the growth curve at other OD₆₀₀ values showed the same pattern. Values are the averages of data from at least three different experiments; error bars indicate standard deviations.