Figure 4.

Kinetic analysis of individual YPT/yopE::gfp cells following a simultaneous shift of temperature and Ca²⁺ levels. The YPT/yopE::gfp strain was cultured as described in Figs. 1 and 2 except that following dilution, the culture was incubated for 3 hrs at 26 °C at which time the temperature was shifted to 37 °C and EGTA was added ([EGTA/Ca²⁺] = 2). At the indicated time points cells were removed and analyzed for YopE and GFP protein levels by immunoblotting (inset) as in Fig. 1B and fluorescence as described in Fig. 3. In each column, 500-600 cells were plotted from at least three different fields. The fluorescent levels of bacteria analyzed at the 120, 150, and 180 sampling points are normally distributed around the mean (α = 0.05) and the coefficient of variation (standard deviation/mean of the absolute signals) was calculated as 0.2, 0.18, and 0.17, respectively.