Impaired phagocytosis in GFP-YopE expressing cells. (A) Cells were allowed to phagocytose TRITC-labeled yeast particles on coverslips for 30 minutes before fixation. Arrows indicate yeast particles internalized by Dictyostelium cells. Note that cells expressing large amounts of the GFP fusion have no internalized particles. Scale bar, 25 μm. (B) Cells were treated as in A and scored for the presence of internalized particles. Control cells are cells of the parental strain MB35 expressing GFP. The intensity of GFP expression was quantitated with Image J. The diagrams display the distribution of the corresponding cell population according to the GFP levels. The populations were divided in 10 equally large classes and the proportion of phagocytosing cells was calculated. 259 control and 271 GFP-YopE cells from 4 coverslips were scored. *P < 0.05 relative to the average proportion of phagocytosing cells in the control population.