Figure 10.

RacF1 is not essential for fluid- and solid-phase uptake. Pinocytosis, exocytosis, and phagocytosis rates were assayed in AX2 and racF1⁻ cells. (A) Pinocytosis of FITC-dextran. Cells were resuspended in fresh axenic medium at 5 × 10⁶ cells/ml in the presence of 2 mg/ml FITC-dextran. Fluorescence from the internalized marker was measured at selected time points. (B) Fluid-phase exocytosis of FITC-dextran. Cells were pulsed with FITC-dextran (2 mg/ml) for 3 h, washed, and resuspended in fresh axenic medium. Fluorescence from the marker remaining in the cell was measured. (C) Phagocytosis of TRITC-labeled yeast cells. Dictyostelium cells were resuspended at 2 × 10⁶ cells/ml in fresh axenic medium and challenged with fivefold excess fluorescent yeast cells. Fluorescence from internalized yeasts was measured at the designated time points. Data are presented as relative fluorescence, AX2 being considered 100%. All values are the average of three independent experiments.