Fig. 4. Antibody-induced endocytosis is not sufficient for targeting of Syt IX to the ERC. RBL cells stably transfected with Flag-Syt IX-GFP cDNA were grown on glass coverslips. Cells were then incubated with monoclonal anti-Flag antibodies (10 µg/ml) for 30 minutes at 4°C, washed and subsequently shifted to 37°C for the indicated time periods (A) or for 2 hours (B). The reaction was stopped by placing the cells on ice. Cells were either labeled with Cy3-conjugated donkey anti-mouse IgG (A) or were allowed to internalize Texas Red-conjugated human Tfn for the last 10 minutes of incubation (B). Bars, 3 µm. Arrows mark the vesicular localization of Flag-Syt IX-GFP and Tfn.