The effect of overexpression of Abp1 domains and mutants on the movement of the BCR from the cell surface to late endosomes. A, B cell lymphoma A20 cells were transiently transfected with myc-tagged full-length protein of Abp1 (Abp1), Abp1 with its two tyrosine phosphorylation sites mutated (Y337FY347F), ABDs, and PRD and/or SH3 domains (PRD-SH3 and SH3) of Abp1. Twenty-four hours after transfection, cells were labeled with AF488 goat anti-mouse IgG for 20 min at 4°C and chased for 30 min at 37°C. Cells were fixed, permeabilized, and labeled with anti-myc Ab for myc-Abp1 and anti-LAMP-1 mAb for late endosomes. Arrows indicate cells expressing transfected proteins. Bar, 10 µm. B, Cells were categorized by visual inspection into three different categories, as described in Fig. 1. Shown are the average percentages (±SD) of cells in each of the three categories from three independent experiments. **, p < 0.01.