Fig. 2. Giant endosomes kinetically correspond to both early and late endosomes. To determine the nature of the large endosomes, control or rab5(Q79L)-expressing cells were allowed to internalize the fluid phase endocytic tracer BSA-rhodamine (1.5 mg/ml) for 2 minutes, followed by the indicated times of chase. While BSA-rhodamine was observed in small vesicles (small arrows) at each time point studied in control cells, in mutant cells this tracer was present in giant endosomes (large arrows) for at least 30 minutes after its internalization. However, chase of the fluorescent tracer for 60 minutes resulted in its transfer to smaller vesicles similar to those observed in control cells. The inset represents large vacuoles (arrowheads) not displaying the fluorescent tracer that could be observed at this time point in rab5(Q79L)-expressing cells. n, nucleus. Bar, 10 µm.

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