Fig. P1.

The application of TIRF and epifluorescence-structured light microscopy (TESM) reveals the presence of endosomes containing the protein Rabenosyn-5 in close apposition to clathrin-coated structures at the plasma membrane. The TfR, (yellow bars) moves from clathrin-coated structures (purple) into endosomes containing Rabenosyn-5 (green). Other early endosomes contain proteins such as EEA1 (red) and APPL (blue), but these endosomes do not accumulate TfR, demonstrating the specificity of Rabenosyn-5–containing endosomes in TfR trafficking. Depletion of Rabenosyn-5 results in TfR degradation, whereas depletion of EEA1 prevents degradation, suggesting that the role of endosomes containing Rabenosyn-5 is to direct TfR recycling to the plasma membrane, whereas endosomes containing EEA1 may direct trafficking to the degradative machinery of the cell.