The GDP/GTP cycle of Rab5 in the regulation of endocytotic membrane traffic

In eukaryotic cells, endocytosis plays a central role in the maintenance of cellular organization and func-tion. The endocytotic route is composed of separate stations that carry out specialized functions uch as up-take of nutrients, clearance of metabolites from the medium, internalization and down-regulation f recep-tors, turnover of membranes, and antigen processing. Proteins, lipids, and solutes internalized at the cell sur-face are first transported into early endosomes. The best-characterized route to this compartment is the clathrin-coated-vesicles-mediated route (Robinson 1994), but non-clathrin-mediated mechanisms also con-tribute to the endocytotic traffic (Watts and Marsh 1992; Sandvig and van Deurs 1994). From the early endosomes, internalized constituents can be eithe