FIG. 6.

Model for the interference of Vpu with cell surface expression of BST-2. BST-2 expressed at the cell surface is not static but cycles between the endocytic compartment and the cell surface (1). The majority of internalized BST-2 (as indicated by the size of the arrowhead) is recycled to the cell surface (2). A small fraction of internalized BST-2 molecules is not recycled to the surface but remains inside the cell and is targeted for degradation in the lysosomal compartment (3). The BST-2 population at the cell surface is maintained at constant levels by replacing the nonrecycled portion of BST-2 with de novo-synthesized protein from the endoplasmic reticulum (ER) (4). The interference of Vpu with the resupply (5) results in the gradual depletion of cell surface BST-2.