Figure 7.

Tyrosine-based and acidic cluster signals utilize distinct saturable components for internalization from the plasma membrane. HeLa cells were transiently transfected with 20 μg of plasmid encoding Tac, TTMb (upper panel), or TacF766–93 (lower panel). After 40 h, cells were harvested, stained on ice with phycoerythrin-anti-Tac and fluorescein-antiCD63, and analyzed by flow cytometry. Inset, dot plot showing phycoerythrin staining (anti-Tac) on the y-axis and fluorescein staining (anti-CD63) on the x-axis for cells transfected with TTMb or TacF766–93. Each dot represents a single counted cell. Main graph, The dark line indicates CD63 staining on cells gated for surface expression above background for either TTMb or TacF766–93. The thin lines show CD63 staining on cells expressing similar levels of the noninternalized Tac. This level of staining is identical to that obtained with untransfected cells and likely represents the steady state expression level of CD63 under nonsaturating, physiological conditions. The dotted lines represent staining with a nonspecific control antibody (anti-CD4-FITC).