Figure 5.

Effects of serine substitutions on K418 CD4 endocytosis and phosphorylation. (A and B) Endocytosis of K418 CD4 S to A substitutions (Figure 1) was measured as described in Figure 2A. (A) Constitutive endocytosis of the constructs in the absence of PMA. (B) Endocytosis in the presence of 100 ng/ml PMA. □ and ▪, K418; ○ and ●, K418 S408A; ▿ and ▾, K418 S415A; ▵ and ▴, K418 S408A/S415A; ⋄ and ♦, H399. (C) Cells expressing K418 CD4 S to A or E (see Figure 5) substitutions were labeled with [³²P]orthophosphate, incubated in medium with (+) or without (−) PMA, and CD4 immunoprecipitated as described in Figure 2B.