Figure 4.

Effects of leucine substitutions on K418 CD4 endocytosis and phosphorylation. (A and B) Endocytosis of K418 CD4 L substitutions (Figure 1) was measured as described in Figure 2A. Open symbols indicate the constitutive endocytosis of constructs in the absence of PMA, and solid symbols indicate endocytosis in the presence of 100 ng/ml PMA. (A) □ and ▪, K418; ○ and ●, K418 L413A/L414A; ⋄ and ♦, H399. (B) ▵ and ▴, K418 L413V/L414V; ○ and ●, K418 L413V. (C) Cells expressing K418 CD4 L413/L414 substitutions were labeled with [³²P]orthophosphate, incubated in medium with (+) or without (−) 100 ng/ml PMA for 3 min, and CD4 immunoprecipitated as described in Figure 2B. The left six lanes of the top panel were exposed to film for twice as long as the right six lanes.