Fig. 3. A C-terminal valine acts as a transport signal. (A) A schematic representation of CD4 reporter constructs. CD4 represents the luminal domain possessing two N-glycosylation sites; L₁₈ represents 18 leucine TMD and X indicates mutated residues. (B) Effect of motifs at XX positions. COS cells were transfected with the indicated constructs, pulse-labeled with [³⁵S]-methionine, chased for 60 minutes and subjected to immunoprecipitation with anti-CD4. Immunoprecipitates were digested with endo H (+) or left untreated (-), separated by SDS-PAGE and visualized by fluorography. The upper band in the endo H+ lanes is the endo-H-resistant and the lower band to the endo-H-sensitive form of the CD4 reporter. (C) Quantification of fluorograms. Means±s.e.m. of at least three independent experiments. Asterisk, difference to the AA values is statistically significant (student's t-test, P<0.05).