Figure 5. Tapasin Δ334-342, but not soluble tapasin, enhances the surface expression of D^b and K^b molecules.

(A) Folded D^b and K^b molecules were immunoprecipitated from cell equivalents with the B22/249 and Y3 mAbs, respectively. The immunoprecipitated proteins were electrophoresed on 4→20% acrylamide Tris-glycine gels, transferred to membranes, and probed on western blots with rabbit anti-K^b serum or rabbit anti-D^b serum. In the D^b blot, an additional band (marked with an asterisk) with slower migration is found in the MF-K^d-WT and MF-K^d-ΔTsn cell lines. This band presumably represents MHC class I molecules that are mature glycoproteins. Mature K^b molecules are also likely to be present in the MF-K^d-WT and MF-K^d-ΔTsn cell lines; however, the K^b bands did not resolve as well. Noncontiguous lanes from the same gel are indicated by a dashed line. The finding of less folded D^b and K^b in MF-K^d-SOL-ΔTsn than in MF-K^d-WT, as shown, is representative of data from two experiments. (B) Cell surface expression of folded D^b and K^b molecules on the indicated cell lines was determined by flow cytometry using the B22/249 and Y3 mAbs, respectively.