Figure 2.

Immature thymocytes express ER-resident proteins, including molecular chaperones, on the cell surface. Thymic lymphoma cells were proteolyzed and then cultured in medium alone, medium containing 1 μg/ml BFA, or medium containing 10 μg/ml of the protein synthesis inhibitor CHX. After biotin surface-labeling of cells, digitonin cell extracts were immunoprecipitated with Ab specific for (A) CRT, (B) KDEL, (C) rI, rII, and signal sequence receptor α. It should be appreciated that the anti-KDEL Ab was originally generated by immunization with peptides encompassing the retention signal of BiP and does not recognize all KDEL-containing ER proteins equally.