Fig. 2. Changes in the large loop of UPIb do not interfere with exit from the ER. (A) Intact 293T cells expressing UPIa, Ib, Ib/a7, Ibm and IbCA were immunostained. In contrast to UPIa, all UPIb-related proteins are expressed on the cell surface. (B) Permeabilized 293T cells expressing UPIa, Ib, Ib/a7, Ibm and IbCA showed ER staining. (C,D) To locate the intracellular UP proteins, cells were cotransfected with the ER marker Ribophorin-I-GFP (RI-GFP) or the Golgi marker galactosyl transferase tagged with YFP (GalT-YFP) and then immunostained. The secondary antibody was conjugated to Texas Red. All the intracellularly retained UP chimeric proteins were colocalized with RI-GFP. Representative images of only UPIa and UPIb are shown here.