The single transmembrane segment of gp210 is sufficient for sorting to the pore membrane domain of the nuclear envelope

Our observation that a fraction of gp210 co-localizes with the eytoplasmically dispersed, mAb 414-reactive nucleoporins suggests that these components are associated with each other, perhaps in annulate lamellae. These structures are likely to represent excess pore membrane and pore complex components. Mutant gp210 appeared to be sorted to these Figure 7 . A 20-amino acid residue deletion from the COOH-terminal tail of the CD8/gpCT chimera abolishes NE localization. 3T3 cells expressing CD8/gpCT (A) or the deletion mutant CD8/gpCT-20 (B) were fixed, permeabilized, and probed with anti-CD8 antibody. Binding was visualized with Texas red-labeled goat anti-mouse IgG. The focal plane shown reveals the cell surface adjacent to the coverslip. Note that both chimeric proteins are visible at the cell surface (A and B), but the punctate NE staining pattern seen with CD8/gpCT (A) is absent in the CD8/gpCT-20 expressing cell (B). Bar, 10 #m. cytoplasmic structures as long as they are also sorted to the pore membrane domain of the NE (see Figs. 2, 4, and 5). It therefore seems likely that sorting of gp210 to a pore membrane domain in the ER occurs by the same principles as sorting to the pore membrane domain of the NE.