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

To determine whether the CT domain of CD8/gp(TM + CT) is required for sorting, we prepared a series of constructs where 10, 20, 30, 43, and 54 COOH-terminal residues of the 58-residue-long CT of the CD8/gp(TM + CT) were deleted (see Fig. 1 ). All of these proteins were correctly sorted to the pore membrane. Only the data for the CD8/gp(TM + CT)-20 and CD8/gp(TM + CT)-54 are shown (Fig. 5 ). Double immunofluorescence with both the anti-CD8 antibody and mAb 414 showed that the distribution of these chimeric proteins (Fig. 5 A and B) matched that of the nucleoporins (Fig. 5, C and D) . The 54-residue deletion removes nearly the entire CT leaving only four residues of the CT adjacent to the lipid bilayer. Data presented in the next section demonstrate that these four remaining residues are not sufficient for targeting to the pore membrane within the context of the CD8 TM (see Fig. 7 B) . Therefore, at most they play an accessory role in sorting. We thus conclude that the TM of gp210 is sufficient for pore membrane localization.