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

Having shown that gp210:HA is correctly sorted, we constructed a mutant cDNA coding for a protein that lacked both the TM and the CT, referred to as gp210-(TM + CT):HA (see Fig. 1 ). This protein showed a distribution characteristic of ER proteins (Fig. 3 B) and was no longer visible in the pore membrane, either when focusing on the nuclear surface (not shown), or when focusing on the nuclear rim (Fig. 3 B) . Double immunofluorescence with mAb 414 did show the characteristic punctate rim pattern of the nucleoporins (Fig. 3 A) . Likewise, a punctate nuclear rim staining pattern was seen with the anti-HA antibody in ceils expressing gp210:HA ( Fig. 3 C) . We conclude that the NH2-terminal ectoplasmic domain preceding the TM and comprising "~95% of gp210 lacks topogenic determinants for sorting to the pore membrane.