Fig. 4. R-rings are distinct from the nuclear envelope but contain an ER-specific membrane protein. Double immunofluorescence of HA-NoppR-transfected COS cells stained for the inner nuclear membrane protein, LAP2 (a), the nuclear pore complex protein, p62 (b), the nuclear lamina protein, lamin B (c) and the ER transmembrane protein, calnexin (d). To identify the R-rings, the cells were double labeled with HA-antibodies for the transfected HA-NoppR (a’-d’) and imaged by phase contrast (a"-d"). One R-ring is pointed out (arrow). Bar, 10 µm.