Fig. 1. R-rings are membranous structures. Fluorescence of COS cells transfected with the HA-tagged full-length Nopp140 (HA-Nopp140) (a and b) or the Nopp140 repeat domain (c). The cells were stained for the transfected protein with HA-antibodies (a,b) or for membranes with the lipophilic dye, DiOC₆ (c). Note the varied appearance of the R-rings in different cells by indirect immunofluorescence (a,b) and by phase contrast microscopy (a’-c’). Two R-rings are pointed out in each panel (arrows). Note that the phase dense particles of the R-rings (arrows in a’ and c’) are distinct from nucleoli (asterisks). An overlay of the fluorescence with the phase contrast images shows the location of the R-rings in the nucleoplasm and in the nucleoli (a"-c"). Bar, 10 µm.