Fig. 6. Fusion of NoLS to fibrillarin makes it possible to delocalize fibrillarin from the DFC to the GC of nucleoli; this mislocalization of fibrillarin in the GC of nucleoli induces the mislocalization of the fibrillarin partner Nop56 in the GC but does not affect the localization of Nopp140. HeLa cells were cotransfected with fibrillarin-GFP and DsRed-B23 (a-d), with fibrillarin-NoLS-GFP and DsRed-B23 (e-h), with fibrillarin-GFP and DsRed-Nop56 (i-l), with fibrillarin-NoLS-GFP and DsRed-Nop56 (m-p), with fibrillarin-RFP and GFP-Nopp140 (q-t) or with fibrillarin-NoLS-RFP and GFP-Nopp140 (u-x). Fibrillarin (a) localized in the DFC of nucleoli, whereas B23 (b) localized preferentially in the GC as evidenced by the superimposition of both labelings (c) and by the comparison with the phase contrast image (d). When fused to NoLS, fibrillarin (e) was delocalized from the DFC to the GC of nucleoli and therefore colocalized with B23 (f) as evidenced by the superimposition of both labelings (g). Fibrillarin (i) colocalized with Nop56 (j) in the DFC of nucleoli as evidenced by the superimposition of both labelings (k). The delocalization of fibrillarin in the GC of nucleoli by the fusion of the NoLS (m) similarly modified the nucleolar localization of Nop56 (n), and therefore both proteins still colocalized as demonstrated by the superimposition of both labelings (o). Fibrillarin (q) and Nopp140 (r) colocalized in the DFC of nucleoli as evidenced by the superimposition of both labelings (s). By contrast to Nop56, the delocalization of fibrillarin fused to NoLS (u) did not modify the nucleolar localization of Nopp140 (v) as shown by the superimposition of both labelings (w). Bar, 10 µm.