Fig. 1. Confocal sections through nuclei show that AFT-complexes of AICD, Fe65 and Tip60 are localized to spherical nuclear spots. (A,B) Both AICD (yellow) and Fe65 (red) localized homogenously throughout nuclear (blue) and cytosolic compartments in transfected HEK293 cells. Co-expression of Fe65 and AICD resulted in the same localization. (C) In the absence of AICD and Fe65 co-expression, the histone acetylase Tip60 (cyan) localized to speckle-like nuclear structures. (D) In the absence of Fe65 co-expression, Tip60 had no effect on AICD distribution. (E) In the absence of AICD, Fe65 colocalized with Tip60 in nuclei and reorganized the speckle-like morphology into spherical nuclear spots. (F,G) In cells co-expressing AICD, Fe65 and Tip60, AICD was relocalized from the cytosol into AFT-complexes predominantly found in spherical nuclear spots. AFT-complexes were found throughout nuclei in all cells co-expressing the three proteins. Confocal xz sections of the same nuclei confirmed nuclear localization. (H) The NASA mutant of the putative Fe65-binding motif NKSY in Tip60 ineffectively localized some Fe65 and AICD to speckle-like nuclear structures, but completely abolished the formation of spherical nuclear spots. Bar, 10 µm.