Fig. 5. Fluorescence loss in nucleoli upon bleaching in the nucleoplasm reveals dynamic distribution of NIK between nucleoli and nucleoplasm. FLIP experiments were performed with (A)YFP-NIK(1-769) and (B) YFP-NIK(1-794) as described in the Materials and Methods section. A bleach region was defined in the nucleoplasmic area, distant from nucleoli, and fluorescence intensities were measured in the nucleoplasm and in nucleoli over time. The decrease in nucleolar fluorescence indicates rapid exchange of nucleolar proteins with the nucleoplasm.