FIGURE 5.

Proteasome subunit, but not peptidase activity, is detected in purified nuclei. A, 20S proteasome subunit β7-GFP was expressed in HEK293T cells and detected uniformly throughout the cells (upper panels). Purified nuclei contained β7-GFP (lower panels). B, peptidase activity was measured in total (T), nuclear (N), and cytosolic (C) fractions using either equal protein concentration (conc.) or equal lysate volume (vol.), and results from three independent studies are shown (error bars indicate S.E.). C, protein lysates were resolved by SDS-PAGE and immunoblotted. The filters were reacted to antibodies against GFP and native β7. Whereas β7-GFP is detected in purified nuclei, native β7 was only present in the cytosol. A reaction against histone H3 is also shown.