Figure 4.

Nuclear import of cyclin B1–Cdc2 is not blocked by dominant negative importin β. Nuclear import reactions were performed with interphase cytosol and cyclin B1E–Cdc2K⁻ (A and B), wild-type cyclin B1–Cdc2 (C and D), or FITC-NLS-BSA (E and F), in the absence of inhibitor (A, C, and E) or in the presence of 2 μM importin β-(71–876) (B, D, and F). Because importin β-(71–876) is Myc-tagged, cyclin B1 in this experiment was detected with monoclonal anti-cyclin B1 antibodies. Endogenous cyclin B1 is not present at significant levels in the permeabilized cells and cytosol used in these experiments (data not shown).