Nuclear expression of Rac1 peaks in G2 in asynchronously dividing cells. PAE (A) or NIH 3T3 (B) cells stably expressing GFP-Rac1 at levels below endogenous were examined by time-lapse confocal microscopy over one division cycle. Arrowheads indicate representative parent and daughter cells. Note that nuclear Rac1 is high immediately preceding mitosis and that GFP-Rac1 is excluded from the nuclei of the daughter cells immediately after cell division. See Videos 1 and 2 . Bars, 10 μm.