Nuclear Rac1 is prenylated. (A) Nuclear and nonnuclear fractions were prepared as described in Materials and methods. After separation, each fraction was brought to 1% Triton X-114 and phase separation was initiated by heating the samples to 37°C. The aqueous and detergent phases of each fraction were analyzed for Rac1, RhoGDI, and lamin B by immunoblotting. Immunoblots were quantified with [125I]protein A and phosphorimaging, and the percentage of total protein in each fraction in the detergent phase was calculated (mean ± SEM; n = 3). (B) Triton X-114 partition as shown in A was performed on the nuclear fractions of COS-1 cells treated overnight with or without 10 μM simvistatin. Aq, aqueous; Det, detergent phases. (C) Selected images of GFP-Rac1 in COS-1 and ECV cells showing prominent decoration of the nuclear envelope (arrowhead). Bars, 10 μm.