Expression of CRP1 increases the bundling of cellular actin filaments. REFs transfected with pECFP-CRP1 as described in Experimental Procedures were lysed and the Triton X-100 soluble and insoluble fractions separated for analysis. The transfection conditions were: 1) 6 μL FuGENE, no DNA; 2) 3 μL FuGENE, 0.5 μg DNA; 3) 3 μL FuGENE, 1.0 μg DNA; 4) 6 μL FuGENE, 1.0 μg DNA; and 5) 6 μL FuGENE, 2.0 μg DNA. Immunoblot shows the expression of CFP-CRP1 in each fraction (A). REFs transfected with pECFP-CRP1 using transfection condition 4 were fixed and prepared for fluorescence microscopy. Rhodamine-phalloidin staining of F-actin (A, B, C) shows that the cells expressing CFP-CRP1 (A', B', C') have enlarged stress fibers (see arrows). Results are representative of 4 separate experiments. Bar = 10 μm.