ROCK1 polarizes Rac activity to the front of the cell. (A) Force diagrams and corresponding FRET ratiometric images for control and ROCK shRNA CHO.K1 cells plated overnight on fibronectin-coated 5-kPa polyacrylamide gels. (B) Quantification of Rac FRET at the front of the cell (180° from maximum) versus at the rear of the cell (0° = location of max force) for control and ROCK shRNA CHO.K1 cells. The constitutively active control, Raichu Rac V12, exhibits a uniform FRET signal throughout the cell, resulting in a ratio of ∼1. n = 6/8 control cells, 6/4 ROCK1 shRNA cells, and 7/7 ROCK2 shRNA cells, in which n = WT Raichu Rac/Raichu Rac V12. Error bars indicate SEM. Ctrl, control.