(A) Individual subunits of ATP-bound globular actin (G-actin) assemble into long filamentous polymers (F-actin), creating a double helix structure. Hydrolysis of the ATP destabilizes the polymer, causing dissolution of F-actin polymers into G-actin monomers. (B) ROCK stimulates stabilization of actin polymerization via an inhibitory phosphorylation of Lin11, Isl1, Mec3 (LIM) domain kinase (LIMK), which when active promotes ADP/cofilin-mediated actin severing.