Regulator of the myosin II component of the cytoskeleton: required for regulation of cytokinesis. Functions during chemotaxis, required for maintaining the direction of cell movement, suppressing lateral pseudopod extension, and proper retraction of the posterior of chemotaxing cells. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Cytosolic in unstimulated cells, localizes to the cytoskeleton in response to chemoattractant stimulation. Colocalizes with myosin II to the cleavage furrow of cells undergoing cytokinesis and the posterior cortex of polarized cells. Phosphorylation on Thr-585 results in cAMP-mediated activation and localization to the cytoskeleton. cells exhibit a defect in completing cytokinesis when grown in suspension, suggesting difficulties in regulating cytoskeletal organization required for cytokinesis, although karyokinesis is normal. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily.