Has role in the regulation of chemotaxis. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Kinase activity is rapidly and transiently increased in response to chemoattractant stimulation. Interacts with GTP-bound racB. Cytosolic in unstimulated cells, localizes to the plasma membrane in response to chemoattractant stimulation with kinetics consistent with those of kinase activation, where it binds to phospholipids via its PH domain. Preferentially expressed during vegetative growth and in the earliest stages of development. Expressed at significantly lower levels during later stages of development. Cells are less-polarized than wild-type and are unable to properly regulate the direction of pseudopod formation, resulting in a reduction in the distance traveled in response to chemoattractant. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily.