May play a role in responding to changes in chemoattractant levels. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Mutants have an aberrant response to waves of cAMP stimulation. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily.