Required for cAMP-mediated activation of guanylyl cyclase activity and plays an essential role in aggregation, morphogenesis, and chemotaxis. Appears to act upstream of erk1 but not erk2. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Interacts with mip1. Predominantly nuclear in vegetatively growing cells. Translocates to the cell cortex in response to chemoattractant stimulation and is present at the leading edge of chemotaxing cells. Sumoylated and ubiquitinated in response to chemoattractant stimulation. Sumoylation is linked to kinase activation and results in translocation. Cells are unable to undergo chemotaxis properly during aggregation in response to the chemoattractant cAMP or activate guanylyl cyclase. Form extremely small aggregates resulting in the development of slugs and terminal fruiting bodies that are significantly smaller than those of wild-type cells. Transfer of the temperature-sensitive mutants from a temperature of 18 degrees Celsius to 27 degrees Celsius causes forming aggregates to split into multiple small aggregates. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.