ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Autophosphorylated on serine and threonine residues. Dephosphorylated by PstP (By similarity). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.