ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Expressed throughout development, high during embryonic and adult stages. Isoform T2 is predominantly expressed during larval and adult stages. Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. cGMP subfamily.