Phosphorylates a large number of substrates in the cytoplasm and the nucleus. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by cAMP. A number of inactive tetrameric holoenzymes are produced by the combination of homo- or heterodimers of the different regulatory subunits associated with two catalytic subunits. cAMP causes the dissociation of the inactive holoenzyme into a dimer of regulatory subunits bound to four cAMP and two free monomeric catalytic subunits. Testis specific. But important tissues such as brain and ovary have not been analyzed for the content of transcript. The disease is caused by variants affecting the gene represented in this entry. Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. cAMP subfamily. Extended N-terminus.