Tetramer, composed of 2 regulatory (R) and 2 catalytic (C) subunits. In the presence of cAMP it dissociates into 2 active monomeric C subunits and an R dimer that binds four cAMP molecules. Protein kinase activity is low in vegetative cells, rising sharply during sporulation; during germination its activity decreases to its original level. Belongs to the cAMP-dependent kinase regulatory chain family.