Catalyzes the formation of the signaling molecule cAMP in response to G-protein signaling. ATP = 3',5'-cyclic AMP + diphosphate Binds 2 magnesium ions per subunit. Is also active with manganese (in vitro). Activated by forskolin. Insensitive to calcium/calmodulin. Stimulated by GNAS and by the G-protein beta and gamma subunit complex. The protein contains two modules with six transmembrane helices each; both are required for catalytic activity. Isolated N-terminal or C-terminal modules have no catalytic activity, but when they are brought together, enzyme activity is restored. The active site is at the interface of the two modules. Belongs to the adenylyl cyclase class-4/guanylyl cyclase family.