The regulatory tandem domains of human phosphodiesterases 1 and 4 regulate a cyanobacterial adenylyl cyclase

► Tandem domains of phosphodiesterases 1 and 4 regulate adenylyl cyclase CyaB1. ► Regulation of CyaB1 by Ca2+/calmodulin with tandem domains from PDE1A3 and -B1. ► Regulation of CyaB1 by phosphomimetic mutation of UCR domains of PDE4A4, B1, D3. ► Mechanisms of intramolecular signaling in dimeric PDEs and adenylyl cyclases.