cAMPr is a genetically encoded, single-wavelength fluorescent cAMP sensor. It consists of a full-length protein kinase A catalytic subunit (PKA-C), a PG linker, a circularly permuted form of GFP, a TAPPAC linker and amino acid residues 91 to 244 of a regulatory protein kinase A subunit (PKA-R). The PKA-R sequence lacks the dimerization/docking domain, preventing interaction with endogenous PKA subunits. Binding of cAMP to the PKA-R moiety elicits a conformational change that releases PKA-C from PKA-R and increases fluorescence without altering the excitation and emission spectra (which match those expected for GFP) (FBrf0238336).