Twenty copies of the UAS regulatory sequence drive expression of two different fluorophores (CFP and YFP) which are separated by sequences encoding only the cAMP-binding domain of the Homo sapiens RAPGEF3 gene. When not bound to cAMP, Avic\GFPEpac1-camps.20xUAS supports fluorescence resonance energy transfer (FRET) from CFP to YFP. The binding of cAMP forces the CFP and YFP domains to move apart leading to a reduction in FRET levels when cAMP levels rise.