Epac1-camps is a genetically encoded fluorescent cAMP sensor. It is a fusion protein composed of two different fluorophores (EYFP and ECFP) that are separated by the cAMP-binding domain of the Homo sapiens RAPGEF3 gene (HGNC:16629). When not bound to cAMP, fluorescence resonance energy transfer (FRET) from ECFP to EYFP is supported. The binding of cAMP forces the ECFP and EYFP domains to move apart, leading to a reduction in FRET levels when cAMP levels rise (PMID:15231839).