T-Epac-VV is a genetically encoded fluorescent cAMP sensor. It is a fusion protein that consists of a FRET (fluorescence resonance energy transfer) donor (mTurquoise with a truncation of the C-terminal 11 amino acids) and a FRET acceptor (Venus and a circular permutation of Venus in tandem) which are separated by part of the Homo sapiens RAPGEF3 cAMP-binding protein. The RAPGEF3 portion undergoes a conformational change upon binding to cAMP, which causes a robust decrease in FRET (PMID:21559477).