CyPet is a cyan fluorescent protein. It is an artificial derivative of the naturally occurring fluorescent protein encoded by the Aequorea victoria GFP gene (UniProtKB:P42212), containing the mutations T9G, V11I, D19E, A87V, I167A, E172T and L194I relative to ECFP. CyPet and YPet act as an optimized cyan-yellow fluorescent protein pair for Forster resonance energy transfer (FRET), with CyPet acting as the donor protein (PMID:15696158).