YPet is a yellow 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 F46L, I47L, F64L, R79K, M153T, V163A, S175G, S208F, V224L, H231E and D234N relative to YFP. YPet is optimized to act with CyPet as a cyan-yellow fluorescent protein pair for Forster resonance energy transfer (FRET), with YPet acting as the acceptor protein (PMID:15696158).