Emerald is a monomeric green fluorescent protein (PMID:20664080) with an excitation peak of 487nm and an emission peak of 509nm in vitro (PMID:9759496). It is an artificial derivative of the naturally occurring fluorescent protein encoded by the Aequorea victoria GFP gene (UniProtKB:P42212), containing the mutations S65T, S72A, N149K, M153T and I167T (PMID:9759496).