NowGFP is a monomeric fluorescent protein that shows bright green fluorescence at physiological and higher pH and weak cyan fluorescence at low pH. The green fluorescent form has an excitation peak of 494nm and an emission peak of 502nm. At basic and neutral pH, illumination with blue light (450-480nm) results in almost irreversible photoconversion from the green to the cyan form (limited recovery of the green form is seen when illumination ceases). NowGFP is an artificial derivative of the naturally occurring fluorescent protein encoded by the Aequorea victoria GFP gene (UniProtKB:P42212) (FBrf0229094, PMID:26249350).