GFP is a 27kD monomeric protein, which autocatalytically forms a fluorescent pigment. The wild type protein absorbs blue light (395nm) and emits green light (508nm) in the absence of additional proteins, substrates, or co-factors. Intact, native GFP protein is required for fluorescence. The GFP chromophore results from the cyclization and oxidation of the sequence Ser65-Tyr66-Gly67. GFP fluorescence is stable, species independent, and suitable for a variety of applications.