Shimomura proteolyzed denatured GFP, analyzed the peptide that retained visible absorbance, and correctly proposed that the chromophore is a 4-(p-hydroxybenzylidene)imidazolidin-5-one attached to the peptide backbone through the 1- and 2-positions of the ring. Aequorea and Renilla GFPs were later shown to have the same chromophore (7); and the pH sensitivity, aggregation tendency (8), and renaturation (9) of Aequorea GFP were characterized. But the crucial breakthroughs came with the cloning of the gene by Prasher et al (10) and the demonstrations by Chalfie et al (11) and Inouye & Tsuji (12) that expression of the gene in other organisms creates fluorescence. Therefore the gene contains all the information necessary for the posttranslational synthesis of the chromophore, and no jellyfish-specific enzymes are needed.