Green fluorescent protein (GFP) is a spontaneously fluorescent protein isolated from pacific jellyfish, Aequorea victoria. It transduces the blue chemiluminescence into green fluorescent light. Since the molecular cloning of GFP cDNA and demonstration of GFP as a functional transgene, GFP has become a powerful tool with exciting applications in developmental, cell and molecular biology. GFP fluorescence is not species specific and can be expressed in bacteria, yeast, plant and mammalian cells. GFP can fuse with proteins of interest without interfering significantly with their assembly and function.