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. RFP is the recent discovered protein that has the similar function and applications as GFP. Either GFP or RFP fluorescence is not species specific and can be expressed in bacteria, yeast, plant and mammalian cells. GFP or RFP can fuse with proteins of interest without interfering significantly with their assembly and function.