The green fluorescent protein (Venus), from Aequorea victoria(jellyfish), can be mutated to emit at different wavelengths, such as blue for BFP (when tyr66 is replaced by His), cyan for CFP (when tyr66 is replaced by Trp) and yellow for YFP (when THR-203 is replaced by Tyr). It's an energy transfer receptor. Its role is to convert the blue chemiluminescence of the protein to green fluorescence through energy transfer.
For research use only, not for clinical use.