KillerRed is a red fluorescent protein with an excitation peak of 585nm and an emission peak of 610nm. It is an artificial derivative of the hydrozoan anm2CP gene (GenBank:AY485336), a non-fluorescent GFP-like chromoprotein. KillerRed acts as a genetically encoded photosensitizer; upon exposure to intense green light (540-580nm) it generates reactive oxygen species (both singlet oxygen and superoxide). This property can be used to selectively inactivate a protein of interest in living cells, using the chromophore-assisted light inactivation (CALI) technique; in this case KillerRed is fused to a protein of interest, and upon intense light illumination, the reactive oxygen species produced can disrupt the function of this protein by oxidizing susceptible amino acid residues (PMID:16369538). However, due to the tendency of KillerRed to dimerize, tagging of a protein of interest may interfere with its normal function, limiting its use as an experimental tool (PMID:17406328).