Photoactivatable fluorescent proteins (PAFPs) exhibit fluorescence that can be modified by a light-induced chemical reaction. Many PAFPs have been engineered from existing fluorescent proteins or
identified from large-scale screens in the wake of Kaede's discovery.
The classical PA-GFP converts from a non-radiant conformation to a GFP-like emitting fluorophore under UV excitation, while many of the other PAFPs undergo green-to-red photoconversions. Other colors
are available. Some proteins take part in irreversible photoconversion
reactions while other reactions can be reversed using light of a
specific wavelength.