FLAVIN ADENINE-DINUCLEOTIDE AS A CHROMOPHORE OF THE XENOPUS (6-4)PHOTOLYASE

Two types of enzyme utilizing light from the blue and near-UV spectral range (320-520 nm) are known to have related primary structures: DNA photolyase, which repairs UV-induced DNA damage in a light-dependent m anner, and the blue light photoreceptor of plants, which mediates ligh t-dependent regulation of seedling development. Cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts [(6-4)pho toproducts] are the two major photoproducts produced in DNA by UV irra diation. Two types of photolyases have been identified, one specific f or CPDs (CPD photolyase) and another specific for (6-4)photoproducts [ (6-4)photolyase]. (6-4)Photolyase activity was first found in Drosophi la melanogaster and to date this gene has been cloned only from this o rganism. The deduced amino acid sequence of the cloned gene shows that (6-4)photolyase is a member of the CPD photolyase/blue light photorec eptor family. Both CPD photolyase and blue light photoreceptor are fla voproteins and bound flavin adenine dinucleotides (FADs) are essential for their catalytic activity. Here we report isolation of a Xenopus l aevis (6-4)photolyase gene and show that the (6-4)photolyase binds non covalently to stoichiometric amounts of FAD. This is the first indicat ion of FAD as the chromophore of (6-4)photolyase.