CLONING AND CHARACTERIZATION OF A GENE (UVR3) REQUIRED FOR PHOTOREPAIR OF 6-4-PHOTOPRODUCTS IN ARABIDOPSIS-THALIANA

UV radiation induces two major classes of pyrimidine dimers: the pyrim idine [6-4] pyrimidone photoproduct (6-4 product) and the cyclobutane pyrimidine dimer (CPD). Many organisms produce enzymes, termed photoly ases, that specifically bind to these damage products and split them v ia a UV-A/blue light-dependent mechanism, thereby reversing the damage , These photolyases are specific for either CPDs or 6-4 products, A ge ne that expresses a protein with 6-4 photolyase activity in vitro was recently cloned from Drosophila melanogaster and Xenopus laevis. We re port here the isolation of a homolog of this gene, cloned on the basis of sequence similarity, from the higher plant. Arabidopsis thaliana. This cloned gene produces a protein with 6-4 photolyase activity when expressed in Escherichia coil, We also find that a previously describe d mutant of Arabidopsis (uvr3) that is defective in photoreactivation of 6-4 products carries a nonsense mutation in this 6-4 photolyase hom olog. We have therefore termed this gene UVR3. Although homologs of th is gene have previously been shown to produce a functional 6-4 photoly ase when expressed in heterologous systems, this is the first demonstr ation of a requirement for this gene far photoreactivation of 6-4 prod ucts in vivo.