Photorepair mutants of Arabidopsis

UV radiation induces two major DNA damage products, the cyclobutane pyrimidine dimer (CPD) and, at a lower frequency, the pyrimidine (6–4) pyrimidinone dimer (6–4 product). AlthoughEscherichia coli andSaccharomyces cerevisiae produce a CPD-specific photolyase that eliminates only this class of dimer,Arabidopsis thaliana ,Drosophila melanogaster ,Crotalus atrox , andXenopus laevis have recently been shown to photoreactivate both CPDs and 6–4 products. We describe the isolation and characterization of two new classes of mutants ofArabidopsis , termeduvr2 anduvr3 , that are defective in the photoreactivation of CPDs and 6–4 products, respectively. We demonstrate that the CPD photolyase mutation is genetically linked to a DNA sequence encoding a type II (metazoan) CPD photolyase. In addition, we are able to generate plants in which only CPDs or 6–4 products are photoreactivated in the nuclear genome by exposing these mutants to UV light and then allowing them to repair one or the other class of dimers. This provides us with a unique opportunity to study the biological consequences of each of these two major UV-induced photoproducts in an intact living system.