PHOTOREPAIR MUTANTS OF ARABIDOPSIS

UV radiation induces two major DNA damage products, the cyclobutane py rimidine dimer (CPD) and, at a lower frequency, the pyrimidine (6-4) p yrimidinone dimer (6-4 product). Although Escherichia coli and Sacchar omyces cerevisiae produce a CPD-specific photolyase that eliminates on ly this class of dimer, Arabidopsis thaliana, Drosophila melanogaster, Crotalus atrox, and Xenopus laevis have recently been shown to photor eactivate both CPDs and 6-4 products. We describe the isolation and ch aracterization of two new classes of mutants of Arabidopsis, termed uv r2 and uvr3, that are defective in the photoreactivation of CPDs and 6 -4 products, respectively. We demonstrate that the CPD photolyase muta tion is genetically linked to a DNA sequence encoding a type II (metaz oan) CPD photolyase. In addition, we are able to generate plants in wh ich only CPDs or 6-4 products are photoreactivated in the nuclear geno me by exposing these mutants to UV light and then allowing them to rep air one or the other class of dimers. This provides us with a unique o pportunity to study the biological consequences of each of these two m ajor UV-induced photoproducts in an intact living system.