UV radiation-sensitive Norin 1 rice contains defective cyclobutane pyrimidine dimer photolyase

Norin 1, a progenitor of many economically important Japanese rice strains, is highly sensitive to the damaging effects of UVB radiation (wavelengths 290 to 320 nm). Norin 1 seedlings are deficient in photorepair of cyclobuta ne pyrimidine dimers. However, the molecular origin of this deficiency was not known and, because rice photolyase genes have not been cloned and seque nced, could not be determined by examining photolyase structural genes or u pstream regulatory elements for mutations. We therefore used a photoflash a pproach, which showed that the deficiency in photorepair in vivo resulted f rom a functionally altered photolyase. These results were confirmed by stud ies with extracts, which showed that the Norin 1 photolyase-dimer complex w as highly thermolabile relative to the wild-type Sasanishiki photolyase. Th is deficiency results from a structure/function alteration of photolyase ra ther than of nonspecific repair, photolytic, or regulatory elements. Thus, the molecular origin of this plant DNA repair deficiency, resulting from a spontaneously occurring mutation to UV radiation sensitivity, is defective photolyase.