Mount MCB 978125 Plants are constantly exposed to UV-B light from the sun and oxygen as a product of metabolism and both can and do damage DNA. Hence, plants are likely to utilize efficient mechanisms for repairing these types of DNA damage. Mutants of Arabidopsis that are abnormally sensitive to UV light have been isolated and found to comprise several complementation groups that map in different locations. Two genes, which have been tentatively identified as encoding products which are involved in the pathway for nucleotide excision repair of UV damage are under study. An attempt to positionally clone UVH1 and UVH3 is underway. Preliminary evidence suggests that the UVH1 locus may be a homolog of the human XP-B gene, a gene which is one of the several complementation groups involved in the human genetic disease xeroderma pigmentosum, as well as the yeast Rad 25 gene. The cloning of these genes will be completed, complementation tests performed and mutant genes sequenced. A radioimmune assay and complementation of the appropriate yeast mutants will further explore the function of the genes. The response to changing environmental conditions such as variation in UV light intensity and oxygen-production by the modification of transcriptional regulation will be investigated. Additional Arabidopsis excision repair genes will be identified, characterized and mapped. Plants can be expected to require highly efficient mechanisms for removal and repair of DNA damage since they are constantly exposed to sunlight and molecular oxygen, both factors known to cause DNA damage. Since the reproductive organs of plants are developmentally derived from undifferentiated somatic tissues, that task becomes even more critical in plants. Information derived from this on-going study will give greater insight into that repair process.
