Use of a Highly Sensitive Assay to Analyze the Excision Repair of Dimer and Nondimer DMA Damages Induced in Human Skin Fibroblasts by 254-nm and Solar Ultraviolet Radiation1

The excision repair of nondimer DNA damages induced in normal human skin fibroblasts exposed to the Mylar-filtered UV produced by a fluorescent sunlamp was investigated. This work was accomplished through the development of a modification of the bromodeoxyuridine photolysis assay that greatly increases the sensitivity of this assay. This enhancement in sensitivity was achieved through use of alkaline elution to measure the DNA strand breakage produced by the photolysis of bromodeoxyuri dine incorporated into the DNA through excision repair. Using this modified bromodeoxyuridine photolysis assay, it was found that the solar UV-induced nondimer DNA damages appear to have been repaired by a short patch repair mechanism in which a small number of nudeotides (two to four) were inserted into the repaired site. This is in contrast to the long patch repair process involved in the excision of cyclobutane pyrimidine dimers in which approximately 40 nudeotides were inserted into each repaired region.