Cloning of Drosophila gene which code for UV-damaged DNA binding protein

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Cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts ((6-4) photoproducts) are the two major classes of cytotoxic mutagenic and carcinogenic DNA photoproducts produced by ultraviolet light irradiation of cells. The phenomenon of photoreactivation, the reduction of the lethal and mutagenic effects of ultraviolet radiation by simultaneous or subsequent irradiation with near ultraviolet or visible light, has been identified in several organisms and in some cases the enzymes that catalyze this process have been characterized in sufficient detail. CPDs are the only known substrate for the photoreactivating enzymes so far analyzed and enzymatic photoreactivation of (6-4) photoproducts has not yet been reported.Using gel shift assay we have identified two protein factors (Factor 1 and Factor 2) which bind specifically to UV-irradiated DNA. After purification we have determined the enzymatic activity of each factor.Factor 2 is a Drosophila homologue of photolyase (which photoreactivate CPDs). Factor 1 is a photoreactivating enzyme of (6-4) photoproduct. This is the first report of such photoreactivating activity specific for (6-4) photoproduct in any organism.