Identification of Cellular Defect in UVS1, a UV-sensitive Chinese Hamster Ovary Mutant Cell Line

UVS1 is an intermediately UV-sensitive Chinese hamster ovary mutant originally isolated by its hypersensitivity to an anticancer drug, l-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-3 hydrochloride. By cell fusion analysis, UVS1 complemented the UV sensitivity of the mouse lymphoma cell line US31 from the eighth complementation group of UV-sensitive rodent cell lines. By enzyme-linked immunosorbent assay we found that within 3 h after UV irradiation both pyrimidine dimers and (6-4)photoproducts in UVS1 were not removed from chromosomal DNA in UVS1 at all. Twenty-four h after UV irradiation the removal rate of (6-4)photoproducts was intermediate between CH09, the parental cell line, and 43-3B, a UV-hypersensiUve Chinese hamster ovary mutant of the complementation group 1, whereas the pyrimidine dimers in UVS1 were removed less efficiently as 43-3B. Alkaline elution assay showed that the incising activity to damaged DNA after UV irradiation of UVS1 was as low as that of 43-3B. The number of l-[(4-amino-2-methyl-5-pyrimidinyl)methyl- hydrochloride-induced DNA Interstrand cross-links of UVS1 was almost equal to that of 43-3B and about 1.5 times more than that of CH09, suggesting that the gene products defective in UVS1 and 43-3B are essential for the excision repair of DNA damages produced by l-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-3-(2-chloroethyl)-3-nitrosourea hydrochloride.