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

Research Institute for Tuberculosis and Cancer, Tohoku University, 4-1 Seiryomachi, Aobaku, Sendai 980, [M. N., H. H., A. Y., A. O.]; Division of Genetics, National Institute of Radiological Science, 9-1, Anagawa-4-chome, Chiba-shi 260 [T. S.]; Division of Radiation Biology, Faculty of Pharmaceutical Science, Kanazawa University, Kanazawa 920, [T. Ma., O. N.]; and RI Center, Nara Medical University, Kashihara, Nara 634 [T. Mo.], Japan

UVS1 is an intermediately UV-sensitive Chinese hamster ovary mutant originally isolated by its hypersensitivity to an anticancer drug, 1-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-3-(2-chloroethyl)-3-nitrosourea 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 CHO9, the parental cell line, and 43-3B, a UV-hypersensitive 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 1-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-3-(2-chloroethyl)-3-nitrosourea 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 CHO9, suggesting that the gene products defective in UVS1 and 43-3B are essential for the excision repair of DNA damages produced by 1-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-3-(2-chloroethyl)-3-nitrosourea hydrochloride.

¹ To whom requests for reprints should be addressed.

Received 6/ 8/92. Accepted 11/10/92.