Large-scale isolation of UV-sensitive clones of CHO cells.

We have isolated 54 ultraviolet light (UV) sensitive clones of Chinese hamster ovary (CHO) cells, including two from a parent cell line which is hypersensitive to ethyl methanesulfonate (EMS) and is also sensitive to X rays. A replica plating technique was used for the isolation of two of the clones, and a semiautomated technique was used for the isolation of the other 52 clones. We have observed UV sensitization of up to 5-fold in the mutants relative to the parent in terms of the slopes of the survival curves. Seven of the clones were examined for DNA repair competence using a repair replication assay, and all exhibited a DNA repair defect resembling that seen in human mutant xeroderma pigmentosum cells. We have also demonstrated an approximately 9-fold enhancement in the UV mutagenic response of two of the repair replication-defective clones relative to the parent for resistance to ouabain, 6-thioguanine, and 8-azaadenine.