Genetic diversity of UV-sensitive DNA repair mutants of Chinese hamster ovary cells.

Abstract

Mutant lines of Chinese hamster ovary cells hypersensitivity to killing and mutagenesis by UV light were analyzed by genetic complementation analysis to determine whether defects in different gene loci might underlie a common cellular phenotype. To aid rapid screening of mutant clones, a procedure was devised that allowed presumptive complementation to be assessed on the basis of the frequency of UV-resistant cells after fusion by polyethylene glycol. Four classes were identified among 44 clones tested. By using drug-resistance markers for selection of hybrid cells in crosses between UV mutant and wild type, a mutant from each of the 4 classes was shown to be phenotypically recessive. Hybrids were isolated from crosses between each of the pair combinations of the 4 mutants. All such hybrids were relatively resistant to UV killing, providing confirmation of the complementation classes. When mutants representing the 4 UV-complementation classes were tested with the polyaromatic hydrocarbon 7-bromomethylbenz(a)anthracene, complementation was again seen for all pair combinations. Each class of mutants apparently represents a biochemical defect that plays a common role in the repair of both UV-induced and chemically induced lesions in the DNA.