title: Isolation of Chinese hamster cell mutants deficient in dihydrofolate reductase activity.
abstract: Mutants of Chinese hamster ovary cells lacking dihydrofolate reductase (tetrahydrofolate dehydrogenase, 7,8-dihydrofolate:NADP+ oxidoreductase; EC 1.5.1.3) activity were isolated after mutagenesis and exposure to high-specific-activity [3H]deoxyuridine as a selective agent. Fully deficient mutants could not be isolated starting with wild-type cells, but could readily be selected from a putative heterozygote that contains half of the wild-type level of dihydrofolate reductase activity. The heterozygote itself was selected from wild-type cells by using [3H]deoxyuridine together with methotrexate to reduce intracellular dihydrofolate reductase activity. Fully deficient mutants require glycine, a purine, and thymidine for growth; this phenotype is recessive to wild type in cell hybrids. Revertants have been isolated, one of which produces a heat-labile dihydrofolate reductase activity. These mutants may be useful for metabolic studies relating to cancer chemotherapy and for fine-structure genetic mapping of mutations by using available molecular probes for this gene.
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D006579:Heterozygote; D006822:Hybrid Cells / Q000201:enzymology; D009154:Mutation; D010053:Ovary; D012641:Selection, Genetic; D013762:Tetrahydrofolate Dehydrogenase / Q000172:deficiency* / Q000235:genetics
chemical_list: D013762:Tetrahydrofolate Dehydrogenase