title: Derivation of TK- clones from revertant TK+ mammalian cells.
abstract: In order to obtain a large collection of Chinese hamster cell clones defective in thymidine kinase (TK(-)), BrdU(r) selection experiments have been performed on wild-type and revertant TK(+) cell lines. No clones (< 10(-9)) were obtained from the wild-type TK(+) cell line by single-step selection. In contrast, revertant TK(+) clones readily gave rise to stable TK(-) derivatives (1 - 2 x 10(-4)). Both wild-type and revertant TK(+) clones spontaneously yielded 8-AG(r) colonies with the same frequency (1 - 5 x 10(-6)), suggesting that the differences between wild-type and revertant cell lines specifically affected selection of the TK(-) phenotype. The increased frequency of TK(-) clones reflects perhaps the number (ploidy) or character of the autosomal TK loci in TK(+) revertants, or perhaps the mechanisms which regulate expression of the TK genes. Several mutagens, EMS, MNNG and UV, stimulated the TK(+) revertants' frequency of TK(-) subclones only slightly (< 3-fold). Biochemical and genetic data indicated that the TK(-) clones derived from one revertant are phenotypically different. The phenotypes displayed by these cell lines are stable and do not depend upon the continued presence of the selective agent.
mesh_terms: D001973:Bromodeoxyuridine; D002250:Carbon Radioisotopes; D002460:Cell Line; D002999:Clone Cells; D004351:Drug Resistance; D005069:Evaluation Studies as Topic; D007621:Karyotyping; D008168:Lung / Q000201:enzymology / Q000528:radiation effects; D008698:Mesylates; D008722:Methods; D009153:Mutagens; D009154:Mutation; D009574:Nitro Compounds; D009604:Nitrosoguanidines; D010641:Phenotype; D011831:Radiation Genetics; D012641:Selection, Genetic; D013936:Thymidine; D013937:Thymidine Kinase / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D002250:Carbon Radioisotopes; D008698:Mesylates; D009153:Mutagens; D009574:Nitro Compounds; D009604:Nitrosoguanidines; D013937:Thymidine Kinase; D001973:Bromodeoxyuridine; D013936:Thymidine