||Molecular Dissection of Mutations at the Heterozygous Thymidine Kinase Locus in Mouse Lymphoma Cells.
Applegate, M. L. ;
Moore, M. M. ;
Broder, C. B. ;
Burrell, A. ;
Hozier, J. C. ;
||Florida State Univ., Tallahassee. Dept. of Biological Science. ;Florida Inst. of Tech., Melbourne. Dept. of Biological Science. ;Yale Univ., New Haven, CT. Dept. of Biology. ;IBM Research Div., San Jose, CA.;Health Effects Research Lab., Research Triangle Park, NC.
Thymidine kinase ;
Chromosome mapping ;
Restriction fragment length polymorphism ;
Cultured tumor cells ;
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The mouse lymphoma L5178Y TK+/- 3.7.2C cell line allows quantitation of induced TK +/- -> TK-/- mutations at the heterozygous thymidine kinase (tk) locus. TK-/- mutant colonies show a bimodal size distribution, reflecting a difference in the growth rates of the two size classes that is hypothesized to result from different degrees of genetic damage. The two homologous chromosomes containing the alleles of the tk gene in L5178Y 3.7.2C TK+/- cells are distinguishable at the cytogenetic level by the unique centromeric morphology of each of the two chromosomes 11, to which the tk gene has been mapped in mouse cells. In addition, the two alleles were distinguishable at the molecular level because of an Nco I restriction-fragment-length polymorphism at the 3' end of the gene. In a set of 51 large-colony and 48 small-colony TK-/- mutants induced by ionizing radiation or by chemical mutagens, 78, including all except one of the small-colony mutants, have lost the tk+ allele and that some of these have two to four copies of the remaining, tk-, allele. Nineteen of the large-colony TK-/- mutants that do not show tk+ allele loss show no other structural changes detectable at the level of Southern blot analysis.