||Analysis of Trifluorothymidine-Resistant (TFT(sup r)) Mutants of L5178Y/TK(sup +/-) Mouse Lymphoma Cells.
Moore, M. M. ;
Clive, D. ;
Hozier, J. C. ;
Howard, B. E. ;
Batson, A. G. ;
||Health Effects Research Lab., Research Triangle Park, NC. ;Burroughs Wellcome Co., Research Triangle Park, NC. ;Florida Inst. of Tech., Melbourne.
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Three classes of TFTr variants of L5178Y/TK+/- -3.72C mouse lymphoma cells can be identified - large colony (lambda), small colony (sigma),and tiny colony (tau). The sigma and lambda mutants are detectable in the routine mutagenesis assay using soft agar cloning. The tau mutants are extremely slow growing and are quantified only in suspension cloning in microwells. Variants of all three classes have been analyzed in the process of evaluating the usefulness of the thymidine kinase locus in L5178Y/TK +/- mouse lymphoma cells for detecting induced mutational damage. 150 of 152 variants from mutagen treated cultures and 163 of 168 spontaneous mutants were TFTr when rechallenged approximately 1 week after isolation (3 weeks after induction). All of the 41 mutants assayed for enzyme activity were TK-deficient. The sigma and tau phenotypes were found to correlate with slow cellular growth rates (doubling time > 12 h), rather than from effects of the TFT selection or mutagen toxicity. Cytogenetic analysis of sigma mutants approximately 3 weeks after induction shows an association between the sigma phenotype and readily observable (at the 230-300 band level) chromosomal abnormalities (primarily translocations involving that chromosome 11 carrying the functional TK gene) in 30 of 51 induced mutants studied.