Mutagenesis in S49 mouse lymphoma cells: induction of resistance to ouabain, 6-thioguanine, and dibutyryl cyclic AMP.

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The effects of mutagens on three genetic markers--resistance to ouabain, 6-thioguanine, and dibutyryl cyclic AMP (Bt2cAMP), were investigated in a mouse lymphoma cell line, S49. Nitrosoguanidine, ethyl methanesulfonate, ICR 191, and x-rays were used. Mutagen-specific responses were seen. Ouabain resistance was induced by nitrosoguanidine, but not by ICR 191. ICR 191 induced resistance to 6-thioguanine more efficiently than did nitrosoguanidine; the converse was true of resistance to Bt2cAMP. The relative frequency of biochemically distinguishable subtypes of mutants resistant to Bt2cAMP was characteristic of the mutagen used to generate them. The results can be interpreted as follows: nitrosoguanidine and ethyl methanesulfonate frequently, but ICR 191 and x-rays rarely, give rise to DNA base sequence changes that result in structurally altered but functional proteins. This type of change is required for induction of mutants resistant to ouabain and of certain classes of mutants resistant to Bt2cAMP. Resistance to 6-thioguanine and other classes of mutants resistant to Bt2cAMP can result from DNA base sequence changes that lead to extensive alteration of protein structure or expression; these changes are induced by ICR 191 or x-rays.

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