Osmotic-sensitive mutants of Saccharomyces cerevisiae as screening organisms for promutagens and procarcinogens.

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Abstract
An attempt to improve the response of yeast cells to promutagens and procarcinogens in mutagenicity assay was made by using osmotic-sensitive mutants of a yeast, S. cerevisiae. Four osmotic-sensitive mutants of yeast which showed increased sensitivity to 1.5 M KCl were induced by ethylmethanesulfonate treatment. One of the mutants, strain C658-K42, was highly sensitive to antibiotics such as mitomycin C, novobiocin, nalidixic acid, chloroquine and rifampicin at concentrations showing no growth-inhibitory effect on the original strain, S. cerevisiae C658. Strain C658-K42 was considered to have a defect in the cell membrane. These osmotic-sensitive mutants were tested for suitability for screening by using well-known procarcinogens (promutagens), dimethylnitrosamine, 3,4-benzpyrene and 2-acetylaminofluorene. The response of these mutants in a mutagenicity assay (Trp+ reversion) was apparently increased compared with that of the original strain. The yeast cells which were harvested from a late logarithmic phase culture could activate procarcinogens to genetically active forms without any exogeneously added metabolic activation system.

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