Enhanced cell permeability increases the sensitivity of a yeast test for mutagens

tauthor is a mutation which causes a general increase in permeability of Sacharomyces cerevisiae cells in an unspecific manner. The introduction of the tauthor mutation under homozygous conditions into the D7 diploid strain enhanced the sensitivity of the test system described by Zimmermann et al. (1975). The newly constructed strain D7tauthor responded with a four to six times higher frequency compared to the D7 strain for all genetic end-points induced with chemical mutagens (ethyl methanesulfonate, methyl methanesulfonate, hydroxyurea, benzpyrene). The increased sensitivity of D7tauthor is specific only for mutagens active in yeast, since treatment of D7tauthor cells with 5-bromouracil or 5-bromouridine, known to be non-mutagenic in yeast, did not result in the induction of any of the measured genetic alterations. Five out of 14 water samples taken from the environment induced recombinogenic events in D7tauthor, whereas all 14 water samples were without effect in the D7 test system. We concluded that D7tauthor cells show a higher sensitivity in the detection of mutagenic or carcinogenic action because of their generally enhanced permeability due to the tauthor mutation.