Dominant mutation for ethionine resistance in Saccharomyces cerevisae.

An ethionine-resistant mutant of Saccharomyces cerevisiae has been investigated whose mutation (et(r2)) confers resistance to the heterozygous diploid also containing the sensitive allele, et(s). The mutation is apparently specific for reversal of ethionine inhibition. The principal difference between the sensitive et(s) strain and the mutant was the latter's inability to concentrate large intracellular quantities of adenosylethionine. Reduced incorporation of ethyl groups or ethionine in other cellular fractions of the mutant was also detected. The data show that the mutant has not lost the ability to form adenosylethionine. It is suggested that the mutant has an increased ability to hydrolyze this sulfonium compound after it has been synthesized. It is possible that some of the ethionine is detoxified before it can participate in protein or adenosylethionine synthesis. No mutant alteration in accumulation of ethionine from the medium was detected. In the presence of ethionine, the parental strain accumulated 25 times more adenosylethionine than did the mutant. However, with methionine, only twice as much adenosylmethionine was accumulated by the parental strain as by the mutant.