Cloning and characterization of a gene complementing the mutation of an ethanol-sensitive mutant of sake yeast.

Ethanol-sensitive mutants (esl to es10) were isolated from sake yeast, Saccharomyces cerevisiae SY-32. These mutants were unable to grow at 7% ethanol at which the wild type strain SY-32 does grow. The mutants had a variety of fermentation rates and viabilities in the presence of ethanol. The gene ERG6, complementing the ethanol-sensitive mutation of es5, was cloned from an SY-32 gene library. ERG6 encodes S-adenosylmethionine: delta 24-sterol-C-methyltransferase (EC 2.1.1.41) in the ergosterol synthetic pathway. Mutant es5 had a reduced ability to synthesize ergosterol. An erg6 disruptant was also ethanol-sensitive. These results suggested that ERG6 plays an important role in the ethanol tolerance of S. cerevisiae.