GENES THAT CAUSE OVERPRODUCTION OF ISOAMYL ALCOHOL BY INCREASED GENE-DOSAGE EFFECT IN SACCHAROMYCES-CEREVISIAE

Isoamyl acetate, one of the major components of flavor in a Japanese brewing product, sake, contributes to the fruity flavor of sake. We cloned Saccharomyces cerevisiae genes that cause overproduction of isoamyl alcohol, the precursor of isoamyl acetate, by increased gene-dosage effect. Three plasmids, pScFlr1, pScFlr2, and pScFlr3, were obtained by selection from the yeast genomic DNA which, on a multicopy plasmid, confer a phenotype resistant to 5,5,5-trifluoro-DL-leucine, an analogue of leucine. The cloned DNA fragments in the three plasmids had different restriction maps. Transformed cells with each of the plasmids produced large amounts of both isoamyl alcohol and isoamyl acetate. The gene cloned in the plasmid pScFlr1 was identified as the LEU4 gene encoding alpha-isopropylmalate synthase.