The Amplification Effect of the ILV5 Gene on the Production of Vicinal Diketones in Saccharomyces Cerevisiae¹

1 Presented at the 52nd Annual Meeting, Tucson, AZ, May 1986.

Abstract

In brewery fermentation, improved control of diacetyl and 2,3-pentanedione formed by spontaneous oxidative decarboxylation might be achieved by increasing the anabolic flow of intermediates leading to isoleucine and valine. Following this approach, the effect of amplification of the reductoisomerase (ILV5) gene on production of vicinal diketones under derepressing and repressing growth conditions was studied. The wild type ILV5 gene was selected by transformation of a haploid ilv5 ura3 mutant strain of Saccharomyces cerevisiae. In similar experiments, the gene ILV5 was cloned into a prototrophic strain for this character. The net result was a five- to 10-fold increase in the reductoisomerase activity and a concomitant decrease of about 50–60% of maximum vicinal diketone levels compared to the control yeast. Moreover, a similar reciprocal relationship was observed under repressing and derepressing conditions. The reduced ability to produce vicinal diketones as a result of amplification is a good indication that reductoisomerase is one of the rate-limiting steps for the conversion of acetohydroxy acids to isoleucine and valine.

• Amino acid
• Biosynthesis
• Genetics
• Reductoisomerase
• Repression
• Vicinal diketones