Investigating ester metabolism: Characterization of the ATF1gene in Saccharomyces cerevisiae

Esters, which are produced during fermentation, are important contributors to the flavor of beer and whisky. Many different esters are formed during wort fermentations, however, most research has centered on the production of acetate esters. The mechanisms that regulate ester metabolism are not well characterized but it has been known for many years that ester levels produced during fermentation are influenced by a variety of factors. Nevertheless, it is unclear how these environmental factors influence yeast metabolism and, accordingly, ester synthesis. The enzyme alcohol acetyltransferase has been implicated in the formation of acetate esters and, as a result, most work has concentrated on the role of this enzyme. However, alcohol acetyltransferase is an extremely unstable protein when it has been purified; consequently, it is difficult to study. In this work, we have developed an in vivo system to study the expression of the gene encoding alcohol acetyltransferase, ATF1. A 3.3 kb BamHI/ XbaI fragment of ATF1, containing 1.9 kb of native promoter sequence, was fused to the Escherichia coli lacZ gene, and expression of ATF1 was measured under different conditions. Expression of ATF1 correlated with the production of ethyl acetate during fermentation. There was no clear relationship between ATF1 expression and isoamyl acetate production. © 1997 American Society of Brewing Chemists, Inc.