Alcohol acetyltransferase (AATase) catalyzes the synthesis of isoamyl acetate from isoamyl alcohol and acetyl coenzyme A. Isoamyl acetate is one of important flavor components of beer. The bottom fermenting yeast S. pastorianus has one ATF1 gene and a homologous gene called Lg-ATF1 which encode AATaseI, and an ATF2 gene which encodes AATaseII. Southern blot analysis indicated that the ATF1 gene was located on two chromosomes of different size (1000 kb and 1050 kb) in S. pastorianus, and located on chromosome XV in S. cerevisiae. The Lg-ATF1 gene and the S. bayanus Lg- ATF1 homologue were both located on the 850 kb chromosome. These data suggested that the S. pastorianus ATF1 and Lg-ATF1 genes were derived from the S. cerevisiae ATF1 gene and the S. bayanus ATF1 homologue, respectively. The ATF2 gene was found to be located on the 1050 kb chromosome in S. pastorianus and on choromosome VII in S. cerevisiae, but was not detected in S. bayanus . These data suggested that the S. pastorianus ATF2 gene was derived from the S. cerevisiae ATF2 gene. Analysis using the ATF-lacZ fusion genes in S. pastorianus indicated that expression of both the ATF1 and Lg-ATF1 genes was repressed by oxygen and UFA, while the expression of the ATF2 gene was repressed by oxygen, but was unaffected by UFA.