The ATFi gene, which encodes alcohol acetyltransferase (AATase), was cloned from Saccharomyces cerevisiae and brewery lager yeast (Saccharomyces uvarum). The nucleotide sequence of the ATFI gene isolated from S. cerevisiae was determined. The structural gene consists of a 1,575-bp open reading frame that encodes 525 amino acids with a calculated molecular weight of 61,059. Although the yeast AATase is considered a membrane-bound enzyme, the results of a hydrophobicity analysis suggested that this gene product does not have a membrane-spanning region that is significantly hydrophobic. A Southern analysis of the yeast genomes in which the ATF] gene was used as a probe revealed that S. cerevisiae has one ATF) gene, while brewery lager yeast has one ATF1 gene and another, homologous gene (Lg-ATFI). Transformants carrying multiple copies of the ATF) gene or the Lg-ATFJ gene exhibited high AATase activity in static cultures and produced greater concentrations of acetate esters than the control.

Alcohol acetyltransferase (AATase) catalyzes the esterification of isoamyl alcohol by acetyl coenzyme A. The enzyme was solubilized from the microsomal fraction of Saccharomyces cerevisiae Kyokai No. 7, using Triton X-100 and then purified by a series of chromatographic separations: Poly Buffer Exchanger 94 (PBE94), DEAE Toyopearl, Toyopearl HW60, hydroxyapatite, Octyl-Sepharose CL-4B, and hexanol-affinity column chromatography. When the solubilized enzyme was put on PBE94, two active fractions were obtained. The enzyme obtained after affinity column chromatography had a single band on an SDS polyacrylamide gel, and its molecular mass was estimated to be 60 kDa. The enzyme was most active at pH 8.0 and 25 degrees C. It was stable between pH 7.5 and 8.5, but was unstable at temperatures above 10 degrees C. The activity was markedly inhibited by heavy metal ions such as Cd2+, Cu2+, Zn2+, and Hg2+, and sulfhydryl reagents. The Km for acetyl-CoA was 0.19 mM. The internal peptide sequences were also identified.

No abstract

The nucleotide sequences of alcohol acetyltransferase genes isolated from lager brewing yeast, Saccharomyces carlsbergensis have been determined. S. carlsbergensis has one ATF1 gene and another homologous gene, the Lg‐ATF1 gene. There was a high degree of homology between the amino acid sequences deduced for the ATF1 protein and the Lg‐ATF1 protein (75·7%), but the N‐terminal region has a relatively low degree of homology. Southern analysis and contour‐clamped homogeneous electric field analysis of Saccharomyces strains suggest that the ATF1 gene is located on chromosome XV in S. cerevisiae and that the Lg‐ATF1 gene might originate from the ‘non‐S. cerevisiae’ genome of S. carlsbergensis, which is similar to that of S. bayanus and S. pastorianus. The nucleotide sequence data reported in this paper will appear in the DDBJ, EMBL and GenBank data banks with the Accession Numbers D63449 (ATF1) and D63450 (Lg‐ATF1).

A new rapid transformation system for Aspergillus niger that uses electroporation to render intact germinating conidia permeable to DNA is described. The transformant colonies appeared earlier than transformants obtained by the protoplast-forming method. Without pretreatment of the conidia the transformation frequencies were 1.2 colonies per micrograms of integrative vector and 100 colonies per micrograms of plasmid DNA. When the conidia were treated with a dilute solution of fungal cell wall lytic enzyme, the frequency of transformation was increased by approx. 2-fold when using two vectors. Southern blot analysis of genomic DNA and restriction endonuclease-digested DNA from a random sample of transformants showed homologous and nonhomologous integration of the integrative vector into the genome, as is also observed with the protoplast-forming method. In transformation with the plasmid vector, the transformant DNA was shown to be mostly maintained in free form with minimal integration into the chromosome when transformed by either intact electroporation or the conventional method.