Cloning of a new allelic variant of a Saccharomyces diastaticus glucoamylase gene and its introduction into industrial yeasts.

A new allelic variant of the STA2 gene, designated as STA2K, coding for a secreted glucoamylase, was cloned. Differences were revealed both in the structural gene and in the promoter region, as compared to other STA genes. The most peculiar structural features of STA2K are 1. a 1.1-kb natural deletion in its promoter located 189 nucleotides upstream of the translation start codon; and 2. an Asn-->Asp single amino acid change within the putative active site of the encoded glucoamylase. Neither the presence of glucose in the medium nor the host cell's mating type constellation affected the expression level of STA2K in S. cerevisiae. Self-replicating yeast plasmids containing STA2K were constructed and used to transform a laboratory yeast strain and various brewing strains. Pilot brewing tests with glucoamylase-secreting transformants of a brewing strain produced superattenuated beers at accelerated fermentation rates.