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 STA2(K), coding for a secreted glucoamylase, was cloned. Differences were revealed bot h in the structural gene and in the promoter region, as compared to ot her STA genes. The most peculiar structural features of STA2(K) are 1. a 1.1-kb natural deletion in its promoter located 189 nucleotides ups tream of the translation start codon; and 2. an Asn --> Asp single ami no acid change within the putative active site of the encoded glucoamy lase. Neither the presence of glucose in the medium nor the host cell' s mating type constellation affected the expression level of STA2(K) i n S. cerevisiae. Self-replicating yeast plasmids containing STA2(K) we re constructed and used to transform a laboratory yeast strain and var ious brewing strains. Pilot brewing tests with glucoamylase-secreting transformants of a brewing strain produced superattenuated beers at ac celerated fermentation rates.