Expression of the STA2 glucoamylase gene of Saccharomyces cerevisiae in brewers' yeast

Two fragments of DNA containing the Saccharomyces cerevisiae STA2 glucoamylase gene, with differing lengths of 5' non-coding DNA, were separately subcloned into a yeast centromeric plasmid. Of these two subclones, only the shorter one (containing 127 base-pairs of 5' non-coding DNA) was able to confer glucoamylase production on a standard laboratory strain of S. cerevisiae. The longer subclone (containing 465 bp of 5' non-coding DNA) did, however, confer glucoamylase production on a strain of S. cerevisiae lacking a functional STA10 gene (which encodes a repressor of STA2 gene expression). All-yeast plasmids lacking bacterial DNA were constructed from the two STA2 subclones for the transformation of a lager brewing yeast. Only the shorter STA2 subclone conferred glucoamylase activity on this yeast. The level of enzyme activity was comparable to that produced by the same yeast strain containing STA2 expressed from the PGK1 (that is, PGK1) promoter.