Abstract
The breeding of a recombinant yeast having glucoamylase activity, Saccharomyces cerevisiae SR93, has already been reported by the authors, and further improvement of this yeast is attempted to significantly increase the conversion rate of starch into ethanol. It is generally known that the disruption of the MAT locus, which produces a repressor protein, enhances the expression of glucoamylase gene. A glucoamylase-producing yeast with the disrupted MAT locus, Saccharomyces cerevisiae SR96, is bred to convert starch into ethanol rapidly. Disruption of the MAT locus is performed by inserting the LEU2 gene into the MAT locus of S. cerevisiae SR93 and was confirmed by Southern blot analysis. The induction effect of starch and the repression effect of glucose on the glucoamylase synthesis are examined experimentally. The glucoamylase activity per unit cell concentration increases about 1.6-fold due to the disruption of the MAT locus. The specific growth rate, the glucoamylase synthesis rate, and the ethanol production rate of S. cerevisiae SR96 are much higher than S. cerevisiae SR93, and the direct alcohol fermentation of starch using S. cerevisiae SR96 gave the highest ethanol production rate in the various incubation systems.
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