Efficient utilization of starch by a recombinant strain of Saccharomyces cerevisiae producing glucoamylase and isoamylase.

Two plasmids, designated pRTI and pTI, were constructed to allow the integration of a bacterial isoamylase gene (iso) into Saccharomyces cerevisiae G23-8 chromosome. The integrative plasmid pRTI comprises the iso gene from Pseudomonas amyloderamosa, a portion of S. cerevisiae ribosomal DNA (rDNA), S. cerevisiae trp1 gene deficient in promoter and the bacterial vector pSP72. The structure of plasmid pTI is similar to that of pRTI, except that it lacks an rDNA segment. The Aspergillus awamori glucoamylase and P. amyloderamosa isoamylase genes were expressed in the recombinant strain of S. cerevisiae under the control of the yeast alcohol dehydrogenase gene (adh1) promoter. Southern-blot analysis showed that these plasmids were integrated into the yeast chromosome in tandem repeat and dispersion copies. The recombinant strains could assimilate starch more efficiently than the recipient strain with a conversion rate of greater than 95%.