Abstract:  An integrative plasmid pMGI carrying yeast α-acetolactate synthase gene(ILV2),that used the cloned amylase gene(AMY)as the selective marker,was constructed from pBluescript M13-.The ilv2∷AM expression cassette released from pMGI was transformed into an industrial strain of Saccharomyces cerevisiae and integrated at the ILV2 gene of the host genome through one-step replacement,gaining transformants(Sc11-ilv)free of undesired sequences(bacterial or viral vector sequences and yeast selective marker).The α-acetolactate synthase activity of the recombinant strain was lowered by 30%.Fermentation tests confirmed that the diacetyl concentration was reduced by 70% in fermented wort by the recombinant strain,while the brewing performances of the recombinant strain were retained.This type of integration is genetically stable even after 100 generations of cell multiplication under non-selective conditions and can be used in beer production safely.

Key words: an industrial strain of S.cerevisiae, acetolactate synthase gene(ILV2), gene disruption, diacetyl, fermentation