INDUCED EXPRESSION OF BACTERIAL BETA-GLUCOSIDASE ACTIVITY IN SACCHAROMYCES

The bglA gene which encodes a beta-glucosidase from Bacillus polymyxa, has been expressed in Saccharomyces cerevisiae under control of the y east CYC-GAL promoter. Strains have been constructed which carry the g ene in different locations: in a multicopy plasmid, a single integrati on at the URA3 locus, or multiple integrations at the RDN1 locus. Inte grative transformation at RDN1 yielded genetically stable clones with a high level of beta-glucosidase activity. Coordinated overexpression of the GAL4 inducer protein further increased the level of enzyme acti vity, although eventually caused the lysis of the cultures. Diploid, t riploid and tetraploid strains derived from the transformants with mul tiple integrations were constructed and expression of beta-glucosidase activity in different conditions of growth was assayed. While per-cel l activity increased with ploidy, specific activity was about the same in strains of equivalent genotype regardless of ploidy. Genetically s table and regulated expression in Saccharomyces of beta-glucosidase ac tivity is interesting for the development of strains able to ferment b eta-glycosidic sugars (i.e. cellobiose and lactose). From another poin t of view, the bglA product proved to be a convenient reporter enzyme to monitor heterologous gene expression.