Characteristics of Saccharomyces cerevisiae gal1Δ and gal1Δhxk2Δ mutants expressing recombinant proteins from the GAL promoter

Galactose can be used not only as an inducer of the GAL promoters, but also as a carbon source by Saccharomyces cerevisiae, which makes recombinant fermentation processes that use GAL promoters complicated and expensive. To overcome this problem during the cultivation of the recombinant strain expressing human serum albumin (HSA) from the GAL 10 promoter, a gal 1Delta mutant strain was constructed and its induction kinetics investigated. As expected, the gal1Delta strain did not use galactose, and showed high levels of HSA expression, even at extremely low galactose concentrations (0.05 -0.1 g/L). However, the gal1Delta strain produced much more ethanol, in a complex medium containing glucose, than the GAL1 strain. To improve the physiological properties of the gal1Delta mutant strain as a host for heterologous protein production, a null mutation of either MIG1 or HXK2 was introduced into the gal1Delta mutant strain, generating gal1Deltamig1Delta and gal1Deltahxk2Delta double strains. The gal1Deltahxk2A strain showed a decreased rate of ethanol synthesis, with an accelerated rate of ethanol consumption, compared to the gal1Delta strain, whereas the gal1Deltamig1Delta strain showed similar patterns to the gal1Delta strain. Furthermore, the gal1Deltahxk2Delta strain secreted much more recombinant proteins (HSA and HSA fusion proteins) than the other strains. The results suggest that the gal1Deltahxk2Delta strain would be useful for the large-scale production of heterologous proteins from the GAL 10 promoter in S. cerevisiae. (C) 2005 Wiley Periodicals, Inc.