An efficient yeast gene expression system with GAL10 promoter that does not require galactose as an inducer was developed using Delta gal80 mutant strain of Saccharomyces cerevisiae. We constructed several combinations of gat mutations (Delta gal1, Delta gal80, Delta mig1, Delta mig2, and Delta gal6) of S. cerevisiae and tested for their effect on efficiency of recombinant protein production by GAL10 promoter using a lipase, Candida antarctica lipase B (CalB), as a reporter. While the use of Delta gal1 mutant strain required the addition of a certain amount of galactose to the medium, Delta gal80 mutant strain did not require galactose. Furthermore, it was found that the recombinant CAB could be produced more efficiently (1.6-fold at 5 L-scale fermentation) in Delta gal80 mutant strain than in the Delta gal1 mutant. The Delta gal80 mutant strain showed glucose repressible mode of expression of GAL10 promoter. Using Delta gal80 mutant strain of S. cerevisiae, CalB was efficiently produced in a glucose-only fermentation at volumes up to 500 L. (C) 2009 Elsevier Ltd. All rights reserved.