Redirection of the respiro-fermentative flux distribution in Saccharomycescerevisiae by overexpression of the transcription factor Hap4p

Reduction of aerobic fermentation on sugars by altering the fermentative/ox idative balance is of significant interest for optimization of industrial p roduction of Saccharonmyces cerevisiae. Glucose control of oxidative metabo lism in baker's yeast is partly mediated through transcriptional regulation of the Hap4p subunit of the Hap2/3/4/5p transcriptional activator complex. To alleviate glucose repression of oxidative metabolism, we constructed a yeast strain with constitutively elevated levels of Hap4p. Genetic analysis of expression levels of glucose-repressed genes and analysis of respirator y capacity showed that Hap4p overexpression (partly) relieves glucose repre ssion of respiration. Analysis of the physiological properties of the Hap4p overproducer in batch cultures in fermenters (aerobic, glucose excess) has shown that the metabolism of this strain is more oxidative than in the wil d-type strain, resulting in a significant reduced ethanol production and im provement of growth rate and a 40% gain in biomass yield. Our results show that modification of one or more transcriptional regulators can be a powerf ul and a widely applicable tool for redirection of metabolic fluxes in micr oorganisms.