Quantitative analysis of the impact of HXK2 and REG1 deletion in Saccharomyces cerevisiae on invertase expression and respiration

Abstract

In Saccharomyces cerevisiae, the genes HXK2 and REG1 are believed to play a central role in carbon catabolite repression, acting on multiple pathways in the central metabolism. The present study aimed at quantifying the effect of deletion of genes HXK2 or REG1, respectively, in the S. cerevisiae strain CEN.PK113-7D on the regulation of invertase and respiratory functions. Batch cultivation of the HXK2 deletion mutant on substrate mixtures of sucrose, fructose and glucose and on pure glucose showed an initial high invertase expression followed by a gradual decrease of specific invertase production as well as respiratory capacity. Our data strongly indicate that this regulatory pattern might be caused by a repression function exerted by the Hxk1 protein. This was concluded from the observation that the HXK2 deletion mutant on pure fructose, for which Hxk1 was the only remaining phosphorylating enzyme, was subjected to a considerably stronger invertase repression than on a fructose/sucrose mixture. The present study confirmed that deletion of HXK2 or REG1 alleviated carbon catabolite repression at any of the tested monosaccharide concentrations. The experiments showed that the deletions affected invertase expression and respiratory functions equally. This suggests that REG1 and HXK2 play a central role in the regulation of carbon catabolic pathways. Finally, we show that the deletion of HXK2 or REG1 enhanced respiratory functions but reduced the specific substrate uptake rate and, as a consequence, biomass productivity. An inverse correlation between oxidative capacity and specific substrate uptake rate was found to hold for all strains and all initial sugar mixtures examined in this work.