Genetic evidence that high noninduced maltase and maltose permease activities, governed by MALx3-encoded transcriptional regulators, determine efficiency of gas production by baker's yeast in unsugared dough

Strain selection and improvement in the baker's yeast industry have aimed t o increase the speed of maltose fermentation in order to increase the leave ning activity of industrial baking yeast. We identified two groups of baker 's strains of Saccharomyces cerevisiae that can be distinguished by the mod e of regulation of maltose utilization. One group (nonlagging strains), cha racterized by rapid maltose fermentation, had at least 12-fold more maltase and 130-fold-higher maltose permease activities than maltose-lagging strai ns in the absence of inducing sugar (maltose) and repressing sugar (glucose ). Increasing the noninduced maltase activity of a lagging strain 13-fold l ed to an increase in CO2 production in unsugared dough. This increase in CO 2 production also was seen when the maltose permease activity was increased 55-fold. Only when maltase and maltose permease activities were increased in concert was CO2 production by a lagging strain similar to that of a nonl agging strain. The noninduced activities of maltase and maltose permease co nstitute the largest determinant of whether a strain displays a nonlagging or a lagging phenotype and are dependent upon the MALx3 allele. Previous st rategies for strain improvement have targeted glucose derepression of malta se and maltose permease expression. Our results suggest that increasing non induced maltase and maltose permease levels is an important target for impr oved maltose metabolism in unsugared dough.