Creation of a synthetic xylose-inducible promoter for Saccharomyces cerevisiae

Saccharomyces cerevisiae is currently used to produce ethanol from glucose, but it cannot utilize five-carbon sugars contained in the hemicellulose component of biomass feedstocks.  S. cerevisiae strains engineered for xylose fermentation have been made using constitutive promoters to express the required genes.  However, these proteins are not required until glucose is consumed and xylose is available in the cell.  Constitutive expression of all of these genes can result in wasted cellular resources to produce proteins for enhanced xylose fermentation when xylose is not available.  In some cases, expression of these genes during glucose fermentation is detrimental to productivity.  Native xylose-assimilating yeasts regulate the expression of genes required for xylose uptake and metabolism in response to the availability of xylose.  This level of genetic control is lacking in yeasts like S. cerevisiae that have been engineered to ferment xylose.  Thus, a novel genetic circuit in S. cerevisiae is required to properly control the expression of genes specific to xylose metabolism.  We have developed new synthetic promoters for use in S. cerevisiae to control gene expression in response to the presence of xylose.  These new synthetic promoters will allow tunable control of gene expression for engineering Saccharomyces yeasts for efficient xylose fermentation.