Regulation of endo-polygalacturonase activity in Saccharomyces cerevisiae

Pectolytic activity in Saccharomyces cerevisiae is due to the secretion of an endo-polygalacturonase encoded by the PGU1 gene. The ability to degrade polygalacturonic acid has been shown to vary between different strains. In this study, we attempted to elucidate how pectolytic activity is regulated in S. cerevisiae and to determine whether the means of regulation differ between strains. Saccharomyces cerevisiae strains from different genetic backgrounds, with varying ability to degrade pectin, were compared. Activity was found not to be regulated by sequence differences in the PGU1 gene, but by the transcription level of the gene. Expression of PGU1 was found to be determined by the transcription level of its two transcription factors TEC1 and STE12. The activation of PGU1 transcription by galactose was found to be strain specific, independent of the strain being an industrial or a domesticated one. The EUROSCARF yeast deletion library was screened for genes encoding inhibitors and activators of polygalacturonase activity. Fourteen strains were identified, in which deletion of a specific gene resulted in a recovery of polygalacturonase activity; these genes were identified as encoding inhibitors of polygalacturonase activity, and two activators were identified.