No abstract

No abstract

The PGU1 gene of Saccharomyces cerevisiae has been shown to encode a polygalacturonase. The polygalacturonase activity in S. cerevisiae is strain specific. There are no significant differences in the PGU1 promoter regions of strains with and without polygalacturonase activity. The PGU1 gene is subtelomeric because it is located within 25 kb of the right telomere of chromosome X. Expressions of genes located in subtelomeric regions in the yeast S. cerevisiae are inhibited compared with the rest of the genome. In this study, we showed that the deletion of genes involved in telomere silencing enhances polygalacturonase activity. PGU1 transcription and polygalacturonase activity are increased when PGU1 is shifted to a different location in the genome, away from the telomere located close to this gene, and the depletion of the histone H4 leads to an increase in PGU1 transcription. We concluded that PGU1 is silenced in strains without polygalacturonase activity due to an epigenetic effect. The results of this study suggest that PGU1 is silenced by being folded into a heterochromatin-like structure at its subtelomeric position on chromosome X. Formation of this silent structure is dependent on the Isw2p chromatin remodeling complex, its histone fold motif containing subunit Dls1p and the N-terminal tail of the H4 histone.

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.

No abstract

No abstract