engleski

Transcriptional Regulation in Yeast : Transcriptional Factors vs. Chromatin

Saccharomyces cerevisiae contains set of genes coding for proteins involved in phosphate uptake and metabolism, the expression of which is coordinatively regulated in response to inorganic phosphate concentration in the medium. The most strongly regulated gene is PHO5, which codes for acid phosphatase. In addition there is alkaline phosphatase, encoded by PHO8 gene, which transcription also increased as a consequence of phosphate starvation. The expression of the two genes is negatively regulated by the products of the PHO80 and PHO85 genes, while the products of PHO2, PHO4 and PHO81 act as positive regulators. Pho4 is itself negatively regulated through phosphorylation by the Pho80/Pho85 cyclin/CDK complex which in the turn is regulated by the phosphate level. Phosphorylated Pho4 is unable to interact with positive factor Pho2 and in addition it is exported into the cytoplasm. Despite the coordinatinate regulation of the two genes the PHO8 promoter is almost 10 times weaker then PHO5. Upon induction both promoters undergo characteristic chromatin remodelling, yet the extent of remodelling at the PHO8 promoter is significantly lower than at PHO5. Studies with the PHO8 promoter variants containing UAS elements from PHO5 showed close correlation between promoter activity and the extent of chromatin remodelling, strongly suggesting that the low level of PHO8 induction is partly due to the inability of Pho4 to achieve complete chromatin disruption at this promoter. Consistently, hystone acetylase (Gcn5) and SWI/SNF complex are required for chromatin remodelling at the PHO8 promoter, but not at PHO5.

S. cerevisiae;; transcriptional regulation; chromatin; PHO5; PHO8

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