Structural and functional requirements for the chromatin transition at the PHO5 promoter in Saccharomyces cerevisiae upon PHO5 activation.

The PHO5 promoter from Saccharomyces cerevisiae can exist in two chromatin configurations depending on its state of activity. In the repressed promoter a short hypersensitive site containing a binding site for the transcription factor PHO4 is flanked by specifically positioned nucleosomes. After induction two nucleosomes upstream and two downstream of the hypersensitive site are disrupted, and the entire promoter becomes accessible.

Nucleosome disruption at the yeast PHO5 promoter upon PHO5 induction occurs in the absence of DNA replication.

Activation of the PHO5 gene in S. cerevisiae by phosphate starvation was previously shown to be accompanied by the disappearance of four positioned nucleosomes from the promoter. To investigate the mechanism, we replaced the PHO80 gene, a negative regulator of PHO5, by a temperature-sensitive allele.

Activation of the weakly regulated PHO8 promoter in S. cerevisiae: chromatin transition and binding sites for the positive regulatory protein PHO4.

PHO8 encodes an alkaline phosphatase in Saccharomyces cerevisiae whose transcription is regulated by the phosphate concentration in the medium. This occurs through the action of several positive and negative regulatory proteins, also involved in the regulation of other members of the phosphatase gene family. A central role is played by PHO4, the gene encoding a DNA binding regulatory protein.

Role of trans-activating proteins in the generation of active chromatin at the PHO5 promoter in S. cerevisiae.

Induction of the PHO5 gene in Saccharomyces cerevisiae by phosphate starvation was previously shown to be accompanied by the removal of four positioned nucleosomes from the promoter. We have now investigated the role of two trans-activating proteins, encoded by PHO2 and PHO4, which bind to the PHO5 promoter. Both proteins are absolutely required for the chromatin transition to occur as shown by analysis of null mutants of the two genes.