engleski

The role of the SWI/SNF complex in chromatin remodeling at the PHO5 promoter in Saccharomyces cerevisiae

Phosphate (Pi) is an essential nutrient for all organisms, needed for the biosynthesis of diverse cellular components, including nucleic acids, proteins, lipids and sugars. Phosphate starvation induces the transcription of several structural and regulatory genes (the PHO regulon) involved in the acquisition of phosphate in the yeast Saccharomyces cerevisiae. Among the PHO genes, the PHO5 gene has become a well known system to investigate the role of chromatin structure in transcriptional regulation. The PHO5 gene, which encodes a secreted acid phosphatase, is repressed when yeast are grown under high phosphate conditions, and is induced upon phosphate depletion. Under repressing (+Pi) conditions, the PHO5 promoter is assembled into an array of four positioned nucleosomes interrupted by a short hypersensitive site located between nucleosomes-2 and -3. Activation of the gene is accompanied by the binding of the transactivator Pho4 to its cognate binding sites and the concomitant disruption of the four positioned nucleosomes, giving rise to a 600 bp hypersensitive region indicating the loss of all four nucleosomes or a profound alteration in their structure. This chromatin transition requires the transcription factor Pho4, the Pho4-binding sites in UASp1 and UASp2 as well as the activation domain of Pho4, but is independent of active transcription or replication. Still the precise mechanism underlying the alteration in PHO5 chromatin structure is not understood. As aforementioned the remodeling event is dependent on the activation domain of Pho4 and acidic activation domains have been shown to interact with components of the basal transcription machinery as well as with components of transcriptional coactivators including ATP-dependent chromatin-remodeling machines. Since chromatin remodeling is a prerequisite for transcriptional activation rather than the result of active transcription, it is assumed that Pho4 recruits remodeling activities to the PHO5 promoter region prior to the general transcription machinery. Data will be presented on the role of SWI/SNF in the activation of the PHO5 gene. In addition, the physical association of SWI/SNF with the promoter region before and after PHO5 induction has been investigated by the ChIP (Chromatin Immunoprecipitation) technology.

transcriptional regulation; chromatin remodeling; yeast PHO5 promoter

nije evidentirano