A nucleosome precludes binding of the transcription factor Pho4 in vivo to a critical target site in the PHO5 promoter.
AUTOR(ES)
Venter, U
RESUMO
Activation of the Saccharomyces cerevisiae PHO5 gene by phosphate starvation is accompanied by the disappearance of two pairs of positioned nucleosomes that flank a short hypersensitive region in the promoter. The transcription factor Pho4 is the key regulator of this transition. By in vitro footprinting it was previously shown that there is a low affinity site (UASp1) which is contained in the short hypersensitive region in the inactive promoter, and a high affinity site (UASp2) which is located in the adjacent nucleosome. To investigate the interplay between nucleosomes and Pho4, we have performed in vivo footprinting experiments with dimethylsulfate. Pho4 was found to bind to both sites in the active promoter. In contrast, it binds to neither site in the repressed promoter. Lack of binding under repressing conditions is largely due to the low affinity of Pho4 for its binding sites under these conditions. Despite the increased affinity of Pho4 for its target sites under activating conditions, binding to UASp2 is prevented by the presence of the nucleosome and can only occur after prior disruption of this nucleosome in a process that requires UASp1. Protection of the PHO5 UASp2 by the nucleosome is not absolute, however, since overexpression of Pho4 can disrupt this nucleosome even when UASp1 is deleted. Also under these conditions, with only UASp2 present, all four nucleosomes at the PHO5 promoter are disrupted, whereas no chromatin change at all is observed when both UAS elements are destroyed.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=395424Documentos Relacionados
- The transactivation domain of Pho4 is required for nucleosome disruption at the PHO5 promoter.
- Cooperative Pho2-Pho4 Interactions at the PHO5 Promoter Are Critical for Binding of Pho4 to UASp1 and for Efficient Transactivation by Pho4 at UASp2
- The homeodomain protein Pho2 and the basic-helix-loop-helix protein Pho4 bind DNA cooperatively at the yeast PHO5 promoter.
- The two positively acting regulatory proteins PHO2 and PHO4 physically interact with PHO5 upstream activation regions.
- Saccharomyces cerevisiae PHO5 promoter region: location and function of the upstream activation site.