Defining the DNA Binding Site Recognized by the Fission Yeast ZnCys Transcription Factor Pho7 and Its Role in Phosphate Homeostasis.

Fission yeast phosphate homeostasis entails transcriptional induction of genes encoding phosphate-mobilizing proteins under conditions of phosphate starvation. Transcription factor Pho7, a member of the ZnCys family of fungal transcription regulators, is the central player in the starvation response. The DNA binding sites in the promoters of phosphate-responsive genes have not been defined, nor have any structure-function relationships been established for the Pho7 protein. Here we narrow this knowledge gap by (i) delineating an autonomous DNA-binding domain (DBD) within Pho7 that includes the ZnCys module, (ii) deploying recombinant Pho7 DBD in DNase I footprinting and electrophoretic mobility shift assays (EMSAs) to map the Pho7 recognition sites in the promoters of the phosphate-regulated and genes to a 12-nucleotide sequence motif [5'-TCG(G/C)(A/T)xxTTxAA], (iii) independently identifying the same motif as a Pho7 recognition element via analysis of available genome-wide ChIP-seq data, (iv) affirming that mutations in the two Pho7 recognition sites in the promoter efface expression , and (v) establishing that the zinc-binding cysteines and a pair of conserved arginines in the DBD are essential for Pho7 activity Fungi respond to phosphate starvation by inducing the transcription of a set of phosphate acquisition genes that comprise a phosphate regulon. Pho7, a member of the ZnCys family of fungal transcription regulators, is the central player in the phosphate starvation response in fission yeast. The present study identifies a 12-nucleotide Pho7 DNA binding motif [5'-TCG(G/C)(A/T)xxTTxAA] in the promoters of phosphate-regulated genes, pinpoints DNA and protein features important for Pho7 binding to DNA, and correlates them with Pho7-dependent gene expression The results highlight distinctive properties of Pho7 vis-a-vis other fungal zinc binuclear cluster transcription factors as well as the divergent cast of transcription factors deployed for phosphate homeostasis in fission yeast versus budding yeast.