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 Zn2Cys6 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 Zn2Cys6 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 pho1 and
tgp1 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 in silico analysis of available genome-wide ChIP-seq data, (iv) affirming that mutations in the two Pho7 recognition sites in the pho1 promoter efface pho1 expression in vivo, and (v) establishing that the
zinc-binding cysteines and a pair of conserved arginines in the DBD are essential for Pho7 activity in vivoIMPORTANCE 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 Zn2Cys6 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 in vivo 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.