title: Streptomyces coelicolor XdhR is a direct target of (p)ppGpp that controls expression of genes encoding xanthine dehydrogenase to promote purine salvage.
abstract: The gene encoding Streptomyces coelicolor xanthine dehydrogenase regulator (XdhR) is divergently oriented from xdhABC, which encodes xanthine dehydrogenase (Xdh). Xdh is required for purine salvage pathways. XdhR was previously shown to repress xdhABC expression. We show that XdhR binds the xdhABC-xdhR intergenic region with high affinity (Kd ∼ 0.5 nM). DNaseI footprinting reveals that this complex formation corresponds to XdhR binding the xdhR gene promoter at two adjacent sites; at higher protein concentrations, protection expands to a region that overlaps the transcriptional and translational start sites of xdhABC. While substrates for Xdh have little effect on DNA binding, GTP and ppGpp dissociate the DNA-XdhR complex. Progression of cells to stationary phase, a condition associated with increased (p)ppGpp production, leads to elevated xdhB expression; in contrast, inhibition of Xdh by allopurinol results in xdhB repression. We propose that XdhR is a direct target of (p)ppGpp, and that expression of xdhABC is upregulated during the stringent response to promote purine salvage pathways, maintain GTP homeostasis and ensure continued (p)ppGpp synthesis. During exponential phase growth, basal levels of xdhABC expression may be achieved by GTP serving as a lower-affinity XdhR ligand.
authors.affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA.
authors.forename: Smitha
authors.initials: S
authors.lastname: Sivapragasam
authors.affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA.
authors.forename: Anne
authors.initials: A
authors.lastname: Grove
mesh_terms: D000493:Allopurinol / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006158:Guanosine Pentaphosphate / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006706:Homeostasis; D011401:Promoter Regions, Genetic; D011687:Purines / Q000378:metabolism*; D048372:Streptomyces coelicolor / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D019820:Xanthine / Q000378:metabolism; D014968:Xanthine Dehydrogenase / Q000235:genetics* / Q000378:metabolism
chemical_list: D011687:Purines; D014157:Transcription Factors; D019820:Xanthine; D006158:Guanosine Pentaphosphate; D000493:Allopurinol; D006160:Guanosine Triphosphate; D014968:Xanthine Dehydrogenase