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The Small Molecule ppGpp Induces Expression of the xdhABC G ene Cluster in Streptomyces coelicolor
Author(s) -
Sivapragasam Smitha,
Grove Anne
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.880.15
Subject(s) - streptomyces coelicolor , biochemistry , operon , gene cluster , gene , xanthine , purine , serine , microbiology and biotechnology , biology , purine metabolism , chemistry , gene expression , xanthine dehydrogenase , enzyme , escherichia coli , mutant , xanthine oxidase
Streptomyces coelicolor encodes Xanthine dehydrogenase regulator (XdhR) protein, whose gene is divergently oriented to the xanthine dehydrogenase ABC ( xdhABC ) gene cluster. The xdhABC operon encodes xanthine dehydrogenase, which functions in purine degradation and purine salvage pathways. Electrophoretic mobility shift assays reveal that XdhR binds to the intergenic region between these divergently oriented genes with Kd of 2.7±1nM. Of several ligands tested for attenuation of DNA binding by XdhR, ppGpp most effectively dissociated the DNA‐protein complex, with IC 50 of 2.06±0.61mM. In Streptomyces coelicolor , addition of serine hydroxamate (which mimics amino acid starvation) or progression of the cells to stationary phase is associated with increased levels of (p)ppGpp. Our RT‐PCR results show that expression of the xdhB gene is increased approximately four‐fold upon exposure of S. coelicolor to serine hydroxamate, and it is six‐fold higher in stationary phase when compared to the treatment with serine hydroxamate. We propose that (p)ppGpp induces expression of the xdhABC gene cluster by binding XdhR and relieving its repression. We suggest that xdhABC expression is enhanced to promote purine salvage pathways and sustain further (p)ppGpp synthesis under conditions of limiting nutrients.This is the first demonstration of the “alarmone ppGpp” acting directly with a transcription factor promoting gene expression.