title: Cross-talk between cognate and noncognate RpoE sigma factors and Zn(2+)-binding anti-sigma factors regulates photooxidative stress response in Azospirillum brasilense.
abstract: OBJECTIVE
  Azospirillum brasilense harbors two redox-sensitive Zinc-binding anti-sigma (ZAS) factors (ChrR1 and ChrR2), which negatively regulate the activity of their cognate extra-cytoplasmic function (ECF) σ factors (RpoE1 and RpoE2) by occluding their binding to the core enzyme. Both pairs of RpoE-ChrR control responses to photooxidative stress. The aim of this study was to investigate whether the two RpoE-ChrR pairs cross-talk while responding to the stress.
  
  
  RESULTS
  In silico analysis showed a high sequence similarity between ChrR1 and ChrR2 proteins, but differences in redox sensitivity. Using in silico and in vitro methods of protein-protein interaction, we have shown that both ChrR1 and ChrR2 proteins physically bind to their noncognate RpoE proteins. Restoration of the phenotypes of chrR1::Tn5 and chrR2::Km mutants related to carotenoid biosynthesis and photooxidative stress tolerance by expressing chrR1 or chrR2 provided in vivo evidence for the cross-talk. In addition, up- or down-regulation of several identical proteins by expressing chrR1 or chrR2 in the chrR1::Tn5 mutant provided another in vivo evidence for the cross-talk.
  
  
  METHODS
  Although multiple redox-sensitive ZAS anti-σ factors occur in some Gram-positive bacteria, no cross-talk is reported among them. We report here, for the first time, that the two ZAS anti-σ factors of A. brasilense also interact with their noncognate σ factors and affect gene expression.
  
  
  CONCLUSIONS
  The two redox-sensitive ZAS anti-σ factors in A. brasilense may interact with their cognate as well as noncognate ECF σ factors to play an important role in redox homeostasis by facilitating recovery from the oxidative stress.
authors.affiliation: Faculty of Science, School of Biotechnology, Banaras Hindu University , Varanasi, India .
authors.forename: Namrata
authors.initials: N
authors.lastname: Gupta
authors.forename: Ankush
authors.initials: A
authors.lastname: Gupta
authors.forename: Santosh
authors.initials: S
authors.lastname: Kumar
authors.forename: Rajeev
authors.initials: R
authors.lastname: Mishra
authors.forename: Chhaya
authors.initials: C
authors.lastname: Singh
authors.forename: Anil Kumar
authors.initials: AK
authors.lastname: Tripathi
mesh_terms: D015806:Azospirillum brasilense / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002338:Carotenoids / Q000096:biosynthesis; D004579:Electron Transport; D015964:Gene Expression Regulation, Bacterial; D008958:Models, Molecular; D009154:Mutation; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010641:Phenotype; D011485:Protein Binding; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D020543:Proteome; D040901:Proteomics; D012808:Sigma Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D015032:Zinc / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D020543:Proteome; D012808:Sigma Factor; D014157:Transcription Factors; D002338:Carotenoids; D015032:Zinc