Transcription-defective soxR mutants of Escherichia coli: isolation and in vivo characterization

J Bacteriol. 2003 Apr;185(8):2441-50. doi: 10.1128/JB.185.8.2441-2450.2003.


The soxRS regulon protects Escherichia coli from superoxide and nitric oxide stress. SoxR protein, a transcription factor that senses oxidative stress via its [2Fe-2S] centers, transduces the signal to the soxS promoter to stimulate RNA polymerase. Here we describe 29 mutant alleles of soxR that cause defects in the activation of soxS transcription in response to paraquat, a superoxide stress agent. Owing to the selection and screen used in their isolation, most of these mutant alleles encode proteins that retained specific binding activity for the soxS promoter in vivo. The mutations were found throughout the SoxR polypeptide, although those closer to the N terminus typically exhibited greater defects in DNA binding. The degree of the defect in the transcriptional response to superoxide caused by each mutation was closely paralleled by its impaired response to nitric oxide. This work begins the general identification of the residues in the SoxR polypeptide that are critical for transducing oxidative stress signals into gene activation.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alleles
  • Amino Acid Sequence
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / isolation & purification
  • Bacterial Proteins / metabolism
  • Escherichia coli / chemistry
  • Escherichia coli / genetics*
  • Escherichia coli Proteins / genetics
  • Gene Expression
  • Gene Expression Regulation
  • Molecular Sequence Data
  • Mutation
  • Nitric Oxide / pharmacology
  • Oxidative Stress
  • Paraquat / pharmacology
  • Promoter Regions, Genetic
  • Protein Binding
  • Sequence Alignment
  • Trans-Activators / genetics
  • Transcription Factors / genetics*
  • Transcription Factors / isolation & purification
  • Transcription Factors / metabolism
  • Transcription, Genetic*
  • Transcriptional Activation


  • Bacterial Proteins
  • Escherichia coli Proteins
  • Trans-Activators
  • Transcription Factors
  • SoxR protein, Bacteria
  • SoxS protein, E coli
  • Nitric Oxide
  • Paraquat