Stoichiometry of binding of CysB to the cysJIH, cysK, and cysP promoter regions of Salmonella typhimurium

J Bacteriol. 1994 Jun;176(12):3673-82. doi: 10.1128/jb.176.12.3673-3682.1994.


CysB is a member of the LysR family of transcriptional activators and regulates genes of the cysteine regulon in Salmonella typhimurium and Escherichia coli. CysB binds to specific sites just upstream of the -35 regions of the cysJIH, cysK, and cysP promoters, where, in the presence of N-acetyl-L-serine, it stimulates transcription initiation. The cysK and cysP promoters contain additional binding sites, and we have proposed that CysB bends these promoters by binding to adjacent sites. N-Acetyl-L-serine is thought to decrease the magnitude of such bending. Since stoichiometric data bearing on this model have been lacking, we analyzed complexes in gel mobility shift experiments with 35S-labeled CysB and 32P-labeled promoter fragments. CysB was found to bind as a tetramer, and N-acetyl-L-serine increased the electrophoretic mobilities of one-protein complexes of the multibinding site cysK and cysP promoters without changing their stoichiometry, indicating that a single CysB tetramer can bend these promoters and that N-acetyl-L-serine diminishes such bending. Bend angles for both promoters were calculated to be 100 and 50 degrees in the absence and presence of N-acetyl-L-serine. N-Acetyl-L-serine affected neither the stoichiometry nor the electrophoretic mobility of cysJIH promoter complexes, which are not known to contain bent DNA. DNA bending may be a mechanism for sequestering CysB at certain promoter sites by increasing their affinity for this protein in the absence of N-acetyl-L-serine.

Publication types

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

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Bacterial Proteins / pharmacology
  • Cysteine / biosynthesis
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / metabolism
  • DNA-Binding Proteins / metabolism*
  • Genes, Bacterial / genetics*
  • Models, Genetic
  • Nucleic Acid Conformation / drug effects
  • Promoter Regions, Genetic / genetics*
  • Protein Binding
  • Protein Conformation
  • Regulon / genetics
  • Salmonella typhimurium / genetics*
  • Salmonella typhimurium / metabolism
  • Serine / analogs & derivatives
  • Serine / pharmacology
  • Transcription Factors / genetics
  • Transcription, Genetic


  • Bacterial Proteins
  • CysB protein, Bacteria
  • CysB protein, Salmonella typhimurium
  • DNA, Bacterial
  • DNA-Binding Proteins
  • Transcription Factors
  • Serine
  • LysR protein, Bacteria
  • Cysteine
  • N-acetylserine