Effect of DNA gyrase inhibitors and urea on the expression of cysB, the regulatory gene of the cysteine regulon

J Gen Microbiol. 1986 Sep;132(9):2571-6. doi: 10.1099/00221287-132-9-2571.


cysB, the regulatory gene of the cysteine regulon, is autoregulated. Inhibitors of both gyrase subunits, nalidixic acid and novobiocin, affect the expression of cysB, as monitored by beta-galactosidase activity in cysB::lac fusion strains. In gyrA mutants that are resistant to nalidixic acid, this drug does not affect cysB expression. The amount of mRNA transcribed from the cysB promoter isolated from cultures grown in the presence of gyrase inhibitors was significantly lower than that from the control culture without inhibitors. Urea also decreased cysB expression. These results suggest that DNA topology could play a role in cysB expression.

MeSH terms

  • Cysteine / genetics*
  • Escherichia coli / genetics
  • Gene Expression Regulation / drug effects*
  • Genes, Regulator / drug effects*
  • Lac Operon / drug effects
  • Nalidixic Acid / pharmacology
  • Novobiocin / pharmacology
  • Nucleic Acid Hybridization
  • RNA, Bacterial
  • Topoisomerase II Inhibitors*
  • Transcription, Genetic / drug effects
  • Urea / pharmacology*
  • beta-Galactosidase / metabolism


  • RNA, Bacterial
  • Topoisomerase II Inhibitors
  • Novobiocin
  • Nalidixic Acid
  • Urea
  • beta-Galactosidase
  • Cysteine