Promoter analysis of the class 2 flagellar operons of Salmonella

Genes Genet Syst. 1999 Aug;74(4):179-83. doi: 10.1266/ggs.74.179.


The Salmonella flagellar operons are divided into three classes with reference to their relative positions in the transcriptional hierarchy. Expression of the class 2 operons requires the class 1 gene products, FlhD and FlhC, and is enhanced by an unknown mechanism in the presence of the class 3-specific sigma factor, FliA, and in the absence of its cognate anti-sigma factor, FlgM. In this study, the transcriptional start site mapping was performed by primer extension analysis for five class 2 operons, flgA, flgB, flhB, fliE and fliL. In all cases, one or a few major transcriptional start sites were identified. These start signals disappeared in the flhDC-mutant background, and their intensity decreased and increased in the fliA-mutant and flgM-mutant backgrounds, respectively. Therefore, we conclude that the FlhD/FlhC-dependent transcription is responsible for the FliA-dependent enhancement. Sequence comparison revealed that an imperfect inverted repetitious sequence is conserved upstream of the class 2 operons. Truncation of this sequence from the flgB promoter reduced its transcriptional activity to the background level, indicating that this is an essential cis-acting element for transcription of the class 2 operons.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Base Sequence
  • DNA, Bacterial
  • Escherichia coli Proteins*
  • Flagella / genetics*
  • Membrane Proteins*
  • Molecular Sequence Data
  • Operon*
  • Promoter Regions, Genetic*
  • Salmonella / genetics*


  • Bacterial Proteins
  • DNA, Bacterial
  • Escherichia coli Proteins
  • FlgA protein, Salmonella
  • FlhB protein, Bacteria
  • FliL protein, E coli
  • Membrane Proteins
  • fliE protein, E coli
  • FliL protein, Bacteria