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Gene Review

fliG  -  flagellar motor switch protein FliG

Salmonella enterica subsp. enterica serovar Typhimurium str. LT2

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Disease relevance of fliG

  • Mutations in Salmonella typhimurium fliG, fliM and fliN give rise either to non-flagellate, non-motile or non-chemotactic mutant bacteria [1].
  • Specifically, the presence of a plasmid expressing treponemal fliG reduced swarming motility in S. typhimurium, while in Escherichia coli, this plasmid conferred a nonmotile phenotype and a reduction in flagellar number [2].

High impact information on fliG

  • This localization was made possible by the discovery of two spontaneous mutants in which the fliF (M ring) and fliG (switch) genes were fused in-frame [3].
  • During bacterial chemotaxis, the binding of stimulatory ligands to chemoreceptors at the cell periphery leads to a response at the flagellar motor [4].
  • MotA and MotB are cytoplasmic membrane proteins that form the force-generating unit of the flagellar motor in Salmonella typhimurium and many other bacteria [5].
  • This explains why single, missense fliN, fliG or fliM mutations, found in many non-motile strains, can alter the belled morphology [6].
  • The basal disk may anchor the flagellar motor to the cell wall in some polar bacteria, but this does not seem to be a unique strategy [7].

Biological context of fliG


Anatomical context of fliG

  • The bacterial flagellum is a motile organelle, and the flagellar hook is a short, highly curved tubular structure that connects the flagellar motor to the long filament acting as a helical propeller [9].

Other interactions of fliG

  • An extreme clockwise switch bias mutation in fliG of Salmonella typhimurium and its suppression by slow-motile mutations in motA and motB [10].
  • All of the second-site mutations in motA and motB caused some impairment of motility, both in the pseudorevertants and in a wild-type fliG background [10].
  • The mechanism of suppression of the fliG mutation by the mot mutations is complex, involving destabilization of the right-handed flagellar bundle as a result of reduced motor speed [10].


  1. Structural effects of mutations in Salmonella typhimurium flagellar switch complex. Zhao, R., Schuster, S.C., Khan, S. J. Mol. Biol. (1995) [Pubmed]
  2. Genetic and transcriptional analysis of flgB flagellar operon constituents in the oral spirochete Treponema denticola and their heterologous expression in enteric bacteria. Heinzerling, H.F., Olivares, M., Burne, R.A. Infect. Immun. (1997) [Pubmed]
  3. Localization of the Salmonella typhimurium flagellar switch protein FliG to the cytoplasmic M-ring face of the basal body. Francis, N.R., Irikura, V.M., Yamaguchi, S., DeRosier, D.J., Macnab, R.M. Proc. Natl. Acad. Sci. U.S.A. (1992) [Pubmed]
  4. CheA protein, a central regulator of bacterial chemotaxis, belongs to a family of proteins that control gene expression in response to changing environmental conditions. Stock, A., Chen, T., Welsh, D., Stock, J. Proc. Natl. Acad. Sci. U.S.A. (1988) [Pubmed]
  5. Deletion analysis of MotA and MotB, components of the force-generating unit in the flagellar motor of Salmonella. Muramoto, K., Macnab, R.M. Mol. Microbiol. (1998) [Pubmed]
  6. FliN is a major structural protein of the C-ring in the Salmonella typhimurium flagellar basal body. Zhao, R., Pathak, N., Jaffe, H., Reese, T.S., Khan, S. J. Mol. Biol. (1996) [Pubmed]
  7. Conserved machinery of the bacterial flagellar motor. Stahlberg, A., Schuster, S.C., Bauer, M., Baeuerlein, E., Zhao, R., Reese, T.S., Khan, S. Biophys. J. (1995) [Pubmed]
  8. Salmonella typhimurium fliG and fliN mutations causing defects in assembly, rotation, and switching of the flagellar motor. Irikura, V.M., Kihara, M., Yamaguchi, S., Sockett, H., Macnab, R.M. J. Bacteriol. (1993) [Pubmed]
  9. Structure of the bacterial flagellar hook and implication for the molecular universal joint mechanism. Samatey, F.A., Matsunami, H., Imada, K., Nagashima, S., Shaikh, T.R., Thomas, D.R., Chen, J.Z., Derosier, D.J., Kitao, A., Namba, K. Nature (2004) [Pubmed]
  10. An extreme clockwise switch bias mutation in fliG of Salmonella typhimurium and its suppression by slow-motile mutations in motA and motB. Togashi, F., Yamaguchi, S., Kihara, M., Aizawa, S.I., Macnab, R.M. J. Bacteriol. (1997) [Pubmed]
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