Present address: Institute of Cell and Molecular Biosciences, The Medical School, University of Newcastle, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK.
Flk prevents premature secretion of the anti-σ factor FlgM into the periplasm
Article first published online: 8 MAR 2006
Volume 60, Issue 3, pages 630–643, May 2006
How to Cite
Aldridge, P., Karlinsey, J. E., Becker, E., Chevance, F. F.V. and Hughes, K. T. (2006), Flk prevents premature secretion of the anti-σ factor FlgM into the periplasm. Molecular Microbiology, 60: 630–643. doi: 10.1111/j.1365-2958.2006.05135.x
- Issue published online: 8 MAR 2006
- Article first published online: 8 MAR 2006
- Accepted 16 February, 2006.
Vol. 61, Issue 1, 269, Article first published online: 9 MAY 2006
The flk locus of Salmonella typhimurium was identified as a regulator of flagellar gene expression in strains defective in P- and l-ring formation. Flk acts as a regulator of flagellar gene expression by modulating the protein levels of the anti-σ28 factor FlgM. Evidence is presented which suggests that Flk is a cytoplasmic-facing protein anchored to the inner membrane by a single, C-terminal transmembrane-spanning domain (TMS). The specific amino acid sequence of the TMS is not essential for Flk activity, but membrane anchoring is essential. Membrane fractionation and visualization of protein fusions of green fluorescent protein derivatives to Flk suggested that the Flk protein is present in the membrane as punctate spots in number that are much greater than the number of flagellar basal structures. The turnover of the anti-σ28 factor FlgM was increased in flk mutant strains. Using FlgM–β-lactamase fusions we show the increased turnover of FlgM in flk null mutations is due to FlgM secretion into the periplasm where it is degraded. Our data suggest that Flk inhibits FlgM secretion by acting as a braking system for the flagellar-associated type III secretion system. A model is presented to explain a role for Flk in flagellar assembly and gene regulatory processes.