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Journal of Bacteriology, July 2008, p. 4979-4988, Vol. 190, No. 14
0021-9193/08/$08.00+0     doi:10.1128/JB.01996-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

FliZ Is a Posttranslational Activator of FlhD4C2-Dependent Flagellar Gene Expression{triangledown}

Supreet Saini,1 Jonathon D. Brown,2,3 Phillip D. Aldridge,2,3* and Christopher V. Rao1*

Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801,1 Centre for Bacterial Cell Biology, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, United Kingdom,2 Institute for Cell and Molecular Biosciences, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, United Kingdom3

Received 21 December 2007/ Accepted 28 April 2008

Flagellar assembly proceeds in a sequential manner, beginning at the base and concluding with the filament. A critical aspect of assembly is that gene expression is coupled to assembly. When cells transition from a nonflagellated to a flagellated state, gene expression is sequential, reflecting the manner in which the flagellum is made. A key mechanism for establishing this temporal hierarchy is the {sigma}28-FlgM checkpoint, which couples the expression of late flagellar (Pclass3) genes to the completion of the hook-basal body. In this work, we investigated the role of FliZ in coupling middle flagellar (Pclass2) gene expression to assembly in Salmonella enterica serovar Typhimurium. We demonstrate that FliZ is an FlhD4C2-dependent activator of Pclass2/middle gene expression. Our results suggest that FliZ regulates the concentration of FlhD4C2 posttranslationally. We also demonstrate that FliZ functions independently of the flagellum-specific sigma factor {sigma}28 and the filament-cap chaperone/FlhD4C2 inhibitor FliT. Furthermore, we show that the previously described ability of {sigma}28 to activate Pclass2/middle gene expression is, in fact, due to FliZ, as both are expressed from the same overlapping Pclass2 and Pclass3 promoters at the fliAZY locus. We conclude by discussing the role of FliZ regulation with respect to flagellar biosynthesis based on our characterization of gene expression and FliZ's role in swimming and swarming motility.

* Corresponding author. Mailing address for Christopher V. Rao: Department of Chemical and Biomolecular Engineering. University of Illinois at Urbana-Champaign, 600 S. Mathews Ave., Urbana, IL 61810. Phone: (217) 244-2247. Fax: (217) 333-5052. E-mail: chris{at}scs.uiuc.edu. Mailing address for Phillip D. Aldridge: Centre for Bacterial Cell Biology, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, United Kingdom. Phone: 44-191-222-7704. Fax: 44-191-222-7424. E-mail: p.d.aldridge{at}ncl.ac.uk

{triangledown} Published ahead of print on 9 May 2008.

Journal of Bacteriology, July 2008, p. 4979-4988, Vol. 190, No. 14
0021-9193/08/$08.00+0     doi:10.1128/JB.01996-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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