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Journal of Bacteriology, August 2000, p. 4207-4215, Vol. 182, No. 15
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Role of FliJ in Flagellar Protein Export in Salmonella

Tohru Minamino,1,dagger Ryan Chu,1 Shigeru Yamaguchi,2 and Robert M. Macnab1,*

Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114,1 and Izumi Campus, Meiji University, Suginami, Tokyo 168-0064, Japan2

Received 29 February 2000/Accepted 15 May 2000

We isolated and characterized spontaneous mutants with defects in the 147-amino-acid Salmonella protein FliJ, which is a cytoplasmic component of the type III flagellar export apparatus. These mutants, including ones with null mutations, have the ability to form swarms on motility agar plates after prolonged incubation at 30°C; i.e., they display a leaky motile phenotype. One mutant, SJW277, which formed significantly bigger swarms than the others, encoded only the N-terminal 73 amino acids of FliJ, one-half of the protein. At 30°C, overproduction of this mutant protein improved, to wild-type levels, both motility and the ability to export both rod/hook-type (FlgD; hook capping protein) and filament-type (FliC; flagellin) substrates. At 42°C, however, export was inhibited, indicating that the mutant FliJ protein was temperature sensitive. Taking advantage of this, we performed temperature upshift experiments, which demonstrated that FliJ is directly required for the export of FliC. Co-overproduction of FliJ and either of two export substrates, FliE or FlgG, hindered their aggregation in the cytoplasm. We conclude that FliJ is a general component of the flagellar export apparatus and has a chaperone-like activity for both rod/hook-type and filament-type substrates.

* Corresponding author. Mailing address: Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114. Phone: (203) 432-5590. Fax: (203) 432-9782. E-mail: robert.macnab{at}yale.edu.

dagger Present address: International Institute for Advanced Research, Matsushita Electric Industrial Company, Ltd., 1-7 Hikaridai, Seika, Kyoto, 619-0237, Japan.

Journal of Bacteriology, August 2000, p. 4207-4215, Vol. 182, No. 15
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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