Journal of Bacteriology, February 2006, p. 958-967, Vol. 188, No. 3
0021-9193/06/$08.00+0 doi:10.1128/JB.188.3.958-967.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
FljA-Mediated Posttranscriptional Control of Phase 1 Flagellin Expression in Flagellar Phase Variation of Salmonella enterica Serovar Typhimurium
Shouji Yamamoto1 and
Kazuhiro Kutsukake1,2*
Graduate School of Natural Science and Technology,1
Department of Biology, Faculty of Science, Okayama University, Tsushima-Naka 3-1-1, Okayama 700-8530, Japan2
Received 13 September 2005/
Accepted 7 November 2005
Flagellar phase variation of Salmonella is a phenomenon where two flagellin genes, fliC (phase 1) and fljB (phase 2), are expressed alternately. This is controlled by the inversion of a DNA segment containing the promoter for the fljB gene. The fljB gene constitutes an operon with the fljA gene, which encodes a negative regulator for fliC expression. Previous biochemical analysis suggested that phase variation might depend on alternative synthesis of phase-specific flagellin mRNA (H. Suzuki and T. Iino, J. Mol. Biol. 81:57-70, 1973). However, recently reported results suggested that FljA-dependent inhibition might be mediated by a posttranscriptional control mechanism (H. R. Bonifield and K. T. Hughes, J. Bacteriol. 185:3567-3574, 2003). In this study, we reexamined the mechanism of FljA-mediated inhibition of fliC expression more carefully. Northern blotting analysis revealed that no fliC mRNA was detected in phase 2 cells. However, only a moderate decrease in ß-galactosidase activity was observed from the fliC-lacZ transcriptional fusion gene in phase 2 cells compared with that in phase 1 cells. In contrast, the expression of the fliC-lacZ translational fusion gene was severely impaired in phase 2 cells. The half-life of fliC mRNA was shown to be much shorter in phase 2 cells than in phase 1 cells. Purified His-tagged FljA protein was shown to bind specifically to fliC mRNA and inhibit the translation from fliC mRNA in vitro. On the basis of these results, we propose that in phase 2 cells, FljA binds to fliC mRNA and inhibits its translation, which in turn facilitates its degradation.
* Corresponding author. Mailing address: Department of Biology, Faculty of Science, Okayama University, Tsushima-Naka 3-1-1, Okayama 700-8530, Japan. Phone: 81-86-251-7863. Fax: 81-86-251-7876. E-mail: ktkk{at}cc.okayama-u.ac.jp.
Journal of Bacteriology, February 2006, p. 958-967, Vol. 188, No. 3
0021-9193/06/$08.00+0 doi:10.1128/JB.188.3.958-967.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
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Copyright © 2006 by the American Society for Microbiology. All rights reserved.