HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Supplementary data Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Smith, T. G. Articles by Hoover, T. R. Search for Related Content PubMed PubMed Citation Articles by Smith, T. G. Articles by Hoover, T. R. Agricola Articles by Smith, T. G. Articles by Hoover, T. R.

Helicobacter pylori FlhB processing-deficient variants affect flagellar assembly but not flagellar gene expression

¹ Department of Microbiology, University of Georgia, Athens, GA 30602, USA
² Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA

Correspondence
Timothy R. Hoover
trhoover{at}uga.edu

Regulation of the Helicobacter pylori flagellar gene cascade involves the transcription factors ⁵⁴ (RpoN), employed for expression of genes required midway through flagellar assembly, and ²⁸ (FliA), required for expression of late genes. Previous studies revealed that mutations in genes encoding components of the flagellar protein export apparatus block expression of the H. pylori RpoN and FliA regulons. FlhB is a membrane-bound component of the export apparatus that possesses a large cytoplasmic domain (FlhB_C). The hook length control protein FliK interacts with FlhB_C to modulate the substrate specificity of the export apparatus. FlhB_C undergoes autocleavage as part of the switch in substrate specificity. Consistent with previous reports, deletion of flhB in H. pylori interfered with expression of RpoN-dependent reporter genes, while deletion of fliK stimulated expression of these reporter genes. In the flhB mutant, disrupting fliK did not restore expression of RpoN-dependent reporter genes, suggesting that the inhibitory effect of the flhB mutation is not due to the inability to export FliK. Amino acid substitutions (N265A and P266G) at the putative autocleavage site of H. pylori FlhB prevented processing of FlhB and export of filament-type substrates. The FlhB variants supported wild-type expression of RpoN- and FliA-dependent reporter genes. In the strain producing FlhB^N265A, expression of RpoN- and FliA-dependent reporter genes was inhibited when fliK was disrupted. In contrast, expression of these reporter genes was unaffected or slightly stimulated when fliK was disrupted in the strain producing FlhB^P266G. H. pylori HP1575 (FlhX) shares homology with the C-terminal portion of FlhB_C (FlhB_CC) and can substitute for FlhB_CC in flagellar assembly. Disrupting flhX inhibited expression of a flaB reporter gene in the wild-type but not in the fliK mutant or strains producing FlhB variants, suggesting a role for FlhX or FlhB_CC in normal expression of the RpoN regulon. Taken together, these data indicate that the mechanism by which the flagellar protein export apparatus exerts control over the H. pylori RpoN regulon is complex and involves more than simply switching substrate specificity of the flagellar protein export apparatus.

A supplementary table listing oligonucleotide primers used in this study is available with the online version of this paper.