Affiliation:
1. Department of Microbiology, University of Georgia, Athens, Georgia, USA
Abstract
ABSTRACT
Flagellar biogenesis in
Helicobacter pylori
is regulated by a transcriptional hierarchy governed by three sigma factors, RpoD (σ
80
), RpoN (σ
54
), and FliA (σ
28
), that temporally coordinates gene expression with the assembly of the flagellum. Previous studies showed that loss of flagellar protein export apparatus components inhibits transcription of flagellar genes. The FlgS/FlgR two-component system activates transcription of RpoN-dependent genes though an unknown mechanism. To understand better the extent to which flagellar gene regulation is coupled to flagellar assembly, we disrupted flagellar biogenesis at various points and determined how these mutations affected transcription of RpoN-dependent (
flaB
and
flgE
) and FliA-dependent (
flaA
) genes. The MS ring (encoded by
fliF
) is one of the earliest flagellar structures assembled. Deletion of
fliF
resulted in the elimination of RpoN-dependent transcripts and an ∼4-fold decrease in
flaA
transcript levels. FliH is a cytoplasmic protein that functions with the C ring protein FliN to shuttle substrates to the export apparatus. Deletions of
fliH
and genes encoding C ring components (
fliM
and
fliY
) decreased transcript levels of
flaB
and
flgE
but had little or no effect on transcript levels of
flaA
. Transcript levels of
flaB
and
flgE
were elevated in mutants where genes encoding rod proteins (
fliE
and
flgBC
) were deleted, while transcript levels of
flaA
was reduced ∼2-fold in both mutants. We propose that FlgS responds to an assembly checkpoint associated with the export apparatus and that FliH and one or more C ring component assist FlgS in engaging this flagellar structure.
IMPORTANCE
The mechanisms used by bacteria to couple transcription of flagellar genes with assembly of the flagellum are poorly understood. The results from this study identified components of the
H. pylori
flagellar basal body that either positively or negatively affect expression of RpoN-dependent flagellar genes. Some of these basal body proteins may interact directly with regulatory proteins that control transcription of the
H. pylori
RpoN regulon, a hypothesis that can be tested by examining protein-protein interactions
in vitro
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Reference52 articles.
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5. The FliN−FliH Interaction Mediates Localization of Flagellar Export ATPase FliI to the C Ring Complex
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