N-terminal signal region of FliK is dispensable for length control of the flagellar hook.
The length of the flagellar hook is regulated; it is 55 +/- 6 nm long in Salmonella. Five genes involved in hook-length regulation are fliK, flhB, fliG, fliM and fliN. The last four genes encode structural components of the protein export apparatus in the flagellar base, whereas FliK is soluble and secreted during flagellar assembly. The role of FliK, however, remains ambiguous. We constructed two kinds of FliK variants: N-terminally truncated FliK protein and FliK N-terminally fused with cyan fluorescent protein (CFP-FliK). Both N-terminally truncated FliK missing the first 99 amino acids (aa) and CFP-FliK fusion variants partially complemented a fliK null (polyhook) mutant to produce cells with filaments, allowing cells to swim; the hooks, however, were not normal but were polyhooks. When the N-terminally defective FliK variants were expressed at high levels, the average polyhook length was shortened coming close to the length of the wild-type hook, independently of the sizes of the FliK variants. These FliK variants were not secreted. CFP-FliK fusion proteins were observed to homogeneously distribute in the cytoplasm. We conclude that FliK does not need to be exported to control hook length and is unlikely to be a ruler; instead, we conclude that FliK controls hook length by the timely switching of secretion modes of the flagellar type III secretion system by the FliK C-terminal domain, and that the N-terminal region is dispensable for hook length control.
Hirano
Takanori
T
CREST, Japan Science and Technology Agency (JST), 1064-18 Takahori, Hirata, Takanezawa, Shioya-gun, Tochigi 329-1206, Japan.
Shibata
Satoshi
S
Ohnishi
Kouhei
K
Tani
Tomomi
T
Aizawa
Shin-Ichi
S
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D005407:Flagella / Q000502:physiology*; D009154:Mutation; D021382:Protein Sorting Signals / Q000502:physiology*; D012475:Salmonella / Q000502:physiology* / Q000648:ultrastructure; D015398:Signal Transduction
D001426:Bacterial Proteins; C099487:FliK protein, Salmonella; D021382:Protein Sorting Signals