SENSING STRUCTURAL INTERMEDIATES IN BACTERIAL FLAGELLAR ASSEMBLY BY EXPORT OF A NEGATIVE REGULATOR

The ability of a regulatory protein to sense the integrity of the bact erial flagellar structure was investigated. In response to a defective hook-basal body complex, the anti-sigma(28) FlgM protein inhibits fla gellin transcription. In cells with a functional hook-basal body compl ex, the flagellin genes are transcribed normally and the FlgM protein is expelled into the growth medium. In strains with a defective hook-b asal body structure, FlgM is absent from the media. The presence of fl agellin protein in the media is substantially reduced in strains carry ing a FlgM-LacZ protein fusion, suggesting that the fusion is blocking the flagellar export apparatus. These results suggest that the FlgM p rotein assesses the integrity of the flagellar hook-basal body complex by itself being a substrate for export by the flagellar-specific expo rt apparatus.