AMINO-ACIDS RESPONSIBLE FOR FLAGELLAR SHAPE ARE DISTRIBUTED IN TERMINAL REGIONS OF FLAGELLIN

The shape of the flagellar filaments of the bacterium Salmonella typhimurium, under ordinary conditions is a left-handed helix. In addition to the normal wild-type filament, non-helical (i.e. straight), right-handed helical (curly), or circular (semi-coiled and coiled) filaments and filament with small amplitude (f1-type) have been found in mutants or in filaments reconstituted in vitro. We analysed wild-type flagellin and flagellins from 17 flagellar-shape mutants (6 with straight filaments, 6 with curly filaments, 4 with coiled filaments and 1 with f1-type filament) by amino acid sequencing to identify the mutational sites. All mutant flagellins except that of the f1-type filament had single mutations; the f1-type flagellin had two mutations in the molecule. The sites of these mutations were localized in α-helical segments of the terminal regions of flagellin. A possible mechanism of the polymorphism of the flagellar filament is discussed. © 1991.