Total reconstitution of Salmonella flagellar filaments from hook and purified flagellin and hook-associated proteins in vitro.

Salmonella flagellar filaments comprise the following distinct parts connected in series: a curved hook composed of a single kind of subunit (hook protein); two short segments made up of hook-associated proteins (HAP1 and HAP3); a long helical filament composed of flagellin; and a cap composed of HAP2. In this study, a procedure was developed to isolate HAPs from the culture medium of a short-flagella mutant. We demonstrate that hook-filament complex can be formed in vitro by sequential addition of HAP1, HAP3 and flagellin to hook fragments.