| Bacterial flagellar basal bodies isolated using standard protocols do not possess the proteins required for motor function. Five motor proteins have been identified to date based on genetic analysis in Escherichia coli and Salmonella typhimurium. Two of these, MotA and MotB are required for motor rotation only. These form a transmembrane complex. Three others, FliG, FliM and FliN are all required not only for motor rotation but also for flagellar synthesis and switching. These have been postulated to form a cytoplasmically based structural complex. In this study, novel bell-like cytoplasmic flagellar basal structures were revealed upon electron microscopic examination of freeze-substituted preparations of cytoplasm-free bacterial cell envelopes. An isolation protocol was then developed that has enabled routine preparations of flagella possessing such basal structures. Once isolated, these structures dissociated rapidly under various conditions. Their lability was exploited in examining the basal bodies from point mutants of fliG, fliM and fliN genes. In mutants with lesions giving rise to paralysed flagella (... |
