We study the interactions between the MS-ring and other basal body proteins of the bacterial flagellum of Salmonella typhimurium. We also study the functions of the switch proteins, espetially FliM.
Flagellar assembly starts from the formation of the MS-ring composed of many copies of FliF. The previous analysis of a fliF mutant, SJW3060, which easily releases its flagellar filaments into viscous media showed that one of the rod proteins, FlgG, was found attached to the released filament. This suggested that there are some interactions between the MS-ring and FlgG. To analyze the interactions between the MS-ring and other basal body proteins, we have been conducting chacterization of the revertants from SJW3060. So far, sequencing of revertants mapped on region I is completed, and their mutaion sites have been found in rod ptoteins (FlgC and FlgF). The results suggest significant interactions between the MS ring and the rod proteins. Characterization of the region II revertants is underway.
     FliM is a component of the flagellar switch complex. The detailed role of FliM is not known. Overproduction of FliM results in inclusion body, which causes difficulties in its purification and characterization. Therefore, we have constructed plasmids for the expression of several types of FliM fragments. Characterization of these mutant FliM is now underway.