Abstract
The bacterial flagellum is unique among Nature's motors in that it posesses a reversible, rotary motor and a propeller that converts torque into thrust The basal body, that part of the flagellum isolated from cells in attempts to purify the motor, contains eight different structural proteins. In Salmonella typhimurimi, the basal body consists of four rings (denoted M, S, L, and P) threaded on a coaxial rod. The M-S, L and Prings are each composed of a different protein, FliF, FlgH, and Flgl, each of which is present in ∽26 copies. The rod contains four different proteins, FlgB, FlgC, FlgF, and FlgG. Also present is FliE. These all are present in ∽6 copies except for FlgG present in ∽26 copies. The proteins important for motor rotation, however, are missing in standard basal body preparations. These missing proteins include the three “switch” proteins, FliG, FliM, and FliN, which control motor reversal (clockwise and counter-clockwise rotation) and may correspond to the rotor and gearbox of the motor. FliG has recently been shown to be localized at the M ring.