FIG 6.

Working model of MS-ring assembly regulated by the FliG, FlhF, and FlhG proteins. (A) FlhF may interact with a nascent FliF polypeptide chain and conduct the nascent chain to the Sec translocon machinery to insert FliF into the cytoplasmic membrane with appropriate topology. However, we have no evidence to prove that the FliF protein is inserted into the cytoplasmic membrane via the Sec translocon. FlhG may affect FlhF function and/or interact with FliF to inhibit the insertion. (B) FlhF may directly interact with an FliF molecule to recruit it to the cell pole and facilitate MS-ring formation at the cell pole. FliG interacts with the C-terminal region of FliF, and FliF and FliG form a complex. FliF and FliG assist in each other’s assembly into the MS-ring and C-ring. FlhG may indirectly affect FlhF function.