CELL CYCLE-CONTROLLED PROTEOLYSIS OF A FLAGELLAR MOTOR PROTEIN THAT IS ASYMMETRICALLY DISTRIBUTED IN THE CAULOBACTER PREDIVISIONAL CELL

Flagellar biogenesis and release are developmental events tightly coup led to the cell cycle of Caulobacter crescentus. A single flagellum is assembled at the swarmer pole of the predivisionaI cell and is releas ed later in the cell cycle. Here we show that the MS-ring monomer FLiF , a central motor component that anchors the flagellum in the cell mem brane, is synthesized only in the predivisional cell and is integrated into the membrane at the incipient swarmer cell pole, where it initia tes fIagellar assembly, FliF is proteolytically turned over during swa rmer-to-stalked cell differentiation, coinciding with the loss of the flagellum, suggesting that its degradation is coupled to flagellar rel ease, The membrane topology of FLiF was determined and a region of the cytoplasmic C-terminal domain was shown to be required for the intera ction with a component of the motor switch. The very C-terminal end of FliF contains a turnover determinant, required for the cell cycle-dep endent degradation of the MS-ring. The cell cycle-dependent proteolysi s of FliF and the targeting of FliF to the swarmer pole together contr ibute to the asymmetric localization of the MS-ring in the predivision al cell.