FIG. 1.
Division site selection in rod-shaped bacteria. (A) Roles of nucleoid occlusion and the Min system. In cells that are about to divide, the correct midcell division site is chosen by the combined action of two negative regulatory systems. The localization of the two nucleoids blocks division in their vicinity, as shown, leaving spaces available for division at the correct midcell site and at the cell poles. The Min system acts to prevent incorrect division at the cell poles. (B) Blocking division at the cell poles. The MinCD inhibitor associates with the cytoplasmic membrane at the cell poles and prevents FtsZ polymerization. The C-terminal domain of MinC (CC) ensures MinC dimerization and interacts with MinD (D), which in turn associates with the membrane. The N-terminal domain of MinC (CN) interacts with FtsZ (Z) and prevents polymerization of FtsZ or interaction of other cell division proteins with the FtsZ ring (see the text). The MinD-MinC stoichiometry, and the presumed action of MinC, preventing the formation of correct FtsZ interactions remains hypothetical. (C and D) Contrasting functioning of the Min system in E. coli (C) and B. subtilis (D). MinD (chevrons [ATP form] and rectangles [ADP form]) is postulated to polymerize in the presence of ATP. In E. coli (A), it forms dynamic filaments emanating from one cell pole. A ring of MinE proteins associates with the ends of the filaments and moves in a poleward manner, by interaction with the MinD filaments. MinE stimulates hydrolysis of ATP by MinD, and this results in the release of monomers, probably following a conformational change (rectangles), which enter the cytoplasm. After exchange of the ADP for ATP, MinD polymers can re-form at the opposite cell pole, possibly requiring a nucleation site at the pole. In B. subtilis (B), MinD forms static filaments restricted to the polar zones as a result of nucleation by DivIVA protein targeted to the cell poles (black triangles). In both cases, MinD is associated with the division inhibitor (MinC; not shown), which blocks Z ring formation. Reproduced reference 8 with permission from the publisher.