Accurate placement of the division septum at the midpoint of Escherichia coli cells requires the combined action of a general division inhibitor (MinC), a site-specific suppressor of division inhibition (MinE), and an ATPase (MinD) that is required for proper functioning of both MinC and MinE. We previously showed that a functional MinE-Gfp fusion accumulates in a ring structure at͞near the middle of cells. Here we show that functional Gfp-MinD accumulates alternately in either one of the cell halves in what appears to be a rapidly oscillating membrane association-dissociation cycle imposed by MinE. The results indicate that MinD represents a novel type of dynamic cellular element in bacteria, with multiple roles in directing the division apparatus to the middle of the cell.

E. coli cell division is mediated by the FtsZ ring and associated factors. Selection of the correct division site requires the combined action of an inhibitor of FtsZ ring formation (MinCD) and of a topological specificity factor that somehow prevents MinCD action at the middle of the cell (MinE). Here we show that a biologically active MinE-Gfp fusion accumulates in an annular structure near the middle of young cells. Formation of the MinE ring required MinD but was independent of MinC and continued in nondividing cells in which FtsZ function was inhibited. The results indicate that the MinE ring represents a novel cell structure, which allows FtsZ ring formation at midcell by suppressing MinCD activity at this site.

By inhibiting FtsZ ring formation near the cell ends, the MinC protein plays a critical role in proper positioning of the division apparatus in Escherichia coli. MinC activity requires that of MinD, and the MinE peptide provides topological specificity by suppressing MinC-MinD-mediated division inhibition specifically at the middle of the cell. We recently presented evidence that MinE not only accumulates in an FtsZ-independent ring structure at the cell’s middle but also imposes a unique dynamic localization pattern upon MinD in which the latter accumulates alternately in either one of the cell halves in what appears to be a rapidly oscillating membrane association-dissociation cycle. Here we show that functional green fluorescent protein-MinC displays a very similar oscillatory behavior which is dependent on both MinD and MinE and independent of FtsZ. The results support a model in which MinD recruits MinC to its site of action and in which FtsZ ring assembly at each of the cell ends is blocked in an intermittent and alternate fashion.