MinC mutants deficient in MinD- and DicB-mediated cell division inhibition due to loss of interaction with MinD, DicB, or a septal component.

The min locus encodes a negative regulatory system that limits formation of the cytokinetic Z ring to midcell by preventing its formation near the poles. Of the three Min proteins, MinC is the inhibitor and prevents Z-ring formation by interacting directly with FtsZ. MinD activates MinC by recruiting it to the membrane and conferring a higher affinity on the MinCD complex for a septal component. MinE regulates the cellular location of MinCD by inducing MinD, and thereby MinC, to oscillate between the poles of the cell, resulting in a time-averaged concentration of MinCD on the membrane that is lowest at midcell. MinC can also be activated by the prophage-encoded protein DicB, which targets MinC to the septum without recruiting it first to the membrane. Previous studies have shown that the C-terminal domain of MinC is responsible for the interaction with MinD, DicB, and the septal component. In the present study, we isolated mutations in the C-terminal domain of MinC that affected its interaction with MinD, DicB, and the septal component. Among the mutations isolated, R133A and S134A are specifically deficient in the interaction with MinD, E156A is primarily affected in the interaction with DicB, and R172A is primarily deficient in the interaction with the septum. These mutations differentiate the interactions of MinC with its partners and further support the model of MinCD- and MinC-DicB-mediated cell division inhibition.