ZipA Is Required for Targeting of ^DMinC/DicB, but Not ^DMinC/MinD, Complexes to Septal Ring Assemblies in Escherichia coli

The MinC division inhibitor is required for accurate placement of the septal ring at the middle of the Escherichia coli cell. The N-terminal domain of MinC (^ZMinC) interferes with FtsZ assembly, while the C-terminal domain (^DMinC) mediates both dimerization and complex formation with either MinD or DicB. Binding to either of these activators greatly enhances the division-inhibitory activity of MinC in the cell. The MinD ATPase plays a crucial role in the rapid pole-to-pole oscillation of MinC that is proposed to force FtsZ ring formation to midcell. DicB is encoded by one of the cryptic prophages on the E. coli chromosome (Qin) and is normally not synthesized. Binding of MinD or DicB to ^DMinC produces complexes that have high affinities for one or more septal ring-associated targets. Here we show that the FtsZ-binding protein ZipA is required for both recruitment of the ^DMinC/DicB complex to FtsZ rings and the DicB-inducible division block normally seen in MinC⁺ cells. In contrast, none of the known FtsZ-associated factors, including ZipA, FtsA, and ZapA, appear to be specifically required for targeting of the ^DMinC/MinD complex to rings, implying that the two MinC/activator complexes must recognize distinct features of FtsZ assemblies. MinD-dependent targeting of MinC may occur in two steps of increasing topological specificity: (i) recruitment of MinC from the cytoplasm to the membrane, and (ii) specific targeting of the MinC/MinD complex to nascent septal ring assemblies on the membrane. Using membrane-tethered derivatives of MinC, we obtained evidence that both of these steps contribute to the efficiency of MinC/MinD-mediated division inhibition.