ZapA and ZapB form an FtsZ-independent structure at midcell

SUMMARY

Cell division in Escherichia coli begins with the polymerization of FtsZ into a ring-like structure, the Z-ring, at midcell. All other division proteins are thought to require the Z-ring for recruitment to the future division site. Here, we report that the Z-ring associated proteins ZapA and ZapB form FtsZ-independent structures at midcell. Upon Z-ring disruption by the FtsZ polymerization antagonist SulA, ZapA remained at midcell as a cloud-like accumulation. Using ZapA(N60Y), a variant defective for interaction with FtsZ, it was established that these ZapA structures form without a connection to the Z-ring. Furthermore, midcell accumulations of GFP-ZapA(N60Y) often preceded Z-rings at midcell and required ZapB to assemble, suggesting that ZapB polymers form the foundation of these structures. In the absence of MatP, a DNA-binding protein that links ZapB to the chromosomal terminus region, cloud-like ZapA structures still formed but failed to track with the chromosome terminus and did not consistently precede FtsZ at midcell. Taken together, our results suggest that FtsZ-independent structures of ZapA-ZapB provide additional positional cues for Z-ring formation and may help coordinate its assembly with chromosome replication and segregation.

Graphical abstract

We found that E. coli’s FtsZ-ring associated protein ZapA forms FtsZ-independent structures at midcell that are dependent on ZapB. Furthermore, these ZapA-ZapB structures are capable of identifying new sites of division prior to polymerization of the FtsZ-ring and this phenomenon is largely dependent on the ter-binding protein, MatP. Taken together, our results suggest that FtsZ-independent structures of ZapA-ZapB provide additional positional cues for FtsZ-ring formation and may help coordinate its assembly with chromosome replication and segregation.