Recruitment of ZipA to the septal ring of Escherichia coli is dependent onFtsZ and independent of FtsA

Cell division in prokaryotes is mediated by the septal ring. In Escherichia coli, this organelle consists of several essential division proteins, incl uding FtsZ, FtsA, and ZipA. To gain more insight into how the structure is assembled, we studied the interdependence of FtsZ, FtsA, and ZipA localizat ion using both immunofluorescence and Gfp tagging techniques. To this end, we constructed a set of strains allowing us to determine the cellular locat ion of each of these three proteins in cells from which one of the other tw o had been specifically depleted. Our results show that ZipA fails to accum ulate in a ring shape in the absence of FtsZ. Conversely, depletion of ZipA does not abolish formation of FtsZ rings but leads to a significant reduct ion in the number of rings per unit of cell mass. In addition, ZipA does no t appear to require FtsA for assembly into the septal ring and vice versa, It is suggested that septal ring formation starts by assembly of the FtsZ r ing, after which ZipA and FtsA join this structure in a mutually independen t fashion through direct interactions with the FtsZ protein.