Fig. 6.

Model for preseptal PG synthesis in the presence or absence of ZipA. FtsZ, ZipA and either PBP1A or PBP1B are essential for preseptal PG synthesis. The cytosolic FtsZ ring (Z-ring) and the PG synthases are linked at early stages of cell division by ZipA and by FtsA-FtsN. ZipA promotes monomerization of FtsA, which is needed to obtain the FtsA–FtsN complex. In the presence of FtsA* (FtsA mutants impaired in dimerisation) the interaction between FtsA* and FtsN is enhanced, rendering ZipA dispensable and FtsN essential to link the Z-ring and the PG synthesis machinery. In the absence of FtsN, ZipA becomes the only linker between both cytosolic and periplasmic proteins. When both ZipA and FtsN are absent the link is lost, leading to non-viable cells. The cell membrane is not shown in this diagram