FtsQ, FtsL and FtsI require FtsK, but not FtsN, for co-localization with FtsZ during Escherichia coli cell division

During cell division in Gram-negative bacteria, the cell envelope invaginat es and constricts at the septum, eventually severing the cell into two comp artments, and separating the replicated genetic materials. In Escherichia c oli, at least nine essential gene products participate directly in septum f ormation: FtsA, FtsI, FtsL, FtsK, FtsN, FtsQ, FtsW, FtsZ and ZipA. All nine proteins have been localized to the septal ring, an equatorial ring struct ure at the division site. We used translational fusions to green fluorescen t protein (GFP) to demonstrate that FtsQ, FtsL and FtsI localize to potenti al division sites in filamentous cells depleted of FtsN, but not in those d epleted of FtsK. We also constructed translational fusions of FtsZ, FtsA, F tsQ, FtsL and FtsI to enhanced cyan or yellow fluorescent protein (ECFP or EYFP respectively), GFP variants with different fluorescence spectra. Exami nation of cells expressing different combinations of the fusions indicated that FtsA, FtsQ, FtsL and FtsI colocalize with FtsZ in filaments depleted o f FtsN. These localization results support the model that E. coli cell divi sion proteins assemble sequentially as a multimeric complex at the division site: first FtsZ, then FtsA and ZipA independently of each other, followed successively by FtsK, FtsQ, FtsL, FtsW, FtsI and FtsN.