SummaryThree membrane proteins required for cell division in Escherichia coli , FtsQ, FtsL and FtsB, localize to the cell septum. FtsL and FtsB, which each contain a leucine zipper-like sequence, are dependent on each other for this localization, and each of them is dependent on FtsQ. However, FtsQ is found at the cell division site in the absence of FtsL and FtsB. FtsQ, in turn, requires FtsK for its localization. Here, we show that FtsL, FtsB and FtsQ form a complex in vivo . Strikingly, this complex forms in the absence of FtsK, which is required for the localization of all three proteins to the mid-cell. These findings indicate that the FtsL, FtsB, FtsQ interactions can take place in cells before movement to the mid-cell and that migration to this position might occur only after the formation of the complex. Evidence indicating the regions of the three proteins involved in complex formation is presented. These findings provide the first example of preassembly of a subcomplex of cell division proteins before their localization to the septal region.

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One-sentence summary: This review highlights recent findings on the mechanism by which proteins are lipidated and discusses the enzymes involved, substrate specificities among bacterial species and the role of lipoprotein modification in the biogenesis of the cell envelope. Editor: Mecky Pohlschroder ABSTRACTPosttranslational modification of proteins by lipidation is a common process in biological systems. Lipids provide protein stability, interaction with other membrane components, and in some cases, due to reversibility of the process, a mechanism for regulating protein localization and function. Bacterial lipoproteins possess fatty acids at their amino-termini that are derived from phospholipids, and this lipid moiety anchors the proteins into the membrane. These lipids, as is the case for lipopolysaccharides and lipoteichoic acids, play an important role in signaling of the innate immune system through the interaction with Toll-like receptors. Over the past three years, tremendous progress has been made in understanding the mechanism by which lipoproteins become lipidated. Advanced methodology in mass spectrometry, proteomics and genome-wide analyses allowed precise characterization of lipoprotein modifications and the identification of the enzymes catalyzing the reactions in diverse bacterial species. This review will highlight new findings on bacterial lipoprotein modification with focus on the reaction mechanisms and the role of lipoproteins in cell envelope homeostasis.

The timing of the appearance of the FtsZ ring at the future site of division in Escherichia coli was determined by in situ immunofluorescence microscopy for two strains grown under steady-state conditions. The strains, B/rA and K-12 MC4100, differ largely in the duration of the D period, the time between termination of DNA replication and cell division. In both strains and under various growth conditions, the assembly of the FtsZ ring was initiated approximately simultaneously with the start of the D period. This is well before nucleoid separation or initiation of constriction as determined by fluorescence and phase-contrast microscopy. The durations of the Z-ring period, the D period, and the period with a visible constriction seem to be correlated under all investigated growth conditions in these strains. These results suggest that (near) termination of DNA replication could provide a signal that initiates the process of cell division.