Abstract
Coordination between cell division and chromosome replication is essential for a cell to produce viable progeny. In the commonly accepted view, Escherichia coli realize this coordination via the accurate positioning of its cell division apparatus relative to the nucleoids. However, E. coli lacking proper positioning of its cell division planes can still successfully propagate. Here, we characterize how these cells partition their chromosomes into daughters during such asymmetric divisions. Using quantitative time-lapse imaging, we show that DNA translocase, FtsK, can pump as much as 80% (3.7 Mb) of the chromosome between daughters at an average rate of 1700±800 bp/s. Pauses in DNA translocation are rare, and in no occasions did we observe reversals at experimental time scales of a few minutes. The majority of DNA movement occurs at the latest stages of cell division when the cell division protein ZipA has already dissociated from the septum, and the septum has closed to a narrow channel with a diameter much smaller than the resolution limit of the microscope (~250 nm). Our data suggest that the narrow constriction is necessary for effective translocation of DNA by FtsK.
Highlights
Cell proliferation requires that each daughter cell inherits a complete set of chromosomes as a result of cell division
We show that E. coli translocase, FtsK, can move as much as 80% (3.7 Mb) of the chromosomal DNA across the closing septum in asymmetrically dividing cells at an average rate of 1700 bp/s
In Escherichia coli and most other bacteria, the assembly starts with the polymerization of FtsZ proteins into a filament network, the Z-ring, that attaches to the inner surface of the plasma membrane by ZipA and FtsA linker proteins [7,8,9,10]
Summary
Cell proliferation requires that each daughter cell inherits a complete set of chromosomes as a result of cell division. Several partially redundant mechanisms have been discovered that are responsible for the localization of the Z-ring in E. coli These mechanisms include nucleoid occlusion [2, 14], the Ter linkage [15], and the Min system [16]. Unlike nucleoid occlusion, which acts on Z-ring via negative regulation, the Ter linkage is a positive regulatory mechanism that promotes Z-ring formation near the replication terminus region of the chromosome (Ter). While nucleoid occlusion and the Ter linkage rely on the spatial organization of the chromosome in the cell, the Min system positions the Z-ring independently of the chromosome [16]. All three Z-ring localization mechanisms, i.e. SlmA, positive regulation from the Ter region, and the Min system, can be removed from E. coli without loss of cell viability [15]. Z-rings frequently localize asymmetrically relative to the nucleoid and cell centers but the cells are able to grow and divide in slow growth conditions
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