Männik Jaana, Bailey Matthew W, O'Neill Jordan C, Männik Jaan
Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, United States of America.
Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, United States of America.
PLoS Genet. 2017 Feb 24;13(2):e1006638. doi: 10.1371/journal.pgen.1006638. eCollection 2017 Feb.
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.
细胞分裂与染色体复制之间的协调对于细胞产生可存活的后代至关重要。在普遍接受的观点中，大肠杆菌通过其细胞分裂装置相对于类核的准确定位来实现这种协调。然而，细胞分裂平面定位不当的大肠杆菌仍能成功繁殖。在此，我们描述了这些细胞在这种不对称分裂过程中如何将其染色体分配到子细胞中。使用定量延时成像，我们发现DNA转位酶FtsK能够以平均1700±800 bp/s的速率在子细胞之间泵送多达80%（3.7 Mb）的染色体。DNA转位过程中的停顿很少见，在几分钟的实验时间尺度内，我们从未观察到反转现象。大多数DNA移动发生在细胞分裂的最后阶段，此时细胞分裂蛋白ZipA已经从隔膜上解离，隔膜已闭合形成一个直径远小于显微镜分辨率极限（约250 nm）的狭窄通道。我们的数据表明，狭窄的收缩对于FtsK有效转运DNA是必要的。
