Institute for the Biotechnology of Infectious Diseases, University of Technology, Sydney, NSW 2007, Australia.
Mol Microbiol. 2010 May;76(3):634-47. doi: 10.1111/j.1365-2958.2010.07102.x. Epub 2010 Feb 28.
Although division site positioning in rod-shaped bacteria is generally believed to occur through the combined effect of nucleoid occlusion and the Min system, several lines of evidence suggest the existence of additional mechanisms. Studies using outgrown spores of Bacillus subtilis have shown that inhibiting the early stages of DNA replication, leading up to assembly of the replisome at oriC, influences Z ring positioning. Here we examine whether Z ring formation at midcell under various conditions of DNA replication inhibition is solely the result of relief of nucleoid occlusion. We show that midcell Z rings form preferentially over unreplicated nucleoids that have a bilobed morphology (lowering DNA concentration at midcell), whereas acentral Z rings form beside a single-lobed nucleoid. Remarkably however, when the DnaB replication initiation protein is inactivated midcell Z rings never form over bilobed nucleoids. Relieving nucleoid occlusion by deleting noc increased midcell Z ring frequency for all situations of DNA replication inhibition, however not to the same extent, with the DnaB-inactivated strain having the lowest frequency of midcell Z rings. We propose an additional mechanism for Z ring positioning in which the division site becomes increasingly potentiated for Z ring formation as initiation of replication is progressively completed.
尽管杆状细菌的分裂位点定位通常被认为是通过核区阻断和 Min 系统的联合作用发生的，但有几条证据表明存在其他机制。使用枯草芽孢杆菌长出的孢子进行的研究表明，抑制 DNA 复制的早期阶段，导致复制起始点 oriC 处复制体的组装，会影响 Z 环的定位。在这里，我们研究了在各种 DNA 复制抑制条件下，中膜处 Z 环的形成是否仅仅是核区阻断缓解的结果。我们表明，在降低中膜处 DNA 浓度的情况下（形成具有双叶形态的未复制核区），中膜处 Z 环优先形成，而在单个叶状核区旁边形成中央 Z 环。然而，令人惊讶的是，当 DNA 复制起始蛋白 DnaB 失活时，中膜处 Z 环从不形成于双叶状核区。通过删除 noc 来缓解核区阻断，增加了所有 DNA 复制抑制情况下的中膜 Z 环频率，但程度不同，DnaB 失活菌株的中膜 Z 环频率最低。我们提出了一种用于 Z 环定位的额外机制，其中随着复制起始的逐步完成，分裂位点对于 Z 环形成的潜力逐渐增强。
