Adams David William, Wu Ling Juan, Errington Jeff
Centre for Bacterial Cell Biology, Medical School, Newcastle University, Newcastle Upon Tyne, UK.
Centre for Bacterial Cell Biology, Medical School, Newcastle University, Newcastle Upon Tyne, UK
EMBO J. 2015 Feb 12;34(4):491-501. doi: 10.15252/embj.201490177. Epub 2015 Jan 7.
To proliferate efficiently, cells must co-ordinate division with chromosome segregation. In Bacillus subtilis, the nucleoid occlusion protein Noc binds to specific DNA sequences (NBSs) scattered around the chromosome and helps to protect genomic integrity by coupling the initiation of division to the progression of chromosome replication and segregation. However, how it inhibits division has remained unclear. Here, we demonstrate that Noc associates with the cell membrane via an N-terminal amphipathic helix, which is necessary for function. Importantly, the membrane-binding affinity of this helix is weak and requires the assembly of nucleoprotein complexes, thus establishing a mechanism for DNA-dependent activation of Noc. Furthermore, division inhibition by Noc requires recruitment of NBS DNA to the cell membrane and is dependent on its ability to bind DNA and membrane simultaneously. Indeed, Noc production in a heterologous system is sufficient for recruitment of chromosomal DNA to the membrane. Our results suggest a simple model in which the formation of large membrane-associated nucleoprotein complexes physically occludes assembly of the division machinery.
为了高效增殖，细胞必须协调分裂与染色体分离。在枯草芽孢杆菌中，类核阻隔蛋白Noc与散布在染色体上的特定DNA序列（NBSs）结合，并通过将分裂起始与染色体复制和分离进程相耦合来帮助保护基因组完整性。然而，它如何抑制分裂仍不清楚。在这里，我们证明Noc通过一个N端两亲性螺旋与细胞膜结合，这对其功能是必需的。重要的是，这个螺旋的膜结合亲和力较弱，需要核蛋白复合物的组装，从而建立了一种Noc的DNA依赖性激活机制。此外，Noc对分裂的抑制需要将NBS DNA募集到细胞膜上，并且依赖于其同时结合DNA和膜的能力。实际上，在异源系统中产生Noc足以将染色体DNA募集到膜上。我们的结果提出了一个简单的模型，即大型膜相关核蛋白复合物的形成在物理上阻碍了分裂机器的组装。
