Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.
J Bacteriol. 2012 Sep;194(17):4608-18. doi: 10.1128/JB.00378-12. Epub 2012 Jun 22.
During sporulation, Bacillus subtilis redeploys the division protein FtsZ from midcell to the cell poles, ultimately generating an asymmetric septum. Here, we describe a sporulation-induced protein, RefZ, that facilitates the switch from a medial to a polar FtsZ ring placement. The artificial expression of RefZ during vegetative growth converts FtsZ rings into FtsZ spirals, arcs, and foci, leading to filamentation and lysis. Mutations in FtsZ specifically suppress RefZ-dependent division inhibition, suggesting that RefZ may target FtsZ. During sporulation, cells lacking RefZ are delayed in polar FtsZ ring formation, spending more time in the medial and transition stages of FtsZ ring assembly. A RefZ-green fluorescent protein (GFP) fusion localizes in weak polar foci at the onset of sporulation and as a brighter midcell focus at the time of polar division. RefZ has a TetR DNA binding motif, and point mutations in the putative recognition helix disrupt focus formation and abrogate cell division inhibition. Finally, chromatin immunoprecipitation assays identified sites of RefZ enrichment in the origin region and near the terminus. Collectively, these data support a model in which RefZ helps promote the switch from medial to polar division and is guided by the organization of the chromosome. Models in which RefZ acts as an activator of FtsZ ring assembly near the cell poles or as an inhibitor of the transient medial ring at midcell are discussed.
在芽孢形成过程中，枯草芽孢杆菌将分裂蛋白 FtsZ 从细胞中部重新分配到细胞两极，最终生成不对称的隔膜。在这里，我们描述了一种诱导型蛋白 RefZ，它有助于 FtsZ 环从中央位置向极部位置转移。在营养生长期间人工表达 RefZ 会将 FtsZ 环转化为 FtsZ 螺旋、弧和焦点，导致丝状化和裂解。FtsZ 突变特异性抑制 RefZ 依赖性的分裂抑制，这表明 RefZ 可能靶向 FtsZ。在芽孢形成过程中，缺乏 RefZ 的细胞在极部 FtsZ 环形成过程中延迟，在 FtsZ 环组装的中央和过渡阶段花费更多时间。RefZ-绿色荧光蛋白（GFP）融合蛋白在芽孢形成开始时在弱极焦点处定位，并在极部分裂时在中央强焦点处定位。RefZ 具有 TetR DNA 结合基序，在假定的识别螺旋中的点突变破坏焦点形成并消除细胞分裂抑制。最后，染色质免疫沉淀分析鉴定了 RefZ 在起始区和末端附近的富集位点。总的来说，这些数据支持了 RefZ 有助于促进从中央到极部分裂的转变的模型，并且该转变由染色体的组织决定。讨论了 RefZ 作为极部 FtsZ 环组装的激活剂或作为中央短暂的 FtsZ 环抑制剂的模型。
