Regional Control of Chromosome Segregation in Pseudomonas aeruginosa.
Regional Control of Chromosome Segregation in Pseudomonas aeruginosa.
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DOI：
10.1371/journal.pgen.1006428
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发表时间：
2016-11
期刊：
影响因子：
4.5
通讯作者：
Vallet-Gely I
中科院分区：
文献类型：
--
作者：
Lagage V;Boccard F;Vallet-Gely I
细菌中的染色体分离与DNA复制同时发生，含有复制起始位点的复制区域通常首先分离并迁移到细胞内的最终特定位置。在许多细菌物种中，称为ParABS系统的三组分分割机制对染色体分离至关重要。这就是铜绿假单胞菌中的情况，其中破坏ParABS系统对生长非常有害，因为它增加了生成时间并导致无核细胞的形成和细胞内oriC的错误定位。在本研究中，我们研究了铜绿假单胞菌体内的ParABS系统。利用染色质免疫沉淀结合高通量测序，我们发现ParB在体内结合了位于oriC 15kb内的四个parS位点，并且这种结合促进了高阶核蛋白复合物的形成。我们发现一个parS位点足以阻止无核细胞的形成，因此对于正确的染色体分离。通过将parS位点从其在染色体上的原始位置移开，我们证明parS是DNA复制时第一个分离的染色体位点，这表明它是分离过程中施加力的位点。我们在oriC周围发现了一个大约650 kb的区域，其中parS位点必须定位才能正确进行染色体分离，我们称之为parS位点的“能力区”。经过特定基因重排的突变株允许我们提出oriC和parS之间的距离定义了这个“能力区”。讨论了铜绿假单胞菌染色体分离控制的意义。遗传信息的准确传递依赖于复制和分离，这两个过程对所有生物体都是必不可少的。在细菌中，这些过程是同时发生的。细菌环状染色体的复制始于一个称为oriC的单一特定序列，并沿着染色体臂进行双向复制。在许多细菌中，一种叫做ParABS的分裂系统参与了染色体分离。它涉及ParB蛋白与parS序列的结合，parS序列通常在oriC附近发现。这一系统对染色体分离的重要性因物种而异，从必不可少到可有可无。在铜绿假单胞菌（Pseudomonas aeruginosa）这一重要的条件致病菌中，ParABS系统在染色体分离中起着重要作用，受该系统影响的突变体表现出严重的生长缺陷和无核细胞的形成，但不是必需的。在这项研究中，我们表征了P. aeruginosa中ParABS系统不同决定因素的活性，并证明parS位点位于oriC附近是至关重要的，这表明在复制后靠近oriC的区域分离的时间很重要，并且它可能是ParABS系统保持这种时间的功能。
Chromosome segregation in bacteria occurs concomitantly with DNA replication, and the duplicated regions containing the replication origin oriC are generally the first to separate and migrate to their final specific location inside the cell. In numerous bacterial species, a three-component partition machinery called the ParABS system is crucial for chromosome segregation. This is the case in the gammaproteobacterium Pseudomonas aeruginosa, where impairing the ParABS system is very detrimental for growth, as it increases the generation time and leads to the formation of anucleate cells and to oriC mispositioning inside the cell. In this study, we investigate in vivo the ParABS system in P. aeruginosa. Using chromatin immuno-precipitation coupled with high throughput sequencing, we show that ParB binds to four parS site located within 15 kb of oriC in vivo, and that this binding promotes the formation of a high order nucleoprotein complex. We show that one parS site is enough to prevent anucleate cell formation, therefore for correct chromosome segregation. By displacing the parS site from its native position on the chromosome, we demonstrate that parS is the first chromosomal locus to be separated upon DNA replication, which indicates that it is the site of force exertion of the segregation process. We identify a region of approximatively 650 kb surrounding oriC in which the parS site must be positioned for chromosome segregation to proceed correctly, and we called it “competence zone” of the parS site. Mutant strains that have undergone specific genetic rearrangements allow us to propose that the distance between oriC and parS defines this “competence zone”. Implications for the control of chromosome segregation in P. aeruginosa are discussed. Accurate transmission of the genetic information relies on replication and segregation, two processes essential to all living organisms. In bacteria, these processes occur concomitantly. Replication of the bacterial circular chromosome initiates at a single specific sequence called oriC, and proceed bi-directionally along the chromosome arms. A partition system called ParABS is involved in chromosome segregation in many bacteria. It involves the binding of the ParB protein to parS sequences, which are often found in the close vicinity of oriC. The importance of this system for chromosome segregation varies according to species, ranging from essential to dispensable. In Pseudomonas aeruginosa, an important opportunistic pathogen, the ParABS system plays an important role in chromosome segregation, as mutants affected in this system present a severe growth defect as well as anucleate cells formation, but is not essential. In this study, we characterize the activity of the different determinants of the ParABS system in P. aeruginosa and demonstrate that it is critical for the parS site to be located close to oriC, which suggest that the timing of separation of regions close to oriC after replication is important, and that it could be a function of the ParABS system to keep this timing.
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