Mechanisms of Chromosome Maintenance in Bacteria

细菌染色体维持机制

基本信息

项目摘要

A recent development in the field of E. coli DNA replication is the identification of weak (incognito) binding sites for the initiator DnaA in the origin of replication, called I-sites. These sites play a key role in timing of replication initiation in the cell cycle. Because of the difficulty of recognizing I-sites, the generality of their occurrence has remained obscure. Richard Fekete and Tatiana Venkova-Canova have succeeded in localizing sequences with characteristics of an I-site in a second system (in the replication origin of plasmid P1). The sequence information should help to define an I-site better and thus help identification of such sites in other systems and study their roles in replication control. Bacteria capable of rapid proliferation such as E. coli and B. subtilis usually amplify the origin proximal region of their chromosome. In V. cholerae, Preeti Srivastava found this to be true for chromosome I but not II. The growth-rate insensitive behavior of the latter turned out to be due to homeostatic controls on its initiator RctB. Relaxing the control increased the copy number of chromosome II but decreased the cell growth rate, suggesting that this chromosome might serve as a repository for potentially deleterious genes. These genes thus could play a role in maintaining relative copy number of the two chromosomes. Ryosuke Kadoya is standardizing conditions to selectively inhibit replication initiation of one of the two Vibrio chromosomes and study the consequences to replication and segregation of the other chromosome, as well as to cell growth and division. These studies are expected to provide initial evidence for communication between the two chromosomes and whether mechanisms exist in bacteria analogous to check-point controls prevalent in eukaryotes. To study the regulation of replication of chromosome II, Tatiana Venkova-Canova has defined the bounds of the replication origin and adjoining sequences that serve to control replication initiation negatively. The origin resembles those of some plasmids but the negative control locus is more extended and complex compared to the plasmids. A novel mechanism was found that controls the level of chromosome II specific initiator, RctB, homeostatically, and thereby the replication initiation frequency. Unlike in E. coli, where DNA adenine methylase (Dam) plays a facilitatory role in DNA replication, the enzyme appears essential for replication of both the chromosomes of V. cholerae. The exact role of Dam in replication is not known but most likely it alters the structure of origin DNA that eases its melting, a crucial step in replication initiation. Dam can also modulate gene expression by methylating promoter DNA, and could play an indirect role by supplying a gene product crucial for replication initiation. Gaelle Demarre is testing these alternate possibilities on how Dam could be playing its obligatory role in V. cholerae. The equivalent of microtubules of the eukaryotic mitotic apparatus has not been found in bacteria, and how the bacterial chromosomes segregate has remained largely enigmatic. The recent discovery in bacteria of an actin homolog, MreB, is of special interest because of its suggested role in chromosome segregation. Preeti Srivastava found that the properties of V. cholerae MreB to be similar to its homolog in other bacteria, and that alteration of the protein led to gross distortion in nucleoid morphology and localization of centromeric regions for both the chromosomes. In V. cholerae, Ranajit Ghosh has identified the centromere for chromosome I. A couple of centromere-associated proteins (ParA and ParB) have been purified. To understand how the centromere is utilized to segregate and retain the sister chromosomes in opposite cell halves, Ranajit Ghosh is trying to identify proteins that may serve as mitotic motors or chromosomal anchors. He has been able to co-immuno-precipitate several proteins from crude cell extracts using antibodies against ParAB proteins. The proteins are being identified using LCMS/MS.
大肠杆菌DNA复制领域的最新进展是鉴定复制起源中启动DNA的弱(不可见)结合位点,称为i位点。这些位点在细胞周期的复制起始时间中起关键作用。由于难以识别i位点,它们发生的普遍性仍然模糊不清。Richard Fekete和Tatiana Venkova-Canova成功地在第二个系统(质粒P1的复制起源)中定位了具有i位点特征的序列。序列信息应该有助于更好地定义i位点,从而有助于识别其他系统中的此类位点,并研究它们在复制控制中的作用。大肠杆菌和枯草芽孢杆菌等能够快速增殖的细菌通常会扩增其染色体的近端起源区域。在霍乱弧菌中,Preeti Srivastava发现这对1号染色体是正确的,而对2号染色体则不是。后者的生长速率不敏感行为被证明是由于对其引发剂RctB的稳态控制。放松控制增加了II号染色体的拷贝数,但降低了细胞的生长速度,表明这条染色体可能是潜在有害基因的储存库。因此,这些基因可能在维持两条染色体的相对拷贝数方面发挥作用。Ryosuke Kadoya正在标准化条件,选择性地抑制两条弧菌染色体之一的复制起始,并研究对另一条染色体的复制和分离以及细胞生长和分裂的影响。这些研究有望为两条染色体之间的交流以及细菌中是否存在类似于真核生物中普遍存在的检查点控制机制提供初步证据。为了研究II号染色体的复制调控,Tatiana Venkova-Canova定义了复制起源和相邻序列的界限,这些序列对复制起始起负调控作用。其起源与一些质粒相似,但阴性控制位点比质粒更广泛和复杂。研究发现了一种新的机制,可以动态控制染色体II特异性启动物RctB的水平,从而控制复制起始频率。与大肠杆菌中DNA腺嘌呤甲基化酶(Dam)在DNA复制中起促进作用不同,该酶似乎对霍乱弧菌两条染色体的复制都至关重要。Dam在复制中的确切作用尚不清楚,但最有可能的是它改变了起源DNA的结构,从而减缓了它的融化,这是复制开始的关键步骤。Dam还可以通过甲基化启动子DNA来调节基因表达,并可能通过提供对复制起始至关重要的基因产物来发挥间接作用。Gaelle Demarre正在测试Dam如何在霍乱弧菌中发挥其必要作用的这些可能性。在细菌中还没有发现真核生物有丝分裂装置的等效微管,细菌染色体如何分离在很大程度上仍然是一个谜。最近在细菌中发现了一种肌动蛋白同源物MreB,由于其在染色体分离中的作用而引起了特别的兴趣。Preeti Srivastava发现霍乱弧菌MreB的特性与其在其他细菌中的同源物相似,并且该蛋白的改变导致两条染色体的类核形态和着丝粒区域定位的严重扭曲。在霍乱弧菌中,Ranajit Ghosh已经鉴定出i号染色体的着丝粒,并纯化了一对着丝粒相关蛋白(ParA和ParB)。为了了解着丝粒是如何被用来分离和保留相对细胞一半的姐妹染色体的,Ranajit Ghosh正试图识别可能作为有丝分裂发动机或染色体锚点的蛋白质。他已经能够使用针对ParAB蛋白的抗体从粗细胞提取物中共免疫沉淀几种蛋白质。利用LCMS/MS对蛋白进行鉴定。

项目成果

期刊论文数量(7)
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DHRUBA K CHATTORAJ其他文献

DHRUBA K CHATTORAJ的其他文献

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{{ truncateString('DHRUBA K CHATTORAJ', 18)}}的其他基金

Mechanisms of Chromosome Maintenance in Bacteria
细菌染色体维持机制
  • 批准号:
    7965220
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:
Mechanisms of Chromosome Maintenance in Bacteria
细菌染色体维持机制
  • 批准号:
    8937695
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:
Mechanisms of Chromosome Maintenance in Bacteria
细菌染色体维持机制
  • 批准号:
    10262055
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:
Mechanisms of Chromosome Maintenance in Bacteria
细菌染色体维持机制
  • 批准号:
    8763060
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:
CONTROL OF DNA REPLICATION
DNA 复制的控制
  • 批准号:
    6289345
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:
Mechanisms of Chromosome Maintenance in Bacteria
细菌染色体维持机制
  • 批准号:
    9153531
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:
Mechanisms of Chromosome Maintenance in Bacteria
细菌染色体维持机制
  • 批准号:
    7592644
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:
Mechanisms of Chromosome Maintenance in Bacteria
细菌染色体维持机制
  • 批准号:
    7338296
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:
Mechanisms of Chromosome Maintenance in Bacteria
细菌染色体维持机制
  • 批准号:
    8552651
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:
Mechanisms of Chromosome Maintenance in Bacteria
细菌染色体维持机制
  • 批准号:
    6950973
  • 财政年份:
  • 资助金额:
    $ 98.51万
  • 项目类别:

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