The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Lucy Shapiro - One of the best experts on this subject based on the ideXlab platform.
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a spindle like apparatus guides Bacterial Chromosome segregation
Nature Cell Biology, 2010Co-Authors: Jerod L Ptacin, Esteban Toro, Steven F Lee, Ethan C Garner, Michael Eckart, Luis R Comolli, W E Moerner, Lucy ShapiroAbstract:In bacteria, Chromosomes are partitioned by the Par system. Super-resolution microscopy demonstrates that ParA and ParB forms a 'spindle-like' structure and suggests that the pole protein, TipN, anchors the DNA-bound ParA filaments at the new pole.
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Bacterial Chromosome organization and segregation
Cold Spring Harbor Perspectives in Biology, 2010Co-Authors: Esteban Toro, Lucy ShapiroAbstract:Bacterial Chromosomes are generally approximately 1000 times longer than the cells in which they reside, and concurrent replication, segregation, and transcription/translation of this crowded mass of DNA poses a challenging organizational problem. Recent advances in cell-imaging technology with subdiffraction resolution have revealed that the Bacterial nucleoid is reliably oriented and highly organized within the cell. Such organization is transmitted from one generation to the next by progressive segregation of daughter Chromosomes and anchoring of DNA to the cell envelope. Active segregation by a mitotic machinery appears to be common; however, the mode of Chromosome segregation varies significantly from species to species.
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Bacterial Chromosome Organization and Segregation
Cold Spring Harbor perspectives in biology, 2010Co-Authors: Esteban Toro, Lucy ShapiroAbstract:The DNA molecule is a remarkably simple and elegant storage medium for genetic information. However, linear encoding of this kind demands an inordinately long molecule, and so, Bacterial Chromosomes are much longer than the cells in which they reside. For example, Caulobacter crescentus packages a 1.3 mm (4.0 Mbp) genome in a 2 micron cell. This spatial constraint creates a daunting organizational problem that is exacerbated on DNA replication, an act that not only doubles the amount of DNA in the cell, but also creates topologically linked molecules. Watson and Crick published a companion paper to their 1953 DNA structure in which they pointed out that the elegant simplicity of the copying mechanism they proposed was complicated by the fact that the two strands wind around each other. Hence, to create two separate Chromosomes, it is necessary to unlink the original two strands, which, even in the case of a Bacterial genome, amounts to unwinding several hundreds of thousands of turns. They wrote: “Although it is difficult at the moment to see how these processes occur without everything getting tangled, we do not feel that this objection will be insuperable” (Watson and Crick 1953). Indeed, in 1971, James Wang purified the first of a class of proteins we now know as DNA topoisomerases (Wang 1971), which solve this particular problem by catalyzing the passage of single strands or duplexes of DNA through each other (Schoeffler and Berger 2008). Topoisomerases thus provide a solution to the problem of DNA tangling within the cell. Other, less biochemically tractable aspects of DNA spatial organization, however, received little attention for a considerable time, partly for technical reasons, but also because bacteria were seen as the proverbial “bag of enzymes,” i.e., small enough for diffusive processes to dominate and thus not requiring any spatial organization. We now know that the Bacterial cell is in fact highly organized (Thanbichler and Shapiro 2008), and the Chromosome is no exception. Here, we concentrate on recent findings about the dynamic high-order organization of the Bacterial Chromosome; that is, how is DNA organized within the cell and how is it segregated faithfully to each daughter cell on division? Our understanding of these two questions has progressed greatly in the past few years, aided in large part by advances in imaging technologies. For the sake of clarity, we explore each question independently. However, as will be clear throughout, DNA segregation and organization are intimately linked.
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MreB Actin-Mediated Segregation of a Specific Region of a Bacterial Chromosome
Cell, 2005Co-Authors: Zemer Gitai, Natalie A. Dye, Ann Reisenauer, Masaaki Wachi, Lucy ShapiroAbstract:Faithful Chromosome segregation is an essential component of cell division in all organisms. The eukaryotic mitotic machinery uses the cytoskeleton to move specific chromosomal regions. To investigate the potential role of the actin-like MreB protein in Bacterial Chromosome segregation, we first demonstrate that MreB is the direct target of the small molecule A22. We then demonstrate that A22 completely blocks the movement of newly replicated loci near the origin of replication but has no qualitative or quantitative effect on the segregation of other loci if added after origin segregation. MreB selectively interacts, directly or indirectly, with origin-proximal regions of the Chromosome, arguing that the origin-proximal region segregates via an MreB-dependent mechanism not used by the rest of the Chromosome.
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The structure and function of the Bacterial Chromosome.
Current opinion in genetics & development, 2005Co-Authors: Martin Thanbichler, Patrick H. Viollier, Lucy ShapiroAbstract:Advances in microscopic and cell biological techniques have considerably improved our understanding of Bacterial Chromosome organization and dynamics. The nucleoid was formerly perceived to be an amorphous entity divided into ill-defined domains of supercoiling that are randomly deposited in the cell. Recent work, however, has demonstrated a remarkable degree of spatial organization. A highly ordered Chromosome structure, established while DNA replication and partitioning are in progress, is maintained and propagated during growth. Duplication of the Chromosome and partitioning of the newly generated daughter strands are interwoven processes driven by the dynamic interplay between the synthesis, segregation and condensation of DNA. These events are intimately coupled with the Bacterial cell cycle and exhibit a previously unanticipated complexity reminiscent of eukaryotic systems.
David J. Sherratt - One of the best experts on this subject based on the ideXlab platform.
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SMC complexes organize the Bacterial Chromosome by lengthwise compaction.
Current genetics, 2020Co-Authors: Jarno Mäkelä, David J. SherrattAbstract:Structural maintenance of Chromosomes (SMC) complexes are ancient and conserved molecular machines that organize Chromosomes in all domains of life. We propose that the principles of Chromosome folding needed to accommodate DNA inside a cell in an accessible form will follow similar principles in prokaryotes and eukaryotes. However, the exact contributions of SMC complexes to Bacterial Chromosome organization have been elusive. Recently, it was shown that the SMC homolog, MukBEF, organizes and individualizes the Escherichia coli Chromosome by forming a filamentous axial core from which DNA loops emanate, similar to the action of condensin in mitotic Chromosome formation. MukBEF action, along with its interaction with the partner protein, MatP, also facilitates Chromosome individualization by directing opposite Chromosome arms (replichores) to different cell halves. This contrasts with the situation in many other bacteria, where SMC complexes organise Chromosomes in a way that the opposite replichores are aligned along the long axis of the cell. We highlight the similarities and differences of SMC complex contributions to Chromosome organization in bacteria and eukaryotes, and summarize the current mechanistic understanding of the processes.
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the Bacterial Chromosome architecture and action of Bacterial smc and smc like complexes
Fems Microbiology Reviews, 2014Co-Authors: Sophie Nolivos, David J. SherrattAbstract:Structural Maintenance of Chromosomes (SMC) protein complexes are found in all three domains of life. They are characterized by a distinctive and conserved architecture in which a globular ATPase ‘head’ domain is formed by the N- and C-terminal regions of the SMC protein coming together, with a c. 50-nm-long antiparallel coiled-coil separating the head from a dimerization ‘hinge’. Dimerization gives both V- and O-shaped SMC dimers. The distinctive architecture points to a conserved biochemical mechanism of action. However, the details of this mechanism are incomplete, and the precise ways in which this mechanism leads to the biological functions of these complexes in Chromosome organization and processing remain unclear. In this review, we introduce the properties of Bacterial SMC complexes, compare them with eukaryotic complexes and discuss how their likely biochemical action relates to their roles in Chromosome organization and segregation.
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Bacterial Chromosome Dynamics
Science (New York N.Y.), 2003Co-Authors: David J. SherrattAbstract:Bacterial Chromosomes are highly compacted structures and share many properties with their eukaryote counterparts, despite not being organized into chromatin or being contained within a cell nucleus. Proteins conserved across all branches of life act in Chromosome organization, and common mechanisms maintain genome integrity and ensure faithful replication. The principles that underlie Chromosome segregation in bacteria and eukaryotes share similarities, although bacteria segregate DNA as it replicates and lack a eukaryote-like mitotic apparatus for segregating Chromosomes. This may be because the distances that newly replicated Bacterial Chromosomes move apart before cell division are small as compared to those in eukaryotes. Bacteria specify positional information, which determines where cell division will occur and which places the replication machinery and chromosomal loci at defined locations that change during cell cycle progression.
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Divide and rule: the Bacterial Chromosome
Trends in genetics : TIG, 2001Co-Authors: David J. SherrattAbstract:Abstract The Keystone Symposium on Bacterial Chromosomes was held in Santa Fe, NM, USA, from 7–13 February, 2001.
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ftsk functions in the processing of a holliday junction intermediate during Bacterial Chromosome segregation
Genes & Development, 2000Co-Authors: Francoisxavier Barre, Mira Aroyo, Sean D Colloms, Annett Helfrich, Francois Cornet, David J. SherrattAbstract:In bacteria with circular Chromosomes, homologous recombination can generate Chromosome dimers that cannot be segregated to daughter cells at cell division. Xer site-specific recombination at dif, a 28-bp site located in the replication terminus region of the Chromosome, converts dimers to monomers through the sequential action of the XerC and XerD recombinases. Chromosome dimer resolution requires that dif is positioned correctly in the Chromosome, and the activity of FtsK, a septum-located protein that coordinates cell division with Chromosome segregation. Here, we show that cycles of XerC-mediated strand exchanges form and resolve Holliday junction intermediates back to substrate irrespective of whether conditions support a complete recombination reaction. The C-terminal domain of FtsK is sufficient to activate the exchange of the second pair of strands by XerD, allowing both intra- and intermolecular recombination reactions to go to completion. Proper positioning of dif in the Chromosome and of FtsK at the septum is required to sense the multimeric state of newly replicated Chromosomes and restrict complete Xer reactions to dimeric Chromosomes.
John F. Marko - One of the best experts on this subject based on the ideXlab platform.
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Facilitated Dissociation of a Nucleoid Protein from the Bacterial Chromosome.
Journal of bacteriology, 2016Co-Authors: Nastaran Hadizadeh, Reid C. Johnson, John F. MarkoAbstract:UNLABELLED Off-rates of proteins from the DNA double helix are widely considered to be dependent only on the interactions inside the initially bound protein-DNA complex and not on the concentration of nearby molecules. However, a number of recent single-DNA experiments have shown off-rates that depend on solution protein concentration, or "facilitated dissociation." Here, we demonstrate that this effect occurs for the major Escherichia coli nucleoid protein Fis on isolated Bacterial Chromosomes. We isolated E. coli nucleoids and showed that dissociation of green fluorescent protein (GFP)-Fis is controlled by solution Fis concentration and exhibits an "exchange" rate constant (kexch) of ≈10(4) M(-1) s(-1), comparable to the rate observed in single-DNA experiments. We also show that this effect is strongly salt dependent. Our results establish that facilitated dissociation can be observed in vitro on Chromosomes assembled in vivo IMPORTANCE Bacteria are important model systems for the study of gene regulation and Chromosome dynamics, both of which fundamentally depend on the kinetics of binding and unbinding of proteins to DNA. In experiments on isolated E. coli Chromosomes, this study showed that the prolific transcription factor and Chromosome packaging protein Fis displays a strong dependence of its off-rate from the Bacterial Chromosome on Fis concentration, similar to that observed in in vitro experiments. Therefore, the free cellular DNA-binding protein concentration can strongly affect lifetimes of proteins bound to the Chromosome and must be taken into account in quantitative considerations of gene regulation. These results have particularly profound implications for transcription factors where DNA binding lifetimes can be a critical determinant of regulatory function.
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Structure and Mechanical Properties of the Bacterial Chromosome in E.Coli
Biophysical Journal, 2014Co-Authors: Nastaran Hadizadeh, Calin C. Guet, Reid C. Johnson, John F. MarkoAbstract:Our knowledge of the scheme by which the Bacterial Chromosome is physically organized is at best incomplete. Through in vivo visualization using an inducible GFP fusion to the nucleoid-associated protein Fis, to non-specifically decorate the entire Chromosome, we have been able to observe the global Chromosome structure in live cells, where the dynamics of structure could be followed in real time. Quantitative analyses of the nucleoid and subnucleoid structures have indicated that the Chromosome is a self-adherent, folded object with defined and long-lived folding patterns, including an overall coiled shape, in which nucleoid-associated proteins play a major role. In addition to the in vivo studies, we have developed an assay to carry out mechanical experiments on nucleoids removed from cells, using magnetic tweezers technique. We use this assay to study the effects of the major nucleoid-associated proteins mutations on the Chromosome by probing changes in the mechanical properties, in order to get a better understanding of the roles played by major Chromosome-folding proteins in organizing the physical state of the Chromosome.
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Structure and Dynamics of the Bacterial Chromosome in E. coli
Biophysical Journal, 2011Co-Authors: Nastaran Hadizadeh, Calin C. Guet, Reid C. Johnson, John F. MarkoAbstract:The Bacterial cell's ability to control the topology of a long DNA in the confined environment of the cell is quite remarkable. Despite a great number of studies on bacteria, and especially E coli, our understanding of the spatio-temporal organization of Bacterial Chromosomes is minimal, partly because their dynamics have been difficult to observe directly. To visualize Bacterial Chromosome conformation within living cells, we have developed a Bacterial strain containing fluorescent gfp-fusion versions of a Chromosome folding protein, Fis, under inducible control. Bacterial Chromosomes have been studied in cells and removed from cells, in order to establish their spatial organization and mechanical properties, and to study how those properties are changed by varied external conditions. Space-time studies of the nucleoid in live E coli cells shows a relation between Chromosome segregation and cell division under different growth conditions, and it also shows how domain structure and overall conformation of Chromosomes vary during rapid and slow growth. In order to study the Bacterial Chromosome outside of the cell, we have developed methods for isolation of single Bacterial Chromosomes and directly examining nucleoid mechanical properties as a function of protein levels using micromanipulation methods.
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Structure and Dynamics of the Bacterial Chromosome in E. Coli Monitored by Gfp-Fis
Biophysical Journal, 2010Co-Authors: Nastaran Hadizadeh, John F. MarkoAbstract:The Bacterial cell's ability to control the topology of the 1.5 mm-long DNA in the confined environment of the cell is quite remarkable. Despite a great number of studies on bacteria, and especially E coli, our understanding of the spatio-temporal organization of Bacterial Chromosomes is minimal, partly because their dynamics have been difficult to observe directly. Using fluorescent-protein techniques we can visualize Bacterial Chromosome conformation during cell growth and division through fluorescent microscopy. We have developed a Bacterial strain containing fluorescent gfp-fusion versions of a Chromosome folding protein, Fis, under inducible control. Bacterial Chromosomes have been studied in cells and removed from cells, in order to establish their spatial organization and mechanical properties, and to study how those properties are changed by varied external conditions. Space-time studies of the nucleoid in live E coli cells shows how domain structure and overall conformation of Chromosomes vary during rapid and slow growth, and it also shows a relation between Chromosome segregation and cell division under these different growth conditions. In order to study the Bacterial Chromosome outside of the cell, we have developed methods for isolation of single Bacterial Chromosomes and our further objective will be to directly examine nucleoid mechanical properties as a function of protein levels using micromanipulation methods.
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Structure and Dynamics of the Bacterial Chromosome
Biophysical Journal, 2009Co-Authors: Nastaran Hadizadeh, John F. MarkoAbstract:Despite the great deal of studies on bacteria, and especially E coli, our understanding of the spatio-temporal organization of Bacterial Chromosomes is minimal, largely because their dynamics have been difficult to observe directly. Even more remarkable is bacteria's ability to control the topology of the 1.5 mm-long DNA in the confined environment of the cell. The objective of our project is to study dynamics of Chromosome structure during the process of cell division at the single-cell level, in the bacterium E. coli. Using a unique microcolony growth technique, we track cell growth and with fluorescent-protein techniques we can monitor Chromosome folding and quantify gene expression levels through fluorescence microscopy. We have developed a Bacterial strain containing fluorescent gfp-fusion versions of a Chromosome-folding protein, Fis, under inducible control. This strain is used to visualize Bacterial Chromosome conformation during cell growth and division. Our further objective will be quantitatively analyze the coupling of nucleoid protein level and Chromosome folding to gene expression, and to directly examine nucleoid mechanical properties as a function of protein levels using micromanipulation methods.
Nastaran Hadizadeh - One of the best experts on this subject based on the ideXlab platform.
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Facilitated Dissociation of a Nucleoid Protein from the Bacterial Chromosome.
Journal of bacteriology, 2016Co-Authors: Nastaran Hadizadeh, Reid C. Johnson, John F. MarkoAbstract:UNLABELLED Off-rates of proteins from the DNA double helix are widely considered to be dependent only on the interactions inside the initially bound protein-DNA complex and not on the concentration of nearby molecules. However, a number of recent single-DNA experiments have shown off-rates that depend on solution protein concentration, or "facilitated dissociation." Here, we demonstrate that this effect occurs for the major Escherichia coli nucleoid protein Fis on isolated Bacterial Chromosomes. We isolated E. coli nucleoids and showed that dissociation of green fluorescent protein (GFP)-Fis is controlled by solution Fis concentration and exhibits an "exchange" rate constant (kexch) of ≈10(4) M(-1) s(-1), comparable to the rate observed in single-DNA experiments. We also show that this effect is strongly salt dependent. Our results establish that facilitated dissociation can be observed in vitro on Chromosomes assembled in vivo IMPORTANCE Bacteria are important model systems for the study of gene regulation and Chromosome dynamics, both of which fundamentally depend on the kinetics of binding and unbinding of proteins to DNA. In experiments on isolated E. coli Chromosomes, this study showed that the prolific transcription factor and Chromosome packaging protein Fis displays a strong dependence of its off-rate from the Bacterial Chromosome on Fis concentration, similar to that observed in in vitro experiments. Therefore, the free cellular DNA-binding protein concentration can strongly affect lifetimes of proteins bound to the Chromosome and must be taken into account in quantitative considerations of gene regulation. These results have particularly profound implications for transcription factors where DNA binding lifetimes can be a critical determinant of regulatory function.
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Structure and Mechanical Properties of the Bacterial Chromosome in E.Coli
Biophysical Journal, 2014Co-Authors: Nastaran Hadizadeh, Calin C. Guet, Reid C. Johnson, John F. MarkoAbstract:Our knowledge of the scheme by which the Bacterial Chromosome is physically organized is at best incomplete. Through in vivo visualization using an inducible GFP fusion to the nucleoid-associated protein Fis, to non-specifically decorate the entire Chromosome, we have been able to observe the global Chromosome structure in live cells, where the dynamics of structure could be followed in real time. Quantitative analyses of the nucleoid and subnucleoid structures have indicated that the Chromosome is a self-adherent, folded object with defined and long-lived folding patterns, including an overall coiled shape, in which nucleoid-associated proteins play a major role. In addition to the in vivo studies, we have developed an assay to carry out mechanical experiments on nucleoids removed from cells, using magnetic tweezers technique. We use this assay to study the effects of the major nucleoid-associated proteins mutations on the Chromosome by probing changes in the mechanical properties, in order to get a better understanding of the roles played by major Chromosome-folding proteins in organizing the physical state of the Chromosome.
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Structure and Dynamics of the Bacterial Chromosome in E. coli
Biophysical Journal, 2011Co-Authors: Nastaran Hadizadeh, Calin C. Guet, Reid C. Johnson, John F. MarkoAbstract:The Bacterial cell's ability to control the topology of a long DNA in the confined environment of the cell is quite remarkable. Despite a great number of studies on bacteria, and especially E coli, our understanding of the spatio-temporal organization of Bacterial Chromosomes is minimal, partly because their dynamics have been difficult to observe directly. To visualize Bacterial Chromosome conformation within living cells, we have developed a Bacterial strain containing fluorescent gfp-fusion versions of a Chromosome folding protein, Fis, under inducible control. Bacterial Chromosomes have been studied in cells and removed from cells, in order to establish their spatial organization and mechanical properties, and to study how those properties are changed by varied external conditions. Space-time studies of the nucleoid in live E coli cells shows a relation between Chromosome segregation and cell division under different growth conditions, and it also shows how domain structure and overall conformation of Chromosomes vary during rapid and slow growth. In order to study the Bacterial Chromosome outside of the cell, we have developed methods for isolation of single Bacterial Chromosomes and directly examining nucleoid mechanical properties as a function of protein levels using micromanipulation methods.
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Structure and Dynamics of the Bacterial Chromosome in E. Coli Monitored by Gfp-Fis
Biophysical Journal, 2010Co-Authors: Nastaran Hadizadeh, John F. MarkoAbstract:The Bacterial cell's ability to control the topology of the 1.5 mm-long DNA in the confined environment of the cell is quite remarkable. Despite a great number of studies on bacteria, and especially E coli, our understanding of the spatio-temporal organization of Bacterial Chromosomes is minimal, partly because their dynamics have been difficult to observe directly. Using fluorescent-protein techniques we can visualize Bacterial Chromosome conformation during cell growth and division through fluorescent microscopy. We have developed a Bacterial strain containing fluorescent gfp-fusion versions of a Chromosome folding protein, Fis, under inducible control. Bacterial Chromosomes have been studied in cells and removed from cells, in order to establish their spatial organization and mechanical properties, and to study how those properties are changed by varied external conditions. Space-time studies of the nucleoid in live E coli cells shows how domain structure and overall conformation of Chromosomes vary during rapid and slow growth, and it also shows a relation between Chromosome segregation and cell division under these different growth conditions. In order to study the Bacterial Chromosome outside of the cell, we have developed methods for isolation of single Bacterial Chromosomes and our further objective will be to directly examine nucleoid mechanical properties as a function of protein levels using micromanipulation methods.
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Structure and Dynamics of the Bacterial Chromosome
Biophysical Journal, 2009Co-Authors: Nastaran Hadizadeh, John F. MarkoAbstract:Despite the great deal of studies on bacteria, and especially E coli, our understanding of the spatio-temporal organization of Bacterial Chromosomes is minimal, largely because their dynamics have been difficult to observe directly. Even more remarkable is bacteria's ability to control the topology of the 1.5 mm-long DNA in the confined environment of the cell. The objective of our project is to study dynamics of Chromosome structure during the process of cell division at the single-cell level, in the bacterium E. coli. Using a unique microcolony growth technique, we track cell growth and with fluorescent-protein techniques we can monitor Chromosome folding and quantify gene expression levels through fluorescence microscopy. We have developed a Bacterial strain containing fluorescent gfp-fusion versions of a Chromosome-folding protein, Fis, under inducible control. This strain is used to visualize Bacterial Chromosome conformation during cell growth and division. Our further objective will be quantitatively analyze the coupling of nucleoid protein level and Chromosome folding to gene expression, and to directly examine nucleoid mechanical properties as a function of protein levels using micromanipulation methods.
Esteban Toro - One of the best experts on this subject based on the ideXlab platform.
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a spindle like apparatus guides Bacterial Chromosome segregation
Nature Cell Biology, 2010Co-Authors: Jerod L Ptacin, Esteban Toro, Steven F Lee, Ethan C Garner, Michael Eckart, Luis R Comolli, W E Moerner, Lucy ShapiroAbstract:In bacteria, Chromosomes are partitioned by the Par system. Super-resolution microscopy demonstrates that ParA and ParB forms a 'spindle-like' structure and suggests that the pole protein, TipN, anchors the DNA-bound ParA filaments at the new pole.
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Bacterial Chromosome organization and segregation
Cold Spring Harbor Perspectives in Biology, 2010Co-Authors: Esteban Toro, Lucy ShapiroAbstract:Bacterial Chromosomes are generally approximately 1000 times longer than the cells in which they reside, and concurrent replication, segregation, and transcription/translation of this crowded mass of DNA poses a challenging organizational problem. Recent advances in cell-imaging technology with subdiffraction resolution have revealed that the Bacterial nucleoid is reliably oriented and highly organized within the cell. Such organization is transmitted from one generation to the next by progressive segregation of daughter Chromosomes and anchoring of DNA to the cell envelope. Active segregation by a mitotic machinery appears to be common; however, the mode of Chromosome segregation varies significantly from species to species.
-
Bacterial Chromosome Organization and Segregation
Cold Spring Harbor perspectives in biology, 2010Co-Authors: Esteban Toro, Lucy ShapiroAbstract:The DNA molecule is a remarkably simple and elegant storage medium for genetic information. However, linear encoding of this kind demands an inordinately long molecule, and so, Bacterial Chromosomes are much longer than the cells in which they reside. For example, Caulobacter crescentus packages a 1.3 mm (4.0 Mbp) genome in a 2 micron cell. This spatial constraint creates a daunting organizational problem that is exacerbated on DNA replication, an act that not only doubles the amount of DNA in the cell, but also creates topologically linked molecules. Watson and Crick published a companion paper to their 1953 DNA structure in which they pointed out that the elegant simplicity of the copying mechanism they proposed was complicated by the fact that the two strands wind around each other. Hence, to create two separate Chromosomes, it is necessary to unlink the original two strands, which, even in the case of a Bacterial genome, amounts to unwinding several hundreds of thousands of turns. They wrote: “Although it is difficult at the moment to see how these processes occur without everything getting tangled, we do not feel that this objection will be insuperable” (Watson and Crick 1953). Indeed, in 1971, James Wang purified the first of a class of proteins we now know as DNA topoisomerases (Wang 1971), which solve this particular problem by catalyzing the passage of single strands or duplexes of DNA through each other (Schoeffler and Berger 2008). Topoisomerases thus provide a solution to the problem of DNA tangling within the cell. Other, less biochemically tractable aspects of DNA spatial organization, however, received little attention for a considerable time, partly for technical reasons, but also because bacteria were seen as the proverbial “bag of enzymes,” i.e., small enough for diffusive processes to dominate and thus not requiring any spatial organization. We now know that the Bacterial cell is in fact highly organized (Thanbichler and Shapiro 2008), and the Chromosome is no exception. Here, we concentrate on recent findings about the dynamic high-order organization of the Bacterial Chromosome; that is, how is DNA organized within the cell and how is it segregated faithfully to each daughter cell on division? Our understanding of these two questions has progressed greatly in the past few years, aided in large part by advances in imaging technologies. For the sake of clarity, we explore each question independently. However, as will be clear throughout, DNA segregation and organization are intimately linked.