1
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Puentes-Rodriguez SG, Norcross J, Mera PE. To let go or not to let go: how ParA can impact the release of the chromosomal anchoring in Caulobacter crescentus. Nucleic Acids Res 2023; 51:12275-12287. [PMID: 37933842 PMCID: PMC10711552 DOI: 10.1093/nar/gkad982] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Revised: 10/06/2023] [Accepted: 10/17/2023] [Indexed: 11/08/2023] Open
Abstract
Chromosomal maintenance is vital for the survival of bacteria. In Caulobacter crescentus, chromosome replication initiates at ori and segregation is delayed until the nearby centromere-like region parS is replicated. Our understanding of how this sequence of events is regulated remains limited. The segregation of parS has been shown to involve multiple steps including polar release from anchoring protein PopZ, slow movement and fast ParA-dependent movement to the opposite cell pole. In this study, we demonstrate that ParA's competing attractions from PopZ and from DNA are critical for segregation of parS. Interfering with this balance of attractions-by expressing a variant ParA-R195E unable to bind DNA and thus favoring interactions exclusively between ParA-PopZ-results in cell death. Our data revealed that ParA-R195E's sole interactions with PopZ obstruct PopZ's ability to release the polar anchoring of parS, resulting in cells with multiple parS loci fixed at one cell pole. We show that the inability to separate and segregate multiple parS loci from the pole is specifically dependent on the interaction between ParA and PopZ. Collectively, our results reveal that the initial steps in chromosome segregation are highly regulated.
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Affiliation(s)
| | - John D Norcross
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Paola E Mera
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
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2
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Junier I, Ghobadpour E, Espeli O, Everaers R. DNA supercoiling in bacteria: state of play and challenges from a viewpoint of physics based modeling. Front Microbiol 2023; 14:1192831. [PMID: 37965550 PMCID: PMC10642903 DOI: 10.3389/fmicb.2023.1192831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 09/25/2023] [Indexed: 11/16/2023] Open
Abstract
DNA supercoiling is central to many fundamental processes of living organisms. Its average level along the chromosome and over time reflects the dynamic equilibrium of opposite activities of topoisomerases, which are required to relax mechanical stresses that are inevitably produced during DNA replication and gene transcription. Supercoiling affects all scales of the spatio-temporal organization of bacterial DNA, from the base pair to the large scale chromosome conformation. Highlighted in vitro and in vivo in the 1960s and 1970s, respectively, the first physical models were proposed concomitantly in order to predict the deformation properties of the double helix. About fifteen years later, polymer physics models demonstrated on larger scales the plectonemic nature and the tree-like organization of supercoiled DNA. Since then, many works have tried to establish a better understanding of the multiple structuring and physiological properties of bacterial DNA in thermodynamic equilibrium and far from equilibrium. The purpose of this essay is to address upcoming challenges by thoroughly exploring the relevance, predictive capacity, and limitations of current physical models, with a specific focus on structural properties beyond the scale of the double helix. We discuss more particularly the problem of DNA conformations, the interplay between DNA supercoiling with gene transcription and DNA replication, its role on nucleoid formation and, finally, the problem of scaling up models. Our primary objective is to foster increased collaboration between physicists and biologists. To achieve this, we have reduced the respective jargon to a minimum and we provide some explanatory background material for the two communities.
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Affiliation(s)
- Ivan Junier
- CNRS, UMR 5525, VetAgro Sup, Grenoble INP, TIMC, Université Grenoble Alpes, Grenoble, France
| | - Elham Ghobadpour
- CNRS, UMR 5525, VetAgro Sup, Grenoble INP, TIMC, Université Grenoble Alpes, Grenoble, France
- École Normale Supérieure (ENS) de Lyon, CNRS, Laboratoire de Physique and Centre Blaise Pascal de l'ENS de Lyon, Lyon, France
| | - Olivier Espeli
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, Université PSL, Paris, France
| | - Ralf Everaers
- École Normale Supérieure (ENS) de Lyon, CNRS, Laboratoire de Physique and Centre Blaise Pascal de l'ENS de Lyon, Lyon, France
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3
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Puentes-Rodriguez SG, Norcross J, Mera PE. To let go or not to let go: how ParA can impact the release of the chromosomal anchoring in Caulobacter crescentus. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.12.536610. [PMID: 37090538 PMCID: PMC10120649 DOI: 10.1101/2023.04.12.536610] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/25/2023]
Abstract
Chromosomal maintenance is vital for the survival of bacteria. In Caulobacter crescentus, chromosome replication initiates at ori and segregation is delayed until the nearby centromere-like region parS is replicated. Our understanding of how this sequence of events is regulated remains limited. The segregation of parS has been shown to involve multiple steps including polar release from anchoring protein PopZ, slow movement, and fast ParA-dependent movement to opposite cell pole. In this study, we demonstrate that ParA's competing attractions from PopZ and from DNA are critical for segregation of parS. Interfering with this balance of attractions - by expressing a variant ParA-R195E unable to bind DNA and thus favoring interactions exclusively between ParA-PopZ - results in cell death. Our data revealed that ParA-R195E's sole interactions with PopZ obstruct PopZ's ability to release the polar anchoring of parS resulting in cells with multiple parS loci fixed at one cell pole. We show that the inability to separate and segregate multiple parS loci from the pole is specifically dependent on the interaction between ParA and PopZ. Interfering with interactions between PopZ and the partitioning protein ParB, which is the interaction that anchors parS at the cell pole, does not rescue the ability of cells to separate the fixed parS loci when expressing parA-R195E. Thus, ParA and PopZ appear to have a distinct conversation from ParB yet can impact the release of ParB-parS from the anchoring at the cell pole. Collectively, our results reveal that the initial steps in chromosome segregation are highly regulated.
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Affiliation(s)
| | - J.D. Norcross
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Paola E. Mera
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
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4
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Mancini L, Crozat E, Javer A, Lagomarsino MC, Cicuta P. Dynamics of Bacterial Chromosomes by Locus Tracking in Fluorescence Microscopy. Methods Mol Biol 2022; 2476:155-170. [PMID: 35635703 DOI: 10.1007/978-1-0716-2221-6_12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
In the last two decades, it has been shown that bacterial chromosomes have remarkable spatial organization at various scales, and they display well-defined movements during the cell cycle, for example to reliably segregate daughter chromosomes. More recently, various labs have begun investigating also the short time dynamics (displacements during time intervals of 0.1 s-100 s), which should be related to the molecular structure. Probing these dynamics is analogous to "microrheology" approaches that have been applied successfully to study mechanical response of complex fluids. These studies of chromosome fluctuation dynamics have revealed differences of fluctuation amplitude across the chromosome, and different characters of motion depending on the time window of interest. Different fluctuation amplitudes have also been observed for the same chromosomal loci under antibiotic treatments, with magnitudes that are correlated to changes in intracellular density and thus crowding. We describe how to carry out tracking experiments of single loci and how to analyze locus motility. We point out the importance of considering in the analysis the number of GFP molecules per fluorescent locus, as well as the nature of the protein they are fused to, and also how to measure intracellular density.
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Affiliation(s)
- Leonardo Mancini
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Estelle Crozat
- Centre de Biologie Intégrative de Toulouse, Laboratoire de Microbiologie et de Génétique Moléculaires, Université de Toulouse, CNRS, UPS, Toulouse, France
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Avelino Javer
- Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, UK
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Marco Cosentino Lagomarsino
- IFOM, FIRC Institute of Molecular Oncology, Milan, Italy
- Physics Department, University of Milan, and INFN, Milan, Italy
| | - Pietro Cicuta
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge, UK.
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5
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Jewett AI, Stelter D, Lambert J, Saladi SM, Roscioni OM, Ricci M, Autin L, Maritan M, Bashusqeh SM, Keyes T, Dame RT, Shea JE, Jensen GJ, Goodsell DS. Moltemplate: A Tool for Coarse-Grained Modeling of Complex Biological Matter and Soft Condensed Matter Physics. J Mol Biol 2021; 433:166841. [PMID: 33539886 DOI: 10.1016/j.jmb.2021.166841] [Citation(s) in RCA: 113] [Impact Index Per Article: 37.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 01/19/2021] [Accepted: 01/20/2021] [Indexed: 02/01/2023]
Abstract
Coarse-grained models have long been considered indispensable tools in the investigation of biomolecular dynamics and assembly. However, the process of simulating such models is arduous because unconventional force fields and particle attributes are often needed, and some systems are not in thermal equilibrium. Although modern molecular dynamics programs are highly adaptable, software designed for preparing all-atom simulations typically makes restrictive assumptions about the nature of the particles and the forces acting on them. Consequently, the use of coarse-grained models has remained challenging. Moltemplate is a file format for storing coarse-grained molecular models and the forces that act on them, as well as a program that converts moltemplate files into input files for LAMMPS, a popular molecular dynamics engine. Moltemplate has broad scope and an emphasis on generality. It accommodates new kinds of forces as they are developed for LAMMPS, making moltemplate a popular tool with thousands of users in computational chemistry, materials science, and structural biology. To demonstrate its wide functionality, we provide examples of using moltemplate to prepare simulations of fluids using many-body forces, coarse-grained organic semiconductors, and the motor-driven supercoiling and condensation of an entire bacterial chromosome.
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Affiliation(s)
- Andrew I Jewett
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA.
| | | | - Jason Lambert
- Department of Chemistry, University of Tennessee, Knoxville, TN, USA
| | - Shyam M Saladi
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | | | | | - Ludovic Autin
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Martina Maritan
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Saeed M Bashusqeh
- School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
| | - Tom Keyes
- Department of Chemistry, Boston University, MA, USA
| | - Remus T Dame
- Leiden Institute of Chemistry, Leiden University, Leiden, Netherlands
| | - Joan-Emma Shea
- Departments of Chemistry and Biochemistry and Physics, University of California, Santa Barbara, CA, USA
| | - Grant J Jensen
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA; Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA, USA
| | - David S Goodsell
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA; RCSB Protein Data Bank and Institute for Quantitative Biomedicine, Rutgers, the State University of New Jersey, Piscataway, NJ, USA.
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6
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Spakowitz AJ. Polymer physics across scales: Modeling the multiscale behavior of functional soft materials and biological systems. J Chem Phys 2019; 151:230902. [DOI: 10.1063/1.5126852] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Affiliation(s)
- Andrew J. Spakowitz
- Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
- Biophysics Program, Stanford University, Stanford, California 94305, USA
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7
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Yildirim A, Feig M. High-resolution 3D models of Caulobacter crescentus chromosome reveal genome structural variability and organization. Nucleic Acids Res 2019. [PMID: 29529244 PMCID: PMC5934669 DOI: 10.1093/nar/gky141] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
High-resolution three-dimensional models of Caulobacter crescentus nucleoid structures were generated via a multi-scale modeling protocol. Models were built as a plectonemically supercoiled circular DNA and by incorporating chromosome conformation capture based data to generate an ensemble of base pair resolution models consistent with the experimental data. Significant structural variability was found with different degrees of bending and twisting but with overall similar topologies and shapes that are consistent with C. crescentus cell dimensions. The models allowed a direct mapping of the genomic sequence onto the three-dimensional nucleoid structures. Distinct spatial distributions were found for several genomic elements such as AT-rich sequence elements where nucleoid associated proteins (NAPs) are likely to bind, promoter sites, and some genes with common cellular functions. These findings shed light on the correlation between the spatial organization of the genome and biological functions.
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Affiliation(s)
- Asli Yildirim
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
| | - Michael Feig
- Department of Biochemistry & Molecular Biology, Michigan State University, MI 48824, USA
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8
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Abstract
Spatial organization is a hallmark of all living systems. Even bacteria, the smallest forms of cellular life, display defined shapes and complex internal organization, showcasing a highly structured genome, cytoskeletal filaments, localized scaffolding structures, dynamic spatial patterns, active transport, and occasionally, intracellular organelles. Spatial order is required for faithful and efficient cellular replication and offers a powerful means for the development of unique biological properties. Here, we discuss organizational features of bacterial cells and highlight how bacteria have evolved diverse spatial mechanisms to overcome challenges cells face as self-replicating entities.
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9
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Chremos A, Douglas JF. A comparative study of thermodynamic, conformational, and structural properties of bottlebrush with star and ring polymer melts. J Chem Phys 2018; 149:044904. [DOI: 10.1063/1.5034794] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Affiliation(s)
- Alexandros Chremos
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Jack F. Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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10
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Hacker WC, Li S, Elcock AH. Features of genomic organization in a nucleotide-resolution molecular model of the Escherichia coli chromosome. Nucleic Acids Res 2017. [PMID: 28645155 PMCID: PMC5570083 DOI: 10.1093/nar/gkx541] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
We describe structural models of the Escherichia coli chromosome in which the positions of all 4.6 million nucleotides of each DNA strand are resolved. Models consistent with two basic chromosomal orientations, differing in their positioning of the origin of replication, have been constructed. In both types of model, the chromosome is partitioned into plectoneme-abundant and plectoneme-free regions, with plectoneme lengths and branching patterns matching experimental distributions, and with spatial distributions of highly-transcribed chromosomal regions matching recent experimental measurements of the distribution of RNA polymerases. Physical analysis of the models indicates that the effective persistence length of the DNA and relative contributions of twist and writhe to the chromosome's negative supercoiling are in good correspondence with experimental estimates. The models exhibit characteristics similar to those of ‘fractal globules,’ and even the most genomically-distant parts of the chromosome can be physically connected, through paths combining linear diffusion and inter-segmental transfer, by an average of only ∼10 000 bp. Finally, macrodomain structures and the spatial distributions of co-expressed genes are analyzed: the latter are shown to depend strongly on the overall orientation of the chromosome. We anticipate that the models will prove useful in exploring other static and dynamic features of the bacterial chromosome.
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Affiliation(s)
- William C Hacker
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - Shuxiang Li
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - Adrian H Elcock
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
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11
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Krajina BA, Spakowitz AJ. Large-Scale Conformational Transitions in Supercoiled DNA Revealed by Coarse-Grained Simulation. Biophys J 2017; 111:1339-1349. [PMID: 27705758 DOI: 10.1016/j.bpj.2016.07.045] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Revised: 07/26/2016] [Accepted: 07/28/2016] [Indexed: 02/07/2023] Open
Abstract
Topological constraints, such as those associated with DNA supercoiling, play an integral role in genomic regulation and organization in living systems. However, physical understanding of the principles that underlie DNA organization at biologically relevant length scales remains a formidable challenge. We develop a coarse-grained simulation approach for predicting equilibrium conformations of supercoiled DNA. Our methodology enables the study of supercoiled DNA molecules at greater length scales and supercoiling densities than previously explored by simulation. With this approach, we study the conformational transitions that arise due to supercoiling across the full range of supercoiling densities that are commonly explored by living systems. Simulations of ring DNA molecules with lengths at the scale of topological domains in the Escherichia coli chromosome (∼10 kilobases) reveal large-scale conformational transitions elicited by supercoiling. The conformational transitions result in three supercoiling conformational regimes that are governed by a competition among chiral coils, extended plectonemes, and branched hyper-supercoils. These results capture the nonmonotonic relationship of size versus degree of supercoiling observed in experimental sedimentation studies of supercoiled DNA, and our results provide a physical explanation of the conformational transitions underlying this behavior. The length scales and supercoiling regimes investigated here coincide with those relevant to transcription-coupled remodeling of supercoiled topological domains, and we discuss possible implications of these findings in terms of the interplay between transcription and topology in bacterial chromosome organization.
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Affiliation(s)
- Brad A Krajina
- Department of Chemical Engineering, Stanford University, Stanford, California
| | - Andrew J Spakowitz
- Department of Chemical Engineering, Stanford University, Stanford, California; Department of Applied Physics, Stanford University, Stanford, California; Department of Materials Science and Engineering, Stanford University, Stanford, California; Biophysics Program, Stanford University, Stanford, California.
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12
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Schenk G, Krajina B, Spakowitz A, Doniach S. Potential for measurement of the distribution of DNA folds in complex environments using Correlated X-ray Scattering. MODERN PHYSICS LETTERS. B, CONDENSED MATTER PHYSICS, STATISTICAL PHYSICS, APPLIED PHYSICS 2016; 30:1650117. [PMID: 27127310 PMCID: PMC4846288 DOI: 10.1142/s0217984916501177] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In vivo chromosomal behavior is dictated by the organization of genomic DNA at length scales ranging from nanometers to microns. At these disparate scales, the DNA conformation is influenced by a range of proteins that package, twist and disentangle the DNA double helix, leading to a complex hierarchical structure that remains undetermined. Thus, there is a critical need for methods of structural characterization of DNA that can accommodate complex environmental conditions over biologically relevant length scales. Based on multiscale molecular simulations, we report on the possibility of measuring supercoiling in complex environments using angular correlations of scattered X-rays resulting from X-ray free electron laser (xFEL) experiments. We recently demonstrated the observation of structural detail for solutions of randomly oriented metallic nanoparticles [D. Mendez et al., Philos. Trans. R. Soc. B360 (2014) 20130315]. Here, we argue, based on simulations, that correlated X-ray scattering (CXS) has the potential for measuring the distribution of DNA folds in complex environments, on the scale of a few persistence lengths.
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Affiliation(s)
- Gundolf Schenk
- Geballe Lab for Advanced Materials, Stanford University, Stanford CA, USA
| | - Brad Krajina
- Department of Chemical Engineering, Stanford University, Stanford CA, USA
| | - Andrew Spakowitz
- Department of Chemical Engineering, Stanford University, Stanford CA, USA
| | - Sebastian Doniach
- Geballe Lab for Advanced Materials, Stanford University, Stanford CA, USA
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13
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Javer A, Lagomarsino MC, Cicuta P. Bacterial Chromosome Dynamics by Locus Tracking in Fluorescence Microscopy. Methods Mol Biol 2016; 1431:161-173. [PMID: 27283309 DOI: 10.1007/978-1-4939-3631-1_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Bacterial chromosomes have been shown in the last two decades to have remarkable spatial organization at various scales, and also well-defined movements during the cell cycle, for example, to reliably segregate daughter chromosomes. More recently, various labs have begun investigating the short-time dynamics (displacements during time intervals of 0.1-100 s), which one hopes to link to structure, in analogy to "microrheology" approaches applied successfully to study mechanical response of complex fluids. These studies of chromosome fluctuation dynamics have revealed differences of fluctuation amplitude across the chromosome, and different characters of motion depending on the time window of interest. The highly nontrivial motion at the shortest experimentally accessible times is still not fully understood in terms of physical models of DNA and cytosol. We describe how to carry out tracking experiments of single locus and how to analyze locus motility. We point out the importance of considering in the analysis the number of GFP molecules per fluorescent locus.
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Affiliation(s)
- Avelino Javer
- Cavendish Laboratory, University of Cambridge, Room 237, J.J. Thomson Avenue, Cambridge, CB3 0HE, UK
| | | | - Pietro Cicuta
- Cavendish Laboratory, University of Cambridge, Room 237, J.J. Thomson Avenue, Cambridge, CB3 0HE, UK.
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14
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The bacterial nucleoid: nature, dynamics and sister segregation. Curr Opin Microbiol 2015; 22:127-37. [PMID: 25460806 DOI: 10.1016/j.mib.2014.10.001] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Revised: 10/06/2014] [Accepted: 10/09/2014] [Indexed: 11/20/2022]
Abstract
Recent studies reveal that the bacterial nucleoid has a defined, self-adherent shape and an underlying longitudinal organization and comprises a viscoelastic matrix. Within this shape, mobility is enhanced by ATP-dependent processes and individual loci can undergo ballistic off-equilibrium movements. In Escherichia coli, two global dynamic nucleoid behaviors emerge pointing to nucleoid-wide accumulation and relief of internal stress. Sister segregation begins with local splitting of individual loci, which is delayed at origin, terminus and specialized interstitial snap regions. Globally, as studied in several systems, segregation is a multi-step process in which internal nucleoid state plays critical roles that involve both compaction and expansion. The origin and terminus regions undergo specialized programs partially driven by complex ATP burning mechanisms such as a ParAB Brownian ratchet and a septum-associated FtsK motor. These recent findings reveal strong, direct parallels among events in different systems and between bacterial nucleoids and mammalian chromosomes with respect to physical properties, internal organization and dynamic behaviors.
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15
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Imakaev MV, Fudenberg G, Mirny LA. Modeling chromosomes: Beyond pretty pictures. FEBS Lett 2015; 589:3031-6. [PMID: 26364723 DOI: 10.1016/j.febslet.2015.09.004] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 09/03/2015] [Indexed: 10/23/2022]
Abstract
Recently, Chromosome Conformation Capture (3C) based experiments have highlighted the importance of computational models for the study of chromosome organization. In this review, we propose that current computational models can be grouped into roughly four classes, with two classes of data-driven models: consensus structures and data-driven ensembles, and two classes of de novo models: structural ensembles and mechanistic ensembles. Finally, we highlight specific questions mechanistic ensembles can address.
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Affiliation(s)
- Maxim V Imakaev
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Geoffrey Fudenberg
- Graduate Program in Biophysics, Harvard University, Cambridge, MA 02138, USA; Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Leonid A Mirny
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Graduate Program in Biophysics, Harvard University, Cambridge, MA 02138, USA; Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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16
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Lagomarsino MC, Espéli O, Junier I. From structure to function of bacterial chromosomes: Evolutionary perspectives and ideas for new experiments. FEBS Lett 2015; 589:2996-3004. [PMID: 26171924 DOI: 10.1016/j.febslet.2015.07.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Revised: 06/29/2015] [Accepted: 07/01/2015] [Indexed: 12/11/2022]
Abstract
The link between chromosome structure and function is a challenging open question because chromosomes in vivo are highly dynamic and arduous to manipulate. Here, we examine several promising approaches to tackle this question specifically in bacteria, by integrating knowledge from different sources. Toward this end, we first provide a brief overview of experimental tools that have provided insights into the description of the bacterial chromosome, including genetic, biochemical and fluorescence microscopy techniques. We then explore the possibility of using comparative genomics to isolate functionally important features of chromosome organization, exploiting the fact that features shared between phylogenetically distant bacterial species reflect functional significance. Finally, we discuss possible future perspectives from the field of experimental evolution. Specifically, we propose novel experiments in which bacteria could be screened and selected on the basis of the structural properties of their chromosomes.
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Affiliation(s)
| | - Olivier Espéli
- CIRB-Collège de France, CNRS UMR 7241, INSERM U1050, Paris, France
| | - Ivan Junier
- Laboratoire Adaptation et Pathogénie des Micro-organismes - UMR 5163, Université Grenoble 1, CNRS, BP 170, F-38042 Grenoble Cedex 9, France; Centre for Genomic Regulation (CRG), Dr. Aiguader 88, 08003 Barcelona, Spain; Universitat Pompeu Fabra (UPF), Barcelona, Spain.
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17
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Weng X, Xiao J. Spatial organization of transcription in bacterial cells. Trends Genet 2014; 30:287-97. [PMID: 24862529 DOI: 10.1016/j.tig.2014.04.008] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Revised: 04/28/2014] [Accepted: 04/29/2014] [Indexed: 11/27/2022]
Abstract
Prokaryotic transcription has been extensively studied over the past half a century. However, there often exists a gap between the structural, mechanistic description of transcription obtained from in vitro biochemical studies, and the cellular, phenomenological observations from in vivo genetic studies. It is now accepted that a living bacterial cell is a complex entity; the heterogeneous cellular environment is drastically different from the homogenous, well-mixed situation in vitro. Where molecules are inside a cell may be important for their function; hence, the spatial organization of different molecular components may provide a new means of transcription regulation in vivo, possibly bridging this gap. In this review, we survey current evidence for the spatial organization of four major components of transcription [genes, transcription factors, RNA polymerase (RNAP) and RNAs] and critically analyze their biological significance.
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Affiliation(s)
- Xiaoli Weng
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Jie Xiao
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
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Muskhelishvili G, Travers A. Integration of syntactic and semantic properties of the DNA code reveals chromosomes as thermodynamic machines converting energy into information. Cell Mol Life Sci 2013; 70:4555-67. [PMID: 23771629 PMCID: PMC11113758 DOI: 10.1007/s00018-013-1394-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2013] [Revised: 05/28/2013] [Accepted: 05/29/2013] [Indexed: 11/29/2022]
Abstract
Understanding genetic regulation is a problem of fundamental importance. Recent studies have made it increasingly evident that, whereas the cellular genetic regulation system embodies multiple disparate elements engaged in numerous interactions, the central issue is the genuine function of the DNA molecule as information carrier. Compelling evidence suggests that the DNA, in addition to the digital information of the linear genetic code (the semantics), encodes equally important continuous, or analog, information that specifies the structural dynamics and configuration (the syntax) of the polymer. These two DNA information types are intrinsically coupled in the primary sequence organisation, and this coupling is directly relevant to regulation of the genetic function. In this review, we emphasise the critical need of holistic integration of the DNA information as a prerequisite for understanding the organisational complexity of the genetic regulation system.
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Affiliation(s)
- Georgi Muskhelishvili
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany,
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Le TB, Imakaev MV, Mirny LA, Laub MT. High-resolution mapping of the spatial organization of a bacterial chromosome. Science 2013; 342:731-4. [PMID: 24158908 PMCID: PMC3927313 DOI: 10.1126/science.1242059] [Citation(s) in RCA: 400] [Impact Index Per Article: 36.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Chromosomes must be highly compacted and organized within cells, but how this is achieved in vivo remains poorly understood. We report the use of chromosome conformation capture coupled with deep sequencing (Hi-C) to map the structure of bacterial chromosomes. Analysis of Hi-C data and polymer modeling indicates that the Caulobacter crescentus chromosome consists of multiple, largely independent spatial domains that are probably composed of supercoiled plectonemes arrayed into a bottle brush-like fiber. These domains are stable throughout the cell cycle and are reestablished concomitantly with DNA replication. We provide evidence that domain boundaries are established by highly expressed genes and the formation of plectoneme-free regions, whereas the histone-like protein HU and SMC (structural maintenance of chromosomes) promote short-range compaction and the colinearity of chromosomal arms, respectively. Collectively, our results reveal general principles for the organization and structure of chromosomes in vivo.
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Affiliation(s)
- Tung B.K. Le
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Maxim V. Imakaev
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Leonid A. Mirny
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Institute for Medical Engineering and Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Michael T. Laub
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Hensel Z, Weng X, Lagda AC, Xiao J. Transcription-factor-mediated DNA looping probed by high-resolution, single-molecule imaging in live E. coli cells. PLoS Biol 2013; 11:e1001591. [PMID: 23853547 PMCID: PMC3708714 DOI: 10.1371/journal.pbio.1001591] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Accepted: 05/09/2013] [Indexed: 11/19/2022] Open
Abstract
DNA looping mediated by transcription factors plays critical roles in prokaryotic gene regulation. The "genetic switch" of bacteriophage λ determines whether a prophage stays incorporated in the E. coli chromosome or enters the lytic cycle of phage propagation and cell lysis. Past studies have shown that long-range DNA interactions between the operator sequences O(R) and O(L) (separated by 2.3 kb), mediated by the λ repressor CI (accession number P03034), play key roles in regulating the λ switch. In vitro, it was demonstrated that DNA segments harboring the operator sequences formed loops in the presence of CI, but CI-mediated DNA looping has not been directly visualized in vivo, hindering a deep understanding of the corresponding dynamics in realistic cellular environments. We report a high-resolution, single-molecule imaging method to probe CI-mediated DNA looping in live E. coli cells. We labeled two DNA loci with differently colored fluorescent fusion proteins and tracked their separations in real time with ∼40 nm accuracy, enabling the first direct analysis of transcription-factor-mediated DNA looping in live cells. Combining looping measurements with measurements of CI expression levels in different operator mutants, we show quantitatively that DNA looping activates transcription and enhances repression. Further, we estimated the upper bound of the rate of conformational change from the unlooped to the looped state, and discuss how chromosome compaction may impact looping kinetics. Our results provide insights into transcription-factor-mediated DNA looping in a variety of operator and CI mutant backgrounds in vivo, and our methodology can be applied to a broad range of questions regarding chromosome conformations in prokaryotes and higher organisms.
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Affiliation(s)
- Zach Hensel
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Xiaoli Weng
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Arvin Cesar Lagda
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Jie Xiao
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
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Genome architecture and global gene regulation in bacteria: making progress towards a unified model? Nat Rev Microbiol 2013; 11:349-55. [DOI: 10.1038/nrmicro3007] [Citation(s) in RCA: 151] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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