scholarly journals Direct imaging of the circular chromosome in a live bacterium

2018 ◽  
Author(s):  
Fabai Wu ◽  
Aleksandre Japaridze ◽  
Xuan Zheng ◽  
Jacob W. J. Kerssemakers ◽  
Cees Dekker
Keyword(s):  
Spatial Organization ◽  
Quantitative Imaging ◽  
Origin Of Replication ◽  
Circular Chromosome ◽  
E Coli ◽  
Domain Boundaries ◽  
Transcription Regulators ◽  
And Function ◽  
Organizational Principles ◽  
Dna Density

New assays for quantitative imaging1–6 and sequencing7–11 have yielded great progress towards understanding the organizational principles of chromosomes. Yet, even for the well-studied model bacterium Escherichia coli, many basic questions remain unresolved regarding chromosomal (sub-)structure2,11, its mechanics1,2,12 and dynamics13,14, and the link between structure and function1,15,16. Here we resolve the spatial organization of the circular chromosome of bacteria by directly imaging the chromosome in live E. coli cells with a broadened cell shape. The chromosome was observed to exhibit a torus topology with a 4.2 μm toroidal length and 0.4 μm bundle thickness. On average, the DNA density along the chromosome shows dense right and left arms that branch from a lower-density origin of replication, and are connected at the terminus of replication by an ultrathin flexible string of DNA. At the single-cell level, the DNA density along the torus is found to be strikingly heterogeneous, with blob-like Mbp-size domains that undergo major dynamic rearrangements, splitting and merging at a minute timescale. We show that prominent domain boundaries at the terminus and origin of replication are induced by MatP proteins, while weaker transient domain boundaries are facilitated by the global transcription regulators HU and Fis. These findings provide an architectural basis for the understanding of the spatial organization of bacterial genomes.

scholarly journals Direct observation of independently moving replisomes in Escherichia coli

2019 ◽  
Author(s):  
Aleksandre Japaridze ◽  
Christos Gogou ◽  
Jacob W. J. Kerssemakers ◽  
Huyen My Nguyen ◽  
Cees Dekker
Keyword(s):  
Origin Of Replication ◽  
Train Track ◽  
Cell Width ◽  
Circular Chromosome ◽  
E Coli ◽  
Dna Segregation ◽  
Direct Support ◽  
A Cell ◽  
Genomic Material ◽  
Segregation Of Chromosomes

AbstractThe replication and transfer of genomic material from a cell to its progeny are vital processes in all living systems. Here we visualize the process of chromosome replication in E. coli cells with an increased width. Monitoring the replication of single chromosomes yields clear examples of replication bubbles that reveal that the two replisomes move independently from the origin to the terminus of replication along each of the two arms of the circular chromosome, providing direct support for the so-called train-track model, and against a factory model for replisomes. The origin of replication duplicates near midcell, initially splitting to random directions and subsequently towards the poles. The probability of successful segregation of chromosomes significantly decreases with increasing cell width, indicating that chromosome confinement by the cell boundary is an important driver of DNA segregation. Our findings resolve long standing questions in bacterial chromosome organization.

Structural similarity of ribosomes from E. coli and A. salina

1978 ◽  
Vol 36 (2) ◽  
pp. 242-243
Author(s):  
M. Boublik ◽  
R.M. Wydro ◽  
W. Hellmann ◽  
F. Jenkins
Keyword(s):  
Ribosomal Proteins ◽  
Direct Evidence ◽  
Structural Similarity ◽  
Carbon Support ◽  
Artemia Salina ◽  
Uranyl Acetate ◽  
Biological Assays ◽  
E Coli ◽  
And Function ◽  
Fine Carbon

Ribosomes are ribonucleoprotein particles necessary for processing the genetic information of mRNA into proteins. Analogy in composition and function of ribosomes from diverse species, established by biochemical and biological assays, implies their structural similarity. Direct evidence obtained by electron microscopy seems to be of increasing relevance in understanding the structure of ribosomes and the mechanism of their role in protein synthesis.The extent of the structural homology between prokaryotic and eukaryotic ribosomes has been studied on ribosomes of Escherichia coli (E.c.) and Artemia salina (A.s.). Despite the established differences in size and in the amount and proportion of ribosomal proteins and RNAs both types of ribosomes show an overall similarity. The monosomes (stained with 0.5% aqueous uranyl acetate and deposited on a fine carbon support) appear in the electron micrographs as round particles with a diameter of approximately 225Å for the 70S E.c. (Fig. 1) and 260Å for the 80S A.s. monosome (Fig. 2).

Structural Role of rRNAs on the Ribosomal Subunits from E. Coli by Scanning Transmission Electron Microscopy

1981 ◽  
Vol 39 ◽  
pp. 424-425
Author(s):  
M. Boublik ◽  
N. Robakis ◽  
J.S. Wall
Keyword(s):  
Three Dimensional ◽  
Uranyl Acetate ◽  
Dimensional Structure ◽  
Electron Microscopic ◽  
Ribosomal Subunits ◽  
E Coli ◽  
Freeze Dried ◽  
16S Rna ◽  
Scanning Transmission ◽  
And Function

The three-dimensional structure and function of biological supramolecular complexes are, in general, determined and stabilized by conformation and interactions of their macromolecular components. In the case of ribosomes, it has been suggested that one of the functions of ribosomal RNAs is to act as a scaffold maintaining the shape of the ribosomal subunits. In order to investigate this question, we have conducted a comparative TEM and STEM study of the structure of the small 30S subunit of E. coli and its 16S RNA.The conventional electron microscopic imaging of nucleic acids is performed by spreading them in the presence of protein or detergent; the particles are contrasted by electron dense solution (uranyl acetate) or by shadowing with metal (tungsten). By using the STEM on freeze-dried specimens we have avoided the shearing forces of the spreading, and minimized both the collapse of rRNA due to air drying and the loss of resolution due to staining or shadowing. Figure 1, is a conventional (TEM) electron micrograph of 30S E. coli subunits contrasted with uranyl acetate.

Depletion and Reconstitution of Active E. Coli Ribosomes

1975 ◽  
Vol 33 ◽  
pp. 640-641
Author(s):  
M. Boublik ◽  
W. Hellmann ◽  
F. Jenkins
Keyword(s):  
Protein Biosynthesis ◽  
Large Subunit ◽  
High Resolution Electron Microscopy ◽  
Small Subunit ◽  
Structure And Function ◽  
Biologically Active ◽  
Biological Macromolecules ◽  
E Coli ◽  
Resolution Electron ◽  
And Function

Correlations between structure and function of biological macromolecules have been studied intensively for many years, mostly by indirect methods. High resolution electron microscopy is a unique tool which can provide such information directly by comparing the conformation of biopolymers in their biologically active and inactive state. We have correlated the structure and function of ribosomes, ribonucleoprotein particles which are the site of protein biosynthesis. 70S E. coli ribosomes, used in this experiment, are composed of two subunits - large (50S) and small (30S). The large subunit consists of 34 proteins and two different ribonucleic acid molecules. The small subunit contains 21 proteins and one RNA molecule. All proteins (with the exception of L7 and L12) are present in one copy per ribosome.This study deals with the changes in the fine structure of E. coli ribosomes depleted of proteins L7 and L12. These proteins are unique in many aspects.

scholarly journals The Location of Substitutions and Bacterial Genome Arrangements

2020 ◽  
Author(s):  
Daniella F Lato ◽  
G Brian Golding
Keyword(s):  
Sinorhizobium Meliloti ◽  
Bacterial Genome ◽  
Evolutionary Analysis ◽  
Origin Of Replication ◽  
Ancestral Reconstruction ◽  
Molecular Change ◽  
E Coli ◽  
A Genome ◽  
The Impact ◽  
Molecular Evolutionary Analysis

Abstract Increasing evidence supports the notion that different regions of a genome have unique rates of molecular change. This variation is particularly evident in bacterial genomes where previous studies have reported gene expression and essentiality tend to decrease, while substitution rates usually increases with increasing distance from the origin of replication. Genomic reorganization such as rearrangements occur frequently in bacteria and allow for the introduction and restructuring of genetic content, creating gradients of molecular traits along genomes. Here, we explore the interplay of these phenomena by mapping substitutions to the genomes of Escherichia coli, Bacillus subtilis, Streptomyces, and Sinorhizobium meliloti, quantifying how many substitutions have occurred at each position in the genome. Preceding work indicates that substitution rate significantly increases with distance from the origin. Using a larger sample size and accounting for genome rearrangements through ancestral reconstruction, our analysis demonstrates that the correlation between the number of substitutions and distance from the origin of replication is often significant but small and inconsistent in direction. Some replicons had a significantly decreasing trend (E. coli and the chromosome of S. meliloti), while others showed the opposite significant trend (B. subtilis, Streptomyces, pSymA and pSymB in S. meliloti). dN, dS and ω were examined across all genes and there was no significant correlation between those values and distance from the origin. This study highlights the impact that genomic rearrangements and location have on molecular trends in some bacteria, illustrating the importance of considering spatial trends in molecular evolutionary analysis. Assuming that molecular trends are exclusively in one direction can be problematic.

scholarly journals DnaA, the Initiator of Escherichia coliChromosomal Replication, Is Located at the Cell Membrane

2000 ◽  
Vol 182 (9) ◽  
pp. 2604-2610 ◽  
Author(s):  
Gillian Newman ◽  
Elliott Crooke
Keyword(s):  
Cell Membrane ◽  
Spatial Organization ◽  
Active Form ◽  
Chromosomal Replication ◽  
E Coli ◽  
Dnaa Protein ◽  
Section Electron ◽  
Acidic Phospholipids

ABSTRACT Given the lack of a nucleus in prokaryotic cells, the significance of spatial organization in bacterial chromosome replication is only beginning to be fully appreciated. DnaA protein, the initiator of chromosomal replication in Escherichia coli, is purified as a soluble protein, and in vitro it efficiently initiates replication of minichromosomes in membrane-free DNA synthesis reactions. However, its conversion from a replicatively inactive to an active form in vitro occurs through its association with acidic phospholipids in a lipid bilayer. To determine whether the in situ residence of DnaA protein is cytoplasmic, membrane associated, or both, we examined the cellular location of DnaA using immunogold cryothin-section electron microscopy and immunofluorescence. Both of these methods revealed that DnaA is localized at the cell membrane, further suggesting that initiation of chromosomal replication in E. coli is a membrane-affiliated event.

scholarly journals Functional Studies of [FeFe] Hydrogenase Maturation in an Escherichia coli Biosynthetic System

2006 ◽  
Vol 188 (6) ◽  
pp. 2163-2172 ◽  
Author(s):  
Paul W. King ◽  
Matthew C. Posewitz ◽  
Maria L. Ghirardi ◽  
Michael Seibert
Keyword(s):  
Escherichia Coli ◽  
Catalytic Domain ◽  
Expression System ◽  
Iron Sulfur Cluster ◽  
Sulfur Cluster ◽  
E Coli ◽  
Functional Studies ◽  
Hydrogenase Maturation ◽  
Iron Sulfur ◽  
And Function

ABSTRACT Maturation of [FeFe] hydrogenases requires the biosynthesis and insertion of the catalytic iron-sulfur cluster, the H cluster. Two radical S-adenosylmethionine (SAM) proteins proposed to function in H cluster biosynthesis, HydEF and HydG, were recently identified in the hydEF-1 mutant of the green alga Chlamydomonas reinhardtii (M. C. Posewitz, P. W. King, S. L. Smolinski, L. Zhang, M. Seibert, and M. L. Ghirardi, J. Biol. Chem. 279:25711-25720, 2004). Previous efforts to study [FeFe] hydrogenase maturation in Escherichia coli by coexpression of C. reinhardtii HydEF and HydG and the HydA1 [FeFe] hydrogenase were hindered by instability of the hydEF and hydG expression clones. A more stable [FeFe] hydrogenase expression system has been achieved in E. coli by cloning and coexpression of hydE, hydF, and hydG from the bacterium Clostridium acetobutylicum. Coexpression of the C. acetobutylicum maturation proteins with various algal and bacterial [FeFe] hydrogenases in E. coli resulted in purified enzymes with specific activities that were similar to those of the enzymes purified from native sources. In the case of structurally complex [FeFe] hydrogenases, maturation of the catalytic sites could occur in the absence of an accessory iron-sulfur cluster domain. Initial investigations of the structure and function of the maturation proteins HydE, HydF, and HydG showed that the highly conserved radical-SAM domains of both HydE and HydG and the GTPase domain of HydF were essential for achieving biosynthesis of active [FeFe] hydrogenases. Together, these results demonstrate that the catalytic domain and a functionally complete set of Hyd maturation proteins are fundamental to achieving biosynthesis of catalytic [FeFe] hydrogenases.

Regulation and Function of Cellular Gene Products Involved in UV and Chemical Mutagenesis in E. Coli

1983 ◽  
pp. 181-202 ◽  
Author(s):  
Graham C. Walker ◽  
Stephen J. Elledge ◽  
Karen L. Perry ◽  
Anne Bagg ◽  
Cynthia J. Kenyon
Keyword(s):  
Chemical Mutagenesis ◽  
Gene Products ◽  
Cellular Gene ◽  
E Coli ◽  
And Function

scholarly journals Quantitative Imaging of Gut Microbiota Spatial Organization

2015 ◽  
Vol 18 (4) ◽  
pp. 478-488 ◽  
Author(s):  
Kristen A. Earle ◽  
Gabriel Billings ◽  
Michael Sigal ◽  
Joshua S. Lichtman ◽  
Gunnar C. Hansson ◽  
...  
Keyword(s):  
Gut Microbiota ◽  
Spatial Organization ◽  
Quantitative Imaging

scholarly journals Genetic Organization of the Vibrio harveyi dnaA Gene Region and Analysis of the Function of the V. harveyi DnaA Protein in Escherichia coli

2002 ◽  
Vol 184 (9) ◽  
pp. 2533-2538 ◽  
Author(s):  
Dvora Berenstein ◽  
Kirsten Olesen ◽  
Christian Speck ◽  
Ole Skovgaard
Keyword(s):  
Escherichia Coli ◽  
Promoter Region ◽  
Vibrio Harveyi ◽  
Gene Region ◽  
Chromosomal Dna ◽  
Dnaa Gene ◽  
E Coli ◽  
Dnaa Protein ◽  
Dam Methylase ◽  
And Function

ABSTRACT The Vibrionaceae family is distantly related to Enterobacteriaceae within the group of bacteria possessing the Dam methylase system. We have cloned, sequenced, and analyzed the dnaA gene region of Vibrio harveyi and found that although the organization of the V. harveyi dnaA region differs from that of Escherichia coli, the expression of both genes is autoregulated and ATP-DnaA binds cooperatively to ATP-DnaA boxes in the dnaA promoter region. The DnaA proteins of V. harveyi and E. coli are interchangeable and function nearly identically in controlling dnaA transcription and the initiation of chromosomal DNA replication despite the evolutionary distance between these bacteria.

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