The Escherichia coli nucleoid is shaped around replication and transcription [RNA-Seq]
Ontology highlight
ABSTRACT:
ORGANISM(S): Escherichia coli
PROVIDER: GSE87071 | GEO | 2017/12/25
SECONDARY ACCESSION(S): PRJNA343424
REPOSITORIES: GEO
Similar Datasets
Project description:The Escherichia coli nucleoid is confined within a rod shaped cell many times smaller than the outstretched chromosome. While extensive compaction is necessary for this process, the chromosome must at the same time remain accessible to essential cellular processes such as replication and transcription. Currently, the individual contributions of cellular confinement, chromosome topology, replication and transcription on nucleoid organization are not well understood. Here we synchronize E. coli cells in stationary phase, where replication has ceased, each cell contains only one copy of the chromosome, and transcription is minimal. We then release the cells and capture chromosome contacts and transcription immediately following release and through-out one cell cycle. Polymer models of confined and topologically constrained circular polymers revealed that cellular confinement and topology do not contribute extensively to the organization of the E. coli nucleoid. Rather, local nucleoid structure is established concurrent with replication, and higher order organization is formed by the replication dependant clustering of linearly distant SeqA bound sites and cell cycle specific gene transcription.
2017-12-25 | GSE87117 | GEO
Project description:To fit within the confines of the cell, bacterial chromosomes are highly condensed into a structure called the nucleoid. Despite the high degree of compaction in the nucleoid, the genome remains accessible to essential biological processes, such as replication and transcription. Here, we present the first high-resolution chromosome conformation capture-based molecular analysis of the spatial organization of the Escherichia coli nucleoid during rapid growth in rich medium and following an induced amino acid starvation that promotes the stringent response. Our analyses identify the presence of origin and terminus domains in exponentially growing cells. Moreover, we observe an increased number of interactions within the origin domain and significant clustering of SeqA-binding sequences, suggesting a role for SeqA in clustering of newly replicated chromosomes. By contrast, ‘histone-like’ protein (i.e. Fis, IHF and H-NS) binding sites did not cluster, and their role in global nucleoid organization does not manifest through the mediation of chromosomal contacts. Finally, genes that were downregulated after induction of the stringent response were spatially clustered, indicating that transcription in E. coli occurs at transcription foci.
2013-05-01 | GSE40304 | GEO
Project description:To fit within the confines of the cell, bacterial chromosomes are highly condensed into a structure called the nucleoid. Despite the high degree of compaction in the nucleoid, the genome remains accessible to essential biological processes, such as replication and transcription. Here, we present the first high-resolution chromosome conformation capture-based molecular analysis of the spatial organization of the Escherichia coli nucleoid during rapid growth in rich medium and following an induced amino acid starvation that promotes the stringent response. Our analyses identify the presence of origin and terminus domains in exponentially growing cells. Moreover, we observe an increased number of interactions within the origin domain and significant clustering of SeqA-binding sequences, suggesting a role for SeqA in clustering of newly replicated chromosomes. By contrast, ‘histone-like’ protein (i.e. Fis, IHF and H-NS) binding sites did not cluster, and their role in global nucleoid organization does not manifest through the mediation of chromosomal contacts. Finally, genes that were downregulated after induction of the stringent response were spatially clustered, indicating that transcription in E. coli occurs at transcription foci. A 4 chips study of exponentially growing wild type E. coli strain MG1655 grown in LB rich media or after induction of the stringent response by serine hydroxamate for 30 min. Two technical replicates, Three biological replicates mixed prior hybridization on the chip.
2013-05-01 | E-GEOD-40304 | biostudies-arrayexpress
Project description:Chromosomes are composed of enormously long DNA molecules which must be distributed correctly as the cells grow and divide. In Escherichia coli the new DNA behind the replication forks is specifically bound by the SeqA protein. SeqA binds to GATC sequences which are methylated on the A of the old strand but not on the new strand. Binding lasts for a period of time until Dam methyltransferase methylates the new strand. It is therefore believed that a region of hemi-methylated DNA covered by SeqA follows the replication fork. We show that this is indeed the case by using global ChIP on Chip analysis and a newly developed method for methylation analysis. A comparison of rapid and slow growth conditions showed that in cells with multiple replication forks per chromosome, the old forks bind little SeqA. Analysis of strains with strong SeqA binding sites at different chromosomal loci supported this finding. The results indicate that a re-organization of the chromosome occurs at a timepoint when new forks have travelled about 20% and old forks about 75% of the way to the terminus. This timepoint coincides with the end of origin sequestration. It is so far not known what brings about the end of origin sequestration. Here we suggest that a reorganization event occurs resulting in both origin desequestration and loss of old replication forks from the SeqA structures. SeqA ChIP-Chip analysis of unsynchronized E. coli MG1655 and in cells synchronized regarding initiation of DNA replication; SeqA ChIP-Chip of Dam overproducing strain and SeqA4 mutant; SeqA ChIP-Chip of strains with chromosomal insertions of strong SeqA binding site. Methylation analysis of synchronized E. coli MG1655dnaC2 cells 0 and 15 min after initiation.
2012-02-22 | E-GEOD-28280 | biostudies-arrayexpress
Project description:Chromosomes are composed of enormously long DNA molecules which must be distributed correctly as the cells grow and divide. In Escherichia coli the new DNA behind the replication forks is specifically bound by the SeqA protein. SeqA binds to GATC sequences which are methylated on the A of the old strand but not on the new strand. Binding lasts for a period of time until Dam methyltransferase methylates the new strand. It is therefore believed that a region of hemi-methylated DNA covered by SeqA follows the replication fork. We show that this is indeed the case by using global ChIP on Chip analysis and a newly developed method for methylation analysis. A comparison of rapid and slow growth conditions showed that in cells with multiple replication forks per chromosome, the old forks bind little SeqA. Analysis of strains with strong SeqA binding sites at different chromosomal loci supported this finding. The results indicate that a re-organization of the chromosome occurs at a timepoint when new forks have travelled about 20% and old forks about 75% of the way to the terminus. This timepoint coincides with the end of origin sequestration. It is so far not known what brings about the end of origin sequestration. Here we suggest that a reorganization event occurs resulting in both origin desequestration and loss of old replication forks from the SeqA structures.
2012-02-22 | GSE28280 | GEO
Project description:As in Eukaryotes, bacterial genomes are not randomly folded. Bacterial genetic information is generally carried on a circular chromosome with a single origin of replication from which two replication forks proceed bidirectionaly towards the opposite terminus region. Here we investigate the higher-order architecture of the Escherichia coli genome, showing its partition into two structuraly distinct entities by a complex and intertwined network of contacts: the replication terminus (ter) region and the rest of the chromosome. Outside ter, the condensin MukBEF and the ubiquitous nucleoid-associated protein (NAP) HU promote DNA contacts in the megabase range. Within ter, the MatP protein prevents MukBEF activity and contacts are restricted to ~280 kb creating a domain with distinct structural properties. We also show how other NAPs contribute to nucleoid organization, such as H-NS that restricts short-range interactions. Combined, these results reveal the contributions of major, evolutionary conserved proteins in a bacterial chromosome organization.
2017-12-07 | GSE107301 | GEO
Project description:Nucleoid remodeling facilitated by DNA supercoiling results in changes in nucleoid configuration and involves nucleoid-associated proteins (NAPs) and structural maintenance of chromosomes (SMC) proteins among others. Changes in nucleoid configurations regulated by NAPs are synchronized with cellular adaptation and influence the simultaneous expression of several genes. HU, a ubiquitous bacterial histone-like protein, is among the most conserved and abundant NAPs in eubacteria. In Escherichia coli, HU forms dimers by HUα self-association (HUαα) or by HUα-HUβ interactions (HUαβ). HUα is mostly expressed during lag and early exponential growth phase and HUβ is expressed only during the later exponential and stationary phase, pointing to distinct HUαα/DNA and HUαβ/DNA packaging of the nucleoid in regulating expression patterns during growth and stasis. Mutations or the deletion of HU transform the E. coli nucleoid to a different form and alter overall transcription program; thus, HU interactions with DNA directly affect global gene regulation. Recently, analysis of high-resolution contact maps of the E. coli nucleoid revealed an important role of HU to promote long-range DNA-DNA contacts within the nucleoid. Yet, the molecular connections between HU-DNA interactions and changes in nucleoid architecture that regulate gene expression globally remain unknown. Here, we explored the higher-order E. coli nucleoid organization by soft x-ray tomography (SXT) and revealed an effect of HU surface charges in overall nucleoid organization and rearrangements. We also studied global transcription by next-generation RNA sequencing (RNA-Seq) and found a link between nucleoid rearrangement and changes in global transcription. To determine the functional relationships of observed nucleoid rearrangement and HU-DNA interactions, we also characterized the overall organization of HU nucleoprotein complexes in solution by small angle x-ray scattering (SAXS). We found that HUαα-mediated DNA networks are different at different ionic strengths and pHs. By means of macromolecular crystallography, we additionally elucidate HUαα dependent molecular switches that modulate DNA networking. This integrative structural study explains how HUαα regulates dynamic transformations of the nucleoid by DNA bridging to control nucleoid rearrangement and global gene regulation.
2020-04-01 | GSE134667 | GEO
Project description:Plastids contain multiple copies of the plastid chromosome, folded together with proteins and RNA into nucleoids. The degree to which components of the plastid gene expression and protein biogenesis machineries are nucleoid associated, and the factors involved in plastid DNA organization, repair, and replication, are poorly understood. To provide a conceptual framework for nucleoid function, we characterized the proteomes of highly enriched nucleoid fractions of proplastids and mature chloroplasts isolated from the maize (Zea mays) leaf base and tip, respectively, using mass spectrometry. Quantitative comparisons with proteomes of unfractionated proplastids and chloroplasts facilitated the determination of nucleoid-enriched proteins. This nucleoid-enriched proteome included proteins involved in DNA replication, organization, and repair as well as transcription, mRNA processing, splicing, and editing. Many proteins of unknown function, including pentatricopeptide repeat (PPR), tetratricopeptide repeat (TPR), DnaJ, and mitochondrial transcription factor (mTERF) domain proteins, were identified. Strikingly, 70S ribosome and ribosome assembly factors were strongly overrepresented in nucleoid fractions, but protein chaperones were not. Our analysis strongly suggests that mRNA processing, splicing, and editing, as well as ribosome assembly, take place in association with the nucleoid, suggesting that these processes occur cotranscriptionally. The plastid developmental state did not dramatically change the nucleoid-enriched proteome but did quantitatively shift the predominating function from RNA metabolism in undeveloped plastids to translation and homeostasis in chloroplasts. This study extends the known maize plastid proteome by hundreds of proteins, including more than 40 PPR and mTERF domain proteins, and provides a resource for targeted studies on plastid gene expression. Details of protein identification and annotation are provided in the Plant Proteome Database.
2023-09-28 | PXD045331 | Pride
Project description:The stringent response enables bacteria to respond to a variety of environmental stresses, especially various forms of nutrient limitation. During the stringent response the cell produces large quantities of the nucleotide alarmone ppGpp, which modulates many aspects of cell physiology, including reprogramming transcription, blocking protein translation, and inhibiting new rounds of DNA replication. The mechanism by which ppGpp inhibits DNA replication initiation in Escherichia coli remains unclear. Prior work suggested that ppGpp blocks new rounds of DNA replication by inhibiting transcription of the essential initiation factor dnaA, but we found that replication is still inhibited by ppGpp in cells ectopically producing DnaA. Instead, we provide evidence that a global reduction of transcription by ppGpp prevents replication initiation by modulating the supercoiling state of the origin of replication, oriC. Active transcription normally introduces negative supercoils into oriC to help promote replication initiation, so the accumulation of ppGpp reduces initiation potential at oriC. We find that maintaining transcription near oriC, either by expressing a ppGpp-blind RNA polymerase mutant or by inducing transcription from a ppGpp-insensitive promoter, can strongly bypass the inhibition of replication by ppGpp. Additionally, we show that increasing global negative supercoiling by inhibiting topoisomerase I or by deleting the nucleoid-associated protein seqA, also relieves inhibition. We propose a model, potentially conserved across proteobacteria, in which ppGpp indirectly creates an unfavorable energy landscape for initiation by preventing the introduction of negative supercoils into oriC.
2019-06-11 | GSE128606 | GEO
Project description:In Escherichia coli crosstalk between DNA supercoiling, nucleoid-associated proteins and major RNA polymerase σ initiation factors regulates growth phase-dependent gene transcription. We show that the highly conserved spatial ordering of relevant genes along the chromosomal replichores largely corresponds both to their temporal expression patterns during growth and to an inferred gradient of DNA superhelical density from the origin to the terminus. Genes implicated in similar functions are related mainly in trans across the chromosomal replichores, whereas DNA-binding transcriptional regulators interact predominantly with targets in cis along the replichores. We also demonstrate that macrodomains (the individual structural partitions of the chromosome) are regulated differently. We infer that spatial and temporal variation of DNA superhelicity during the growth cycle coordinates oxygen and nutrient availability with global chromosome structure, thus providing a mechanistic insight into how the organization of a complete bacterial chromosome encodes a spatiotemporal program integrating DNA replication and global gene expression.
2017-01-01 | GSE65244 | GEO