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The Escherichia coli nucleoid is shaped around replication and transcription [GCC]

ABSTRACT: 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.

ORGANISM(S): Escherichia coli

PROVIDER: GSE87117 | GEO | 2017/12/25

SECONDARY ACCESSION(S): PRJNA343606

REPOSITORIES: GEO

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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.

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The Escherichia coli nucleoid is shaped around replication and transcription [GCC]

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