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Electron microscopy of membrane-associated folded chromosomes of Escherichia coli
Abstract:
Membrane-associated folded chromosomes were purified from log-phase cultures of Escherichia coli 15 TAU-bar and prepared for electron microscopy by aqueous spreading techniques. A spectrum of structures was observed, ranging from condensed structures with no DNA fibers visible, to extended structures with DNA fibers. In the extended structures, loops of DNA radiated from residual envelope, the loops sometimes appeared supercoiled, and both their number and apparent contour length approximated previous estimates from physical and biochemical data. It is proposed that the structures with free DNA arose from the condensed structures.
Insights
Researchers visualized Escherichia coli folded chromosomes using electron microscopy. Extended DNA loops observed radiating from residual envelope structures support a model of chromosome decondensation.
Area of Science:
- Microbiology
- Molecular Biology
- Cell Biology
Background:
- The structure of the bacterial chromosome and its association with the cell envelope is crucial for cell function.
- Previous studies have provided physical and biochemical estimates for DNA loop size and number in Escherichia coli.
Purpose of the Study:
- To visualize the in situ structure of membrane-associated folded chromosomes from Escherichia coli.
- To compare observed DNA structures with existing physical and biochemical data.
Main Methods:
- Purification of membrane-associated folded chromosomes from log-phase Escherichia coli cultures.
- Electron microscopy using aqueous spreading techniques to prepare samples.
Main Results:
- A spectrum of chromosome structures was observed, from condensed to extended forms.
- Extended structures exhibited DNA loops radiating from residual envelope material.
- Observed DNA loop characteristics (number and contour length) aligned with previous estimates.
Conclusions:
- The observed DNA structures suggest a transition from condensed to extended forms.
- This provides visual evidence supporting models of bacterial chromosome organization and decondensation.