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DNA supercoiling in gyrase mutants
Journal of Bacteriology
|May 1, 1984
Summary
Escherichia coli DNA supercoiling is disrupted by temperature-sensitive gyrA or gyrB mutations, causing nucleoid relaxation. This DNA relaxation is reversible in some mutants upon cooling, indicating temperature-dependent DNA supercoiling regulation.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Bacterial DNA is maintained in a supercoiled state by DNA gyrase.
- Temperature-sensitive mutations in gyrA or gyrB affect DNA gyrase function.
Purpose of the Study:
- To investigate the effect of temperature-sensitive gyrA and gyrB mutations on Escherichia coli nucleoid structure.
- To determine the reversibility of DNA relaxation in these mutants.
Main Methods:
- Isolation of nucleoids from Escherichia coli strains with temperature-sensitive gyrA or gyrB mutations.
- Sedimentation analysis of nucleoids in ethidium bromide-containing sucrose density gradients.
- Temperature shifts to restrictive and permissive conditions.
Main Results:
- Shift to restrictive temperature caused nucleoid DNA relaxation in all tested mutants.
- Three mutants showed reversible nucleoid relaxation upon cooling to 0°C.
- Nucleoid sedimentation rates increased by approximately 50% in three mutants at restrictive temperatures.
Conclusions:
- Temperature-sensitive gyrA and gyrB mutations lead to alterations in DNA supercoiling and nucleoid structure in Escherichia coli.
- The observed reversibility suggests a dynamic regulation of DNA supercoiling by DNA gyrase.
- These findings highlight the critical role of DNA gyrase in maintaining bacterial genome organization.
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