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Decrease in the linking number of plasmid DNA in dnaA mutants of Escherichia coli
T Mizushima1, J Tanino, T Miki
1Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
Biochemical and Biophysical Research Communications
|January 5, 1996
Summary
Temperature-sensitive dnaA mutants show reduced DNA linking numbers at 37°C, indicating impaired DNA replication initiation. This effect was confirmed to be caused by dnaA gene mutations.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- The dnaA gene is essential for initiating DNA replication in bacteria.
- Temperature-sensitive mutants allow for the study of essential genes under specific conditions.
Purpose of the Study:
- To investigate the role of the dnaA gene in DNA topology.
- To analyze the effect of dnaA mutations on plasmid linking numbers.
Main Methods:
- Agarose gel electrophoresis in the presence of chloroquine.
- Analysis of temperature-sensitive dnaA mutants (dnaA5, dnaA46).
- Complementation analysis and phage P1-mediated transduction.
Main Results:
- dnaA mutants exhibited a lower DNA linking number at the permissive temperature (37°C) compared to wild-type cells.
- No significant difference in linking number was observed at the non-permissive temperature (28°C).
- Mutations within the dnaA gene were confirmed as the cause of the reduced linking number.
Conclusions:
- The dnaA gene product plays a critical role in regulating DNA supercoiling and linking number.
- Impaired dnaA function affects DNA topology, particularly at higher temperatures.