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The helical repeat of underwound DNA in solution.
S M Richardson1, T C Boles, N R Cozzarelli
1Department of Molecular Biology, University of California, Berkeley 94720.
Nucleic Acids Research
|July 25, 1988
Summary
Researchers studied DNA structure using ethidium bromide to alter DNA winding. The helical repeat of DNA rings was directly measured and found to correlate with underwinding, matching mathematical predictions for supercoiled DNA.
Area of Science:
- Molecular Biology
- Biophysics
- Structural Biology
Background:
- DNA structure is influenced by supercoiling, affecting its biological functions.
- Ethidium bromide is a known intercalating agent that can alter DNA topology.
- Understanding DNA helical repeat is crucial for DNA replication and packaging.
Purpose of the Study:
- To investigate the relationship between DNA underwinding and its helical repeat.
- To validate mathematical models predicting DNA helical repeat in supercoiled states.
- To directly measure the helical repeat of DNA rings with controlled underwinding.
Main Methods:
- Relaxation of closed circular DNA using topoisomerase.
- Introduction of controlled underwinding using varying concentrations of ethidium bromide.
- Direct determination of DNA helical repeat using the Gaussian center method.
Main Results:
- The helical repeat of underwound DNA rings was found to vary predictably with the degree of underwinding.
- The observed helical repeat changes directly correlated with the helical repeat of relaxed, dye-free DNA.
- Results align with recent mathematical treatments predicting DNA helical repeat in supercoiled molecules.
Conclusions:
- The helical repeat of DNA is a direct function of its underwinding.
- Mathematical models accurately predict the helical repeat of supercoiled DNA in solution.
- This study provides direct experimental evidence for theoretical models of DNA structure.