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Radiosensitivity of DNA minicircles
F Culard1, M Spotheim-Maurizot, R Sabattier
1Centre de Biophysique Moléculaire, CNRS, Orléans, France.
International Journal of Radiation Biology
|June 1, 1994
Summary
DNA minicircles were studied at different twisting levels to assess their radiosensitivity. Untwisting the DNA helix did not alter its susceptibility to damage from gamma rays or neutrons, indicating consistent DNA radiosensitivity.
Area of Science:
- Molecular Biology
- Biophysics
- Radiation Biology
Background:
- DNA topology, specifically linking number (Lk), influences DNA structure and function.
- Small DNA circles (minicircles) exhibit limited flexibility, impacting their response to topological stress.
- Understanding DNA radiosensitivity is crucial for radiation therapy and radiation protection.
Purpose of the Study:
- To investigate the effect of DNA helix untwisting on radiosensitivity.
- To determine if changes in linking number affect DNA damage yields from ionizing radiation.
- To explore the structural adaptations of stressed DNA minicircles.
Main Methods:
- Construction of 207 bp DNA minicircles with varying linking numbers (Lk 20, 19, 18) using ethidium bromide.
- Irradiation of DNA minicircle topoisomers with gamma rays and fast neutrons.
- Quantification of single-strand breaks (SSBs) and double-strand breaks (DSBs) using alkaline elution techniques.
Main Results:
- Three distinct topoisomers were generated, differing in linking number and helical repeat.
- Undertwisted minicircles (Lk 19, 18) adopted a flat conformation due to limited supercoiling capacity.
- No significant differences in SSB or DSB yields were observed among the topoisomers upon irradiation.
Conclusions:
- DNA helix untwisting does not alter the radiosensitivity of DNA.
- The base and sugar moieties of DNA are equally susceptible to radical attack regardless of topological state.
- DNA radiosensitivity is independent of helix untwisting within the studied range.