Discover Brookhaven

New Method Offers Insight Into Radiation Damage to DNA

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Damaging the Double Helix

NASA Space Radiation Laboratory

Built and operated by NASA in cooperation with DOE, NSRL employs beams of heavy ions extracted from Brookhaven accelerators to irradiate a variety of biological specimens (including tissues, cells, and DNA), as well as industrial materials being studied for their suitability for space suits and spacecraft shielding. More...

Photo of student researchers

Students participating in the space radiation summer program at NSRL.

Radiation can damage the DNA “double helix” — a two-stranded, twisting molecule — in a variety of ways: 1) by knocking off one or more of the DNA “bases” known by the letters A, T, G, and C, which form the bonds between the two strands; 2) by oxidizing these bases; or 3) by breaking through one or both strands. All can result in a failure of the molecule to perform its main task —telling cells which proteins to make. That can lead to out-of-control cell growth (cancer) or death.

Cells can often repair radiation-damaged DNA, using specialized enzymes to excise and patch up the damaged segments. But damage from ionizing particle radiation appears to be harder to repair than that caused by lower-energy forms of radiation such as x-rays and gamma rays.

Scientists have long hypothesized that the reason forthis difference was that the high-energy ionizing particles caused more complex damage containing many lesions close together on the DNA, leading to slower and less-accurate repair. The technique developed by Sutherland and Paap allowed them to test this hypothesis.

Using standard techniques of molecular biology, thescientists created synthetic DNA with known lesionsin a variety of spatial arrangements with a red fluorescent tag attached to one end of the strand and a greenfluorescent tag at the other end. They then applieda DNA repair enzyme, which clips the DNA atdamaged sites.

The scientists then used gel electrophoresis to separatethe fragments according to their lengths. By looking at the red- and green-tagged bands, and determining their lengths, the scientists were able to measure how well the repair enzyme recognized and repaired the DNA damage.