COLUMBUS , Ohio -- For the first time, scientists have observed DNA being damaged by ultraviolet (UV) light.

Ohio State University chemists and their colleagues in Germany used a special technique to watch strands of DNA in the laboratory sustain damage in real time.

They observed the most common chemical reaction among a family of reactions on the DNA molecule that are linked to sunburn, and discovered that this key reaction happens with astounding speed -- in less than one picosecond, or one millionth of one millionth of a second.

Scientists are studying UV damage to understand the role it plays in sunburn and diseases such as skin cancer. This new finding, reported in the current issue of the journal Science, shows that the damage depends greatly on the position of the DNA at the moment the UV strikes the molecule.

UV light excites the DNA molecule by adding energy, said Bern Kohler, associate professor of chemistry at Ohio State. Some exited energy states last a long time, and others a short time. The energy often decays away harmlessly, but occasionally it triggers a chemical reaction that alters the DNA's molecular structure.

Previously, scientists believed that the longer a DNA molecule was excited by UV energy, the greater the chance that it would sustain damage. So long-lived excited states were thought to be more dangerous than short-lived ones. But this study shows that the most common UV damage is caused by a very short-lived excited state.

"The speed of this reaction has important consequences for understanding how DNA is damaged by UV light," said Kohler. "In this study, we didn't see any evidence that long-lived energy states are responsible for damage. Now it seems more likely that short-lived states cause the most common chemical damage to DNA."

That damage consists of two tiny molecular bonds that form where they shouldn't -- between two thymine bases stacked together among
'"/>

Contact: Bern Kohler
Kohler@chemistry.ohio-state.edu
614-688-3944
Ohio State University
1-Feb-2007