In the current issue of the journal Nature, Bern Kohler and his colleagues report that DNA dissipates the energy from ultraviolet (UV) radiation in a kind of energy wave that travels up the edge of the DNA molecule, as if the energy were climbing one side of the helical DNA "ladder."

The finding lends insight into how DNA damage occurs along the ladder's edge.

It also counters what scientists proposed in the 1960s: that UV causes mutations by damaging the bonds between base pairs the horizontal "rungs" on the ladder. The new study shows that UV energy moves vertically, between successive bases.

In undamaged DNA, there are no chemical bonds between vertically stacked bases. But the bases do interact electronically, which is why Kohler thinks they form an efficient conduit for UV energy to flow through.

"Even though paired bases are connected by weak chemical bonds, it's the interactions that take place without chemical bonds the interactions between stacked bases that are much more important for dissipating UV energy," Kohler said.

The Nature paper builds on work from five years ago, when the associate professor of chemistry and his team first discovered that single DNA bases convert harmful UV energy to heat to prevent sun damage in the same way that sunscreen molecules protect sunbathers.

Back then, they studied only single bases floating in water. They hit the bases with a kind of UV strobe light, and saw that the energy was released as heat in less than one trillionth of a second.

Their new experiments show that the behavior of full DNA differs profoundly from that of isolated bases. When the chemists turned their strobe light on whole strands of novel DNA, the UV energy still changed
'"/>

Contact: Bern Kohler
Kohler.40@osu.edu
614-688-3944
Ohio State University
24-Aug-2005