DNA Produces Its Own "Sunscreen".

• Position: Brief Article

Researchers at Ohio State University, Columbus, have glimpsed for the first time how DNA protects itself from the sun's harmful radiation. Through a natural process that lasts less than one-trillionth of a second, light-absorbing parts of DNA convert ultraviolet (UV) radiation from the sun into heat. The speed of this process is the key to DNA's natural ability to protect itself from the sun's radiation, explains Bern Kohler, assistant professor of chemistry.

UV is harmful because it can cause DNA to mutate and trigger adverse conditions, including skin cancer and premature aging. DNA doesn't mutate every time people are exposed to sunlight, however. "From what we've seen, DNA functions somewhat like its own sunscreen," Kohler notes. "The process doesn't work perfectly every time, and that's when mutations take place--so don't stop wearing your sunscreen.

"For the first time, we've been able to see just how fast DNA dissipates UV energy, and that will help us better understand how light damages DNA." Previously, scientists had only indirect evidence that DNA rids itself of UV energy very quickly, because the process involved takes place much too fast to be viewed using conventional instruments.

Kohler and two of his graduate students took portions of the DNA molecule called nucleosides, placed them in water, and then bombarded them with an ultrashort pulse of UV light from a laser. The laser pulse lasted only 150 femtoseconds, or 150 quadrillionths of a second. The pulse deposited energy in the electrons of the nucleosides much as sunlight would, putting the nucleosides into an excited state. Because the laser...