By Jo McCulty Bern Kohler examines how DNA protects itself from UV radiation.

Ultrafast laser pulses reveal DNA's natural 'sunscreen'

Researchers at Ohio State 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 key to DNA's natural ability to protect itself from the sun's radiation, said Bern Kohler, assistant professor of chemistry.

UV is harmful because it can cause DNA to mutate and cause conditions that include skin cancer and premature aging, Kohler explained. But our DNA doesn't mutate every time we're exposed to sunlight.

"From what we've seen, DNA functions somewhat like its own sunscreen," said Kohler. "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," he continued.

Previously, scientists had only indirect evidence that DNA rids itself of UV energy very quickly, because the processes involved take place much too quickly to be viewed using conventional instruments.

Kohler and two of his graduate students, Jean-Marc Pecourt and Jorge Peon, took portions of the DNA molecule called nucleosides, placed them in water, and bombarded them with an ultrashort pulse of UV light from a laser. The pulse deposited energy in the electrons of the nucleosides much as sunlight would, putting the nucleosides into an excited state.

Because the laser pulses were so short, the researchers were able to study the extremely rapid process by which DNA changes energy from UV radiation into heat.

In a fraction of a trillionth of a second, the electronic energy was transformed into increased vibrational motion of the nucleoside's atoms Ñ heat. The nucleoside's temperature jumped to more than 1,300 degrees Celsius. It cooled down again by transferring energy to the much cooler water molecules that surrounded it. The researchers found that the cooling process finished in only a few trillionths of a second.

Kohler said that while our DNA may reach a high temperature during this reaction, the timing is so brief, we can't feel it.

He speculates that the speed of the process is critical for protecting DNA. "The longer the excited state energy remains localized in DNA, the greater the chance for permanent damage," he said.

This method of protecting DNA is probably universal to life on Earth, Kohler said. The nucleosides he and his students used in the lab are the same building blocks found in the genetic material of all plants and animals. The water surrounding the nucleosides in the lab simulated the water found in plant and animal cells.

"We had to look at a component of DNA to start, but eventually it will be important for us to look at the whole DNA molecule," he added.

In addition to their importance for cancer research, the findings may help researchers design better sunscreens for people and photostabilizers for paints. Photostabilizers are compounds that protect paint, plastics and other materials from damage by UV light.

To Kohler, the results also say something about how life evolved on this planet. The early Earth had a much different atmosphere, he explained, so early life would have had to withstand much more UV radiation than we are exposed to today.

"Today, ozone in the stratosphere protects us from most UV radiation, so scientists have wondered how life could have withstood that early onslaught. The fact that DNA functions very much like its own sunscreen may have been a critical factor in the evolution of life," he said.

New anesthetic promises better pain control for patients

An Ohio State researcher has patented a dental anesthetic that's considerably more effective than any currently available. The formula is a mix of a local anes-thetic agent and a sugar alcohol. The alcohol opens the protective covering of sensory nerves, allowing the anesthetic agent to enter the innermost parts of the nerves it is meant to numb. Researchers found that the new composition could completely numb the anesthetized region in about 90 percent of cases, said Al Reader, professor of dentistry.

'Gatekeeper' protein is key to cellular life

Researchers are surprised by their determination that a seemingly ordinary protein called YidC found within the membranes of bacteria serves as a gatekeeper of sorts, allowing into the membrane other proteins essential for the bacteria to live. When YidC isn't present, the bacteria die. The new discovery may suggest a completely new pathway for the translocation of proteins within basic biological units, said Ross Dalbey, professor of chemistry.