BERKELEY, CA Ionizing radiation, toxic chemicals, and other agents continually damage the body's DNA, threatening life and health: unrepaired DNA can lead to mutations, which in turn can lead to diseases like cancer. Intricate DNA repair mechanisms in the cells' nuclei are constantly working to fix what's broken, but whether the repair work happens "on the road" right where the damage occurs or "in the shop" at specific regions of the nucleus is an unanswered question.
That question may now be closer to an answer. By comparing computer models of damaged human DNA with microscopic images of human cells that reveal focal sites of radiation-induced damage, researchers in the Life Sciences Division (LSD) of the Department of Energy's Lawrence Berkeley National Laboratory, with colleagues at NASA and the Universities Space Research Association, have found evidence that indeed there are specific regions where broken DNA is concentrated for repair.
"NASA has long been interested in the radiation hazards in space," says LSD's Sylvain Costes, who led the study. "On a trip to Mars, astronauts will be exposed to cosmic rays for as long as three years, so NASA has been trying to come up with a mechanistic model of DNA repair to estimate the increased risk of cancer. We are helping to develop such a model."
Double-strand breaks and radiation-induced foci
In many NASA studies cells have been exposed to particles like those found in cosmic rays, such as energetic iron nuclei produced in accelerators at Brookhaven National Laboratory. The goal is to determine how many double-strand breaks (DSBs) in which both strands of the DNA double helix are severed occur per gray of radiation. (One gray is equivalent to 100 rads, an older unit signifying "radiation absorbed dose"; a gray equals one joule of energy absorbed per kilogram of matter.)