The molecular basis for radiation effects on cells.

The field of radiobiology was built on the premise that radiation is dangerous because of its damaging effects on DNA, where only a few events, or even a single event, at the molecular level can inactivate cells (Hutchinson 1966). The discordance of modern radiation toxicity models with results spanning nearly 5 decades of research on the extremely radiation-resistant bacterium Deinococcus radiodurans is reviewed. Much of the early data implicating DNA itself were for bacterial systems. However, recent studies show that extreme resistance to gamma radiation among bacteria consistently coincides with a greatly diminished susceptibility to protein oxidation but with similar DNA lesion-yields as other organisms. A growing body of experimental evidence now supports that naturally sensitive bacteria are killed by radiation mainly owing to protein oxidation, whereas extreme resistance in bacteria is achieved by protecting enzymes and the repair functions they catalyze. Based on new insights, the prospects for exporting the radioprotective mechanisms outside of D. radiodurans for practical purposes are considered.