Cerenkov Ultraviolet Radiation (¹³⁷Cs γ-rays) and Direct Excitation (¹³⁷Cs γ-rays and 50 kVp X-rays) Produce Photoreactivable Damage in Escherichia Coli

Summary

The mechanism of formation of photoreactivable damage in deoxyribonucleic acid (DNA) by ionizing radiation in a dark repair deficient strain of Escherichia coli (uvr A recA) has been investigated. By altering the ratio of damage produced directly (by ionization) to that formed indirectly (by Cerenkov ultraviolet (U.V.) radiation) by ¹³⁷Cs γ-rays, it has been demonstrated that the major portion of the photoreactivable damage is produced by Cerenkov U.V. radiation. The amount of photoreactivable damage produced by 50kVp X-rays, which cannot generate Cerenkov radiation, is similar to that component of photoreactivable damage produced by ¹³⁷Cs γ-rays that is not attributed to Cerenkov radiation. It is suggested that the second mechanism of formation of photoreactivable damage in DNA by ionizing radiation is the direct excitation of DNA. The possible role of Cerenkov U.V. radiation in ionizing radiation mutagenesis is discussed.