Radiation Sensitivity of Cells and Base Composition of DNA: An Electron Spin Resonance Study

Kaplan and Zavarine (1) have reported that the X-ray sensitivity of eight different bacterial species irradiated in suspension increases linearly with the relative guanine-cytosine (GC) content of their DNA. Since there is convincing evidence that DNA is the most important target responsible for reproductive death in cells exposed to ionizing radiation (2-5), it was reasonable to assume (1) that the radiosensitivity of DNA is related to its base ratio. This view is supported by recent studies on isolated DNA indicating that the radiosensitivity of different genetic markers, as measured in transformation experiments, is related to differences in their GC content (2). The molecular mechanisms responsible for the apparent relationship between radiosensitivity and base composition have not yet been elucidated. Attempts have been made to gain information concerning the inherent radiosensitivity of DNA preparations with different base ratios. For this purpose qualitative and quantitative electron spin resonance (ESR) studies have been carried out on different DNA preparations as well as on DNA constituents. The results indicate that in the guanine-cytosine pair the yield of radicals is higher and their stability is less than in the adenine-thymine (AT) base pair.