SINGLE-STRAND BREAKS INDUCED IN DNA BY VACUUM-ULTRAVIOLET RADIATION

Abstract— The efficiency of vacuum u.v. for producing single-strand breaks in DNA was determined for wavelengths between 58 and 254 nm (corresponding to photon energies of 21·2 and 4·9 eV, respectively) by using the supertwisted RF-DNA of bacteriophage φX174. The cross-section for production of single-strand breaks increases continuously by about 5 orders of magnitude between 5 and 10 eV photon energy, whereas from 11 to 21 eV the number of strand breaks produced per unit of incident radiation energy is approximately constant. Thus, absorption of a 10-eV photon causes DNA strand breaks with maximum efficiency. In addition, the number of electrons liberated from DNA by photons below 10 eV is one or two orders of magnitude higher than the frequency of strand breaks, demonstrating that in this energy range only a small fraction of the ionizations leads to strand breakage in DNA.