Energy Requirements for Damaging DNA Molecules

Summary

Strand break formation and biological inactivation of infectious DNA of bacteriophage ΦX 174 exposed to vacuum-ultra-violet radiation of 4·9 to 21·2 eV quantum energy is investigated. At 21·2 eV as many as 84 per cent of the DNA molecules are inactivated by breaks whereas breaks do not contribute to inactivation at 4·9 eV. The quantum yield of break formation increases from 1·7 × 10⁻⁵ (4·9 eV) to 0·55 (21·2 eV) and shows a dependence on energy similar to that of electron emission (due to ionization) above 8 eV. The mechanisms leading to break formation and inactivation are discussed taking the absorption spectrum of DNA in the vacuum-ultra-violet region into consideration.