Single- and Double-strand Breaks in pBR322 DNA by Vacuum-UV from 8.3 to 20.7 eV

• Published in: JOURNAL OF RADIATION RESEARCH 1994, Vol.35 (2), p.104-111
• Main Authors: Hieda, K, Suzuki, K, Hirono, T, Suzuki, M, Furusawa, Y
• Format: Article
• Language: English
• Subjects: DNA - radiation effects; DNA Damage - radiation effects; DNA, Single-Stranded - radiation effects; Electrophoresis, Agar Gel; Radiation Dosage; Ultraviolet Rays - adverse effects; Vacuum
• ISSN: 0449-3060; 1349-9157
• DOI: 10.1269/jrr.35.104

Solid pBR322 DNA was irradiated in a vacuum by monochromatic photons from 8.3 eV (150 nm) to 20.7 eV (60 nm), and the formation of single- and double-strand breaks (ssb and dsb) was determined using agarose gel electrophoresis. The action cross sections increased 20 times (ssb) and 43 times (dsb) from 8.3 eV to 20.7 eV; the quantum yields increased 5.4 times (ssb) and 12 times (dsb). The cross sections for dsb were 0.0059 at 8.3 eV and 0.013 at 20.7 eV of those of ssb; these values were smaller than about 0.04 for 2.1 keV photons, or about 0.18 for 60Co γ-rays. Although vacuum UV photons were proved to induce dsb, they had a lower efficiency than when using soft X-rays or γ-rays. Since the first ionization potentials of DNA constituent molecules are around 9 eV1), the mode of the energy-absorbing process changes from excitation to superexcitation, and finally to ionization, as the photon energy becomes large2, 3).