Critical energies for SSB and DSB induction in plasmid DNA by low-energy photons: action spectra for strand-break induction in plasmid DNA irradiatedin vacuum

Citation
Km. Prise et al., Critical energies for SSB and DSB induction in plasmid DNA by low-energy photons: action spectra for strand-break induction in plasmid DNA irradiatedin vacuum, INT J RAD B, 76(7), 2000, pp. 881-890
Citations number
50
Categorie Soggetti
Experimental Biology
Journal title
INTERNATIONAL JOURNAL OF RADIATION BIOLOGY
ISSN journal
09553002 → ACNP
Volume
76
Issue
7
Year of publication
2000
Pages
881 - 890
Database
ISI
SICI code
0955-3002(200007)76:7<881:CEFSAD>2.0.ZU;2-B
Abstract
Purpose: To measure action spectra for the induction of single- strand brea ks (SSB) and double-strand breaks (DSB) in plasmid DNA by low-energy photon s and provide estimates for the energy dependence of strand-break formation important for track-structure simulations of DNA damage. Materials and methods: Plasmid pMSG-CAT was irradiated as a monolayer, unde r vacuum, with 7-150 eV photons produced by a synchrotron source. Yields of SSB and DSB were determined by the separation of the three plasmid forms b y gel electrophoresis. Results: The yields of SSB per incident photon increased from 1.4 x 10(-15) SSB per plasmid per photon/cm(2) at 7 eV to 7.5 x 10(-14) SSB per plasmid per photon/cm(2) at 150 eV. Direct induction of DSB was also detected incre asing from 3.4 x 10(-17) DSB per plasmid per photon/cm(2) at 7 eV to 4.1 x 10(-15) DSB per plasmid per photon/cm(2) at 150 eV. When the absorption cro ss-section of the DNA was considered, the quantum efficiency for break form ation increased over the energy range studied. Over the entire energy range , the ratio of SSB to DSB remained constant. Conclusions: These studies provide evidence for the ability of photons as l ow as 7 eV to induce both SSB and DSB. The common action spectrum for both lesions suggests that they derive from the same initial photoproducts under conditions where the DNA is irradiated in vacuum and a predominantly direc t effect is being observed. The spectral and dose-effect behaviour indicate s that DSB are induced predominantly by single-event processes in the energ y range covered.