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Physico Chemical Events

(MS012) Clustered DNA damages induced by high LET ionizing radiation in T7 DNA.

Hada, Megumi^{*,1, 2}, Sutherland, Betsy³, ¹ Division of Space Life Science, Houston, TX, USA² Radiation Biology, Houston, TX, USA³ Biology Department, Upton, NY, USA

ABSTRACT- Ionizing radiation induces clustered DNA damages in DNA—two or more abasic sites, oxidized bases and strand breaks on opposite DNA strands within a few helical turns. Clustered damages are considered to be more lethal and mutagenic damages. Although induction of single strand breaks and isolated lesions has been studied extensively, little is known of factors affecting induction of clusters other than double strand breaks (DSB). The aim of the present study was to determine whether the type of incident radiation could affect yield or spectra of specific clusters. T7 DNA, a double stranded 40 kp duplex, was irradiated in non-scavenging buffer conditions with Fe (970 MeV/n), Ti (980 MeV/n), C (293 MeV/n), Si (586 MeV/n) ions, or protons (1 GeV/n) at the NASA Space Radiation Laboratory or 100 kVp X-rays. Irradiated DNA was treated with homogeneous Fpg or Nfo proteins (or without enzyme treatment for DSB quantitation), then electrophoresed in neutral agarose gels. DSB, Fpg-OxyPurine clusters, and Nfo-Abasic clusters were quantified by number average length analysis. The results show that the yields of all these complex damages depend on the incident radiation. Further, the spectrum of damage also depends on the radiations. The yield (damage/Mbp/Gy) of all damages decreased with increasing linear energy transfer (LET) of the radiation. Further, the relative frequencies of DSBs relative to Abasic- and OxyBase clusters were lower for ionizing photons than for charged particles. The relative levels of OxyPurine clusters to Abasic clusters may increase with increasing LET. The work was supported by DOE, NASA and NIH.

Key words: Clustered DNA damage, High LET ionizing radiation, Double strand breaks, T7 DNA