title: Evaluation of lesion clustering in irradiated plasmid DNA.
abstract: OBJECTIVE
  To measure the yield of DNA strand breaks and clustered lesions in plasmid DNA irradiated with protons, helium nuclei, and y-rays.
  
  
  METHODS
  Plasmid DNA was irradiated with 1.03, 19.3 and 249 MeV protons (linear energy transfer = 25.5, 2.7, and 0.39 keV microm(-1) respectively), 26 MeV helium nuclei (25.5 keV microm) and gamma-rays (137Cs or 60Co) in phosphate buffer containing 2 mM or 200 mM glycerol. Single-and double-strand breaks (SSB and DSB) were measured by gel electrophoresis, and clustered lesions containing base lesions were quantified by converting them into irreparable DSB in transformed bacteria.
  
  
  RESULTS
  For protons, SSB yield decreased with increasing LET (linear energy transfer). The yield of DSB and all clustered lesions seemed to reach a minimum around 3 keV microm(-1). There was a higher yield of SSB, DSB and total clustered lesions for protons compared to helium nuclei at 25.5 keV microm(-1). A difference in the yields between 137Cs and 60Co gamma-rays was also observed, especially for SSB.
  
  
  CONCLUSIONS
  In this work we have demonstrated the complex LET dependence of clustered-lesion yields, governed by interplay of the radical recombination and change in track structure. As expected, there was also a significant difference in clustered lesion yields between various radiation fields, having the same or similar LET values, but differing in nanometric track structure.
authors.affiliation: Dept. of Particle Physics, Weizmann Institute of Science, Rehovot 76100, Israel. cl2235@columbia.edu
authors.forename: C
authors.initials: C
authors.lastname: Leloup
authors.forename: G
authors.initials: G
authors.lastname: Garty
authors.forename: G
authors.initials: G
authors.lastname: Assaf
authors.forename: A
authors.initials: A
authors.lastname: Cristovão
authors.forename: A
authors.initials: A
authors.lastname: Breskin
authors.forename: R
authors.initials: R
authors.lastname: Chechik
authors.forename: S
authors.initials: S
authors.lastname: Shchemelinin
authors.forename: T
authors.initials: T
authors.lastname: Paz-Elizur
authors.forename: Z
authors.initials: Z
authors.lastname: Livneh
authors.forename: R W
authors.initials: RW
authors.lastname: Schulte
authors.forename: V
authors.initials: V
authors.lastname: Bashkirov
authors.forename: J R
authors.initials: JR
authors.lastname: Milligan
authors.forename: B
authors.initials: B
authors.lastname: Grosswendt
mesh_terms: D000512:Alpha Particles / Q000009:adverse effects*; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004269:DNA, Bacterial; D005720:Gamma Rays / Q000009:adverse effects*; D018499:Linear Energy Transfer / Q000528:radiation effects; D008954:Models, Biological; D010957:Plasmids / Q000528:radiation effects; D011522:Protons / Q000009:adverse effects*; D011832:Radiation Injuries / Q000209:etiology*
chemical_list: D004269:DNA, Bacterial; D011522:Protons; D004247:DNA