Effect of ethidium bromide intercalation on DNA radiosensitivity.
OBJECTIVE
To assess the influence of the intercalating drug ethidium bromide (EtBr) on the yields of single strand breaks (ssb) induced by fast neutrons in supercoiled pBR322 plasmid and in a linear DNA restriction fragment.


METHODS
The yield of ssb in the plasmid was measured by agarose gel electrophoresis. The proportion of fragments bearing one ssb and the probability of breakage at each nucleotide site was determined using sequencing gel electrophoresis. The volume variations due to the intercalation of EtBr were calculated. The expected radio-modifying effect at each nucleotide site of the linear fragment was evaluated using a reported simulation procedure.


RESULTS
The ssb yield in the plasmid increased for concentrations up to 0.04 drug/bp and fell back in the range 0.04-0.1 drug/bp. For the linear DNA, only a slight protective effect was observed over the whole concentration range. The effect was almost the same at all nucleotide sites.


CONCLUSIONS
For the linear DNA fragment, radioprotection was mainly due to scavenging of OH* radicals by the intercalated drug. For the plasmid, the radio-modifying effect results mainly from the variation of its effective volume, due to the modification of superhelicity.
Begusová
M
M
Centre de Biophysique Moléculaire, CNRS, Orléans, France.
Spotheim-Maurizot
M
M
Michalik
V
V
Charlier
M
M
D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004278:DNA, Superhelical / Q000528:radiation effects; D004587:Electrophoresis, Agar Gel; D004926:Escherichia coli / Q000235:genetics; D004996:Ethidium / Q000494:pharmacology*; D005214:Fast Neutrons; D016166:Free Radical Scavengers / Q000378:metabolism; D017665:Hydroxyl Radical / Q000737:chemistry; D007364:Intercalating Agents / Q000494:pharmacology*; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000528:radiation effects; D011836:Radiation Tolerance / Q000187:drug effects; D011837:Radiation-Protective Agents / Q000494:pharmacology
D004278:DNA, Superhelical; D016166:Free Radical Scavengers; D007364:Intercalating Agents; D011837:Radiation-Protective Agents; D017665:Hydroxyl Radical; D004247:DNA; D004996:Ethidium