| Abstract: | The application of an external electric field simultaneously with gamma irradiation to an aqueous suspension of phi X174 DNA (in the RFI form) is shown to increase significantly the number of strand breaks. Tritiated DNA allowed the number of single-strand breaks to be estimated from changes in the scintillation of electrophoretic gel band associated with the fastest mobility moiety. At 400 V (approximately 2400 V cm-1) the corrected increase (corrected for phoresis of DNA on the stainless-steel plates) in the G-value yield is 38%. The increase in damage with field strength appears to follow the increase in reduced dichroism. Dichroism results correspond at 400 V to approximately 10% of the maximum orientation. Our results support the conjecture that this significant increase in DNA-radiation interaction with an electric field is due to field-induced conformation changes in the molecule. |
