Analysis of gamma radiation-induced damage to plasmid DNA using dynamic size-sieving capillary electrophoresis

Bacterial plasmids and the chromosomal DNA of many organisms adopt naturally the negatively supercoiled conformation. Therefore, the irradiation of such plasmids could be used to model conformational changes of chromosomal DNA associated with externally-induced damage. We have applied dynamic size-sieving capillary electrophoresis (CE) to monitor the damage of three DNA plasmids, over an unprecedented base pair (bp) size range (2870-27 500 bp), upon exposure to gamma-radiation (20-400 Gy). Predominantly, CE with UV absorbance detection in the absence of DNA intercalating dyes was employed to preclude undesirable, induced plasmid conformational changes. Plasmid samples and their enzymatic digestion products were analyzed using both CE and slab gel electrophoresis (SGE) in order to verify the conformation of sample components. Relative to SGE, CE analyses revealed more fine structural features of plasmid degradation.