Study on Plasmid DNA Damage Induced by Low energy Neon Ion Irradiation

Key words: 
• heavy ions /
• DNA doublestrand break /
• nonrandom distribution /
• plasmid DNA

Abstract: DNA is considered to be the most important and sensitive target in biological systems. In addition to the base damage, DNA strand breaks are the major lesion in the genome due to exposure to ionizing radiation. Mutation can be introduced to DNA as a result of enzymatic processing of DNA lesions or postirradiation replication. However, the mechanisms of radiationinduced mutations are not well clarified at the molecular level. To study the effect on the simple plasmid DNA of heavy ion is even predominant or more feasible. 
Plasmid pUC18 DNA was prepared and irradiated by neon beam (7.199 MeV/u). The fragment distributions were determined by quantifying the ethidium bromide fluorescence. It can be seen that the shape of the intensity distributions is vastly different for the used radiation Dose. The distribution produced shows an excess of fragments particularly in 3 000 and 10 000 Gy the size range between 20—40 kbp and 20—50 bp. This clustering of doublestranded fragments might be influenced by the higher order chromatin structure of genomic DNA. If so, DNA loop structures could correspond to the size range for which we observed DSB clustering. Further studies aim at elucidating the heterogeneity of DSB induction within the genome and investigate the influence of chromatin structure on the nonrandom fragment distribution.