Distribution Of Fragmentations Of Radiation Induced DNA Double-strand Breaks

Objective: The purpose of the research is to study the mechanism of DNA double- strand breaks (DSB) by determining the yields and the distribution of DSB induced by ⁶⁰Co γ ray, and exploring the condition of the statistical fragmentation model based in comparison of the experimental data.Methods: The research was divided into two parts. 1. Normal human fibroblast cells GM0639 were irradiated by Gamma ray emitted from source ⁶⁰Co. The yields and distribution of double- strand breaks (DSB) were measured by the method of pulsed-field gel electrophoresis (PFGE) by subtracting the contributions of the background. 2. The formula of the statistical fragmentation model was established to analyze the contributions of linear and exponential function based on the experimental data with the model.Results: The results showed that the fractions of the activity released (FAR) of GM0639 cell's DNA fragmentations increased from 55% to 85% as the dose increased from 20 to 100Gy and reached to a threshold (～85% ) at higher doses. The mean sizes of DNA fragments decreased from 1.35Mbp to 0.98Mbp as the dose increased. When plotted the breakage levels with the doses, a yield of DSB of GM0639: (0.600 ± 0.06) × 10^-9Dsb/Bp/Gy was obtained. The distribution pattern of the fragments was derived under the condition in which the entropy was at maximum. With the approximation E ≈ E₀ + E₁l + E₂l², the distribution functions were resulted as exp(αl + βl²).Conclusions: 1. PFGE is a sensitive method in analyzing fragmentations of DNA double strand breaks. 2. With the increase of dose of γ-ray, the FAR of DNAincreases and the mean sizes of DNA fragments decrease respectively. 3. The experimental data support the radiation-induced DNA DSB statistical fragmentation model.