Quantitative assessment of DNA damage accompanied with no substantial loss in its molecular weight during exposure to oxidative stress

摘要

A pUC 19 plasmid DNA(2.7 kbp)was injured under the oxidative stress generated from TiO_2 illuminated at incident light intensities of 9 and 16W/m~2.ThedegreeofDNAdamage(D/D_0)duringthephotoreactionwaswellexpressedbyamodelequation,D/D_0=1-[1 - exp(-theta)]~(P_0),where D_0 and D are DNA densities at an original position estimated by agarose gel electrophoresis at an onset and a given time of photoreaction,respectively,and 9 is overall dose of oxidative stress to DNA.The parameter(P_0)in this equation was determined to be P_0=15.1 for the pUC 19 plasmid irrespective of the examined light intensities.It was found that the P_0 value depended on DNA molecular size,giving P_0=10.3 in the case of a modified pUC 19 plasmid with an insertion of bacterial 16S rDNA(4.2 kbp).To estimate the degree of DNA damage in the absence of substantial loss in its molecular weight,the P value was defined as a remaining potential of DNA endurance against the oxidative stress,being formulated as P/P_0=exp(-theta).Transformation experiments were conducted by introducing the pUC 19 plasmid DNA injured by the oxidative stress into Escherichia coli,and it was found that the calculated value of P/P_0 could follow satisfactorily the experimental results showing a gradual decrease in the transformation efficiency with increasing theta value in a region of 0 < theta <=1.5.