A study of DNA spontaneous degradation

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The intact apurinic site half-life in DNA molecules, at 37° C and pH 7.21, in a medium approximating the intracellular ionic composition, was found to be between 288 and 335 h. The spontaneous degradation of 3H-labelled T7 phage DNA, at 37° C and pH 7.21, in the same medium, was followed by sedimentation analysis on sucrose gradients after denaturation with NaOH; it was found to be equivalent to 0.009 break per h per DNA strand. The number of intact apurinic sites found in this incubated T7 phage DNA was much lower than the theoretical value calculated on the assumption that depurination was the only cause of DNA degradation. We concluded that depurination was a minor cause of DNA degradation in our experimental conditions.