Comparison of the Oxygen-enhancement Ratio for γ-ray-induced Double-strand Breaks in the DNA of Bacteriophage T7 as Determined by Two Different Methods of Analysis

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Abstract
Bacteriophage T7 was irradiated in a protecting medium under nitrogen and oxygen with 60Co gamma-rays. Double-strand breaks were measured by sucrose-gradient sedimentation and by boundary-sedimentation analysis. Both methods showed that the presence of oxygen during irradiation enhanced the production of double-strand breaks. This is at variance with a recent report which suggests that boundary-sedimentation analysis does not show an effect of oxygen. The discrepancy must be ascribed to differences in interpretation of the sedimentation data.