The Influence of Oxygen and Sulphhydryl Compounds on the Production of Breaks in Bacteriophage DNA by Gamma-rays

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Abstract
After irradiation of T4 or T7 bacteriophage with γ-rays, the DNA was isolated and analysed for double- and single-strand breaks by sedimentation in a sucrose gradient. In the absence of oxygen, the number of double-strand breaks per krad and per molecular weight of 109 daltons is 0·04. In the presence of oxygen it is 0·08. The yield of single-strand breaks is 10 to 20 times higher than that of double-strand breaks. It is shown that in bacteriophage the increase of the production of DNA breaks by oxygen does not manifest itself as an increased sensitivity of the bacteriophage as a whole, because the presence of oxygen prevents other types of damage, presumably in the protein coat. If sulphhydryl compounds are present the yield of breaks is not much affected, but the amount of other damage is considerably reduced. A normal oxygen effect is then observed.