The Occurrence of Double-strand Breaks in Coliphage T1-DNA by Iodine-125 Decay

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Abstract
DNA of Coliphage T1 was labelled with 125I-iododeoxyuridine. Inactivation of plaque forming ability and sedimentation behaviour of DNA was studied during the radioactive decay of 125I. The absence of a temperature effect as well as the observation that a radical scavenger does not influence inactivation supports the view that ionizing radiation is not responsible for loss of phage viability. However, experimental evidence is given for DNA double-strand breaks being the relevant lethal event caused by electron vacancy cascades (Auger effect). The ratio of single- to double-strand breaks was calculated to be 1·1 : 1. The relationship of 1 : 1 was found between the numbers of lethal events and of double-strand breaks.