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On the Mechanism of Radiosensitization by 5-Bromouradl.The Occ u r r enc e of DNA Strand Breaks in UV -Irradiated Phage T4 as Influenced by Cysteamine G. Hotz , R. Walser Photochemistry and Photobiology. 1970. Vol.12, pp. 207-218 Abstract-U.V.-irradiation of phage T4Bo" resuits in a decrease in sedimentation rate of BU-DNA which is attributed to single-and double-strand breaks. No breaks could be observed in unsubstituted DNA. Cysteamine present during u.v.-irradiation is able to prevent doublestrand breaks but does not influence the production of single-strand breaks rneasured by alkaline sucrose gradient centrifugation. The biological importance and nature of DNA strand breaks due to BU-incorporation as weIl as the action of the protective agent on these breaks and on the biological activity are discussed.

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