Strand Breaks in X-Irradiated Crystalline DNA: Alternating CG Oligomers

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Direct ionization of crystalline d(CGCGCGCG) and d(CGCGCGCGCG) oligomers produces 3′- and 5′-phosphate-terminated fragments as the main strand breakage products detectable by ion-exchange chromatography. The nature of the base has no effect on the probability of strand breakage at the given site. The yields of 3′-phosphates are systematically lower than the yields of the 5′-phosphates originating from the same cleavage site, pointing to the possible presence of unidentified products with sugar remnants attached to the 3′-end. These results show that direct ionization is efficient at producing single-strand breaks in DNA and its action is relatively indiscriminate with respect to base sequence.