Abstract
DNA fragments of defined sequence were used to study DNA strand breakage by gamma radiation in doses ranging from 2,500 to 20,000 rads. The amount of radiation-induced DNA breakage is linearly dose-dependent, and strand scission events occur uniformly at all nucleotide sites, regardless of sequence. The 5'-terminal group at points of breakage is a simple phosphoryl moiety. Two types of radiation-induced 3' termini were identified. One species of 3' terminus is a simple phosphoryl group. The other species of 3' terminus is neither a hydroxyl nor a phosphoryl group. A model for radiation-induced DNA strand scission that involves destruction of the deoxyribose moiety is presented. Similarities among DNA strand scission events created by gamma radiation, ferrous ion, doxorubicin, and bleomycin are discussed.
Highlights
DNA fragmentsofdefinedsequencewere used to within the strand and the relationship of sugar-phosphate study DNA strandbreakageby y radiation in doses damage to specific base sites has not been studied
Sites of Strand Scission by y Radiation-To investigate the sites of strand scission in DNA created by y radiation, DNA fragments 150 nucleotides long labeled at the3’ terminus were exposed to radiation from a cobalt40 source in a dose range from 0 to 15,000 rads
The experiments presented here demonstrate that y radiation creates, under theseconditions, single strand breaks at all nucleotide sites in a DNA molecule with equal probability, regardless of nucleotide sequence
Summary
DNA fragmentsofdefinedsequencewere used to within the strand and the relationship of sugar-phosphate study DNA strandbreakageby y radiation in doses damage to specific base sites has not been studied. Removal conditions of ambient temperature and atmospherTe.o deter- of a phosphoryl group from the 5’ end of a scission product mine if the scission products of the ferrous ion reaction were decreases the charge/mass ratioof the DNA and results in a identical with thoseproduced by y radiation, a 150-nucleotide decreased electrophoretic mobility of the product [15]. Scission products produced by treatment of the same 5' end-labeled DNA with the sequencing reagents of Maxam and Gilbert [10]were compared on adjacent lanesof the same gel (Fig. 4).
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