Monophosphate End Groups Produced in Radiation-Induced Strand Breakage in DNA

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Abstract
Strand breaks in native DNA [calf thymus] irradiated in aqueous oxygenated solution were assayed in the form of monophosphate termini using acid phosphatase. A marked concentration effect on the yield (G value) of monophosphate end groups was observed. The effect of postirradiation alkali treatment showed a 2.5-fold increase in yield after 24 h in 0.1 N NaOH (G values are 0.58 at pH 5.4 and 1.47 at pH 12.4 for 0.12% DNA; 1.0 at pH 4.0-6.8 and 2.43 at pH 12.4 for 0.21% DNA). The half-life of alkaline-induced monophosphate termini was 4.1 h, similar to that for alkaline hydrolysis of apurinic sites in DNA.