Strand breaks in native DNA 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 hr in 0.1 N NaOH (G values are 0.58 at pH 5.4 and 1.47 at pH 12.4 for 0.12 percent DNA; 1.0 at pH 4.0-6.8 and 2.43 at pH 12.4 for 0.21 percent DNA). The half-life of alkaline-induced monophosphate termini was 4.1 hr, similar to that for alkaline hydrolysis of apurinic sites in DNA.
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Kay et al. (1977) studied this question.