Nuclei from murine lymphoma cells (L5178Y), labelled with 1.5 μCi14 C per mg DNA were digested with deoxyribonuclease I. The DNA which remained acid precipitable after various time intervals was found to have a lower specific radioactivity than the original material. The same behavior was observed when isolated radio-active DNA was enzymically digested, suggesting that the labeled DNA itself is more labile to nuclease action. It is considered unlikely that the effect is due to damage caused to the DNA by either the emergent β-particle or by recoil. Possibly the labeled DNA behaves as a modified substrate for the enzyme.

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