DEOXYRIBONUCLEIC ACID LABELLING AFTER TRITIATED THYMIDINE INJECTION

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Abstract
Young rats were injected with thymidine-3H and the level of radioactivity in their blood was measured by a highly sensitive radioautographic technique. Radioactivity (10−6 μcurie/ml) was still detected in serum 7 days after injection. To determine whether the blood of these rats contained deoxyribonucleic acid (DNA) precursors, the sera, taken at various time intervals after injection, were introduced into tissue culture chambers. By radioautography of these cultures, it was found that they contained cells with labelled nuclei, even when exposed to sera taken 30 hours after injection. The presence of nuclear precursors in these sera probably indicates a reutilization of DNA from other cells.