Studies on a Bromouracil-Labelled DNA Fraction Induced by Antigenic Stimulation.

When primed guinea-pig lymph-node cells are incubated in vitro with homologous antigen and 5-bromo-2-deoxy-[³H]uridine, a peak of intermediate density appears between hybrid and normal DNA. This peak does not result from the attachment of a low density substance to DNA, since it is still present in denaturation conditions or after extensive digestion by pronase or phospholipase. By contrast, it disappears after DNA breakage by sonication, indicating that it results from end-to-end joining of labelled and unlabelled DNA segments. [ABSTRACT FROM AUTHOR]