Covalently closed circular DNA from polyoma virus (component I) was injected into enucleated unfertilized eggs of Xenopus laevis together with [3H]thymidine. Polyoma DNA stimulated [3H]thymidine incorporation and part of the labelled product had the sedimentation characteristics of component I polyoma DNA. Polyoma component I DNA was prepared with a density label (5‐bromo deoxyuridine) in one strand and tritium in the other. After injection into egg cytoplasm, part of the labelled material changed buoyant density to that of normal (light) double‐stranded polyoma DNA, indicating the synthesis of new DNA strands rather than terminal addition or partial strand repair. 14C‐labelled component I polyoma DNA of hybrid buoyant density was prepared and injected together with [3H]thymidine. Part of the newly synthesized material was complementary to, and hydrogen bonded to, the heavy parental strands. Degradation of the injected DNA could not be detected suggesting that the strand synthesis observed was due to replication of the injected DNA rather than nick translation.
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Laskey et al. (1973) studied this question.
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