Abstract
The intracellular distribution and activity of enzymes which act on DNA in oocytes of Xenopus laevis have been investigated by injecting conformational variants of SV40 DNA into the oocyte's nucleus or cytoplasm. Single-stranded DNA and linear double-stranded DNA were degraded by both nucleus and cytoplasm. Circular double-stranded DNA was degraded after injection into the cytoplasm but was conserved and assembled into chromatin after injection into the nucleus. Nicked circular DNA was efficiently ligated in the nucleus. Chromatin assembly in the nucleus is extraordinarily active. Each oocyte can convert a mass of DNA equivalent to 1000 diploid Xenopus laevis nuclei to a nucleoprotein complex resembling naturally occurring SV40 minichromosome in its sedimentation, buoyant density, superhelicity, localized nuclease sensitivity, and beaded appearance under an electron microscope. This nucleoprotein complex, containing covalently closed circular DNA, was the only stable DNA form detected. Comparison with previous reports shows that efficient transcription of SV40 DNA injected into oocytes occurs only under circumstances in which the nucleoprotein complex is formed.
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