Incorporation of tritiated thymidine into deoxyribonucleic acid by isolated nuclei

Cytoplasmic control of nuclear DNA synthesis during early development of Xenopus laevis: a cell-free assay

Nuclei isolated from nondividing cells were induced to synthesize DNA by incubation with cytoplasm from early embryos of Xenopus laevis. Numerous replication eyes were formed in the nuclear DNA molecules, and high levels of [3-H]dTTP were incorporated. With this assay a protein(s) which appears to initiate DNA synthesis was found at high levels in the cytoplasm of eggs, blastulae, or gastrulae, but only at low levels in the cytoplasm of oocytes, hatched embryos, or adult tissues.

Macromolecular content of inclusions produced by a canine adenovirus

Early inclusions induced by a canine adenovirus in a canine cell line, appearing before the formation of infectious virus particles, were purified by differential centrifugation in sucrose followed by CsCl density gradient centrifugation. Chemical analysis of these inclusions revealed that they contained deoxyribonucleic acid (DNA), ribonucleic acid, and protein. On the basis of density gradient centrifugation, the DNA extracted from the inclusions was found to be viral DNA. Electron microscope autoradiography showed that these inclusions were the sites of DNA synthesis. In addition, association of DNA polymerase activity with the inclusions was detected by incorporation of radioactivity from (3)H-thymidine triphosphate into a DNA product. The in vitro product of the enzyme had a density equal to that of viral DNA rather than host DNA. The level of DNA polymerase activity in exponentially growing infected and uninfected whole cells was similar, but in cells in stationary phase the enzyme activity of infected cells was twice that in noninfected cells. Furthermore, nuclei isolated from infected cells showed a fourfold increase in DNA polymerase activity over the noninfected cells.