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The restitution of RNA synthesis in cultures progressing from metaphase into interphase (G I ) has been investigated in synchronized HeLa S 3 cells by using inhibitors of macromolecular synthesis and the technique of electron microscope autoradiography . The rate of incorporation of radioactive uridine into RNA approached interphase levels in the absenceofrenewed protein synthesis . In contrast, maintenance of this rate in G I was dependent upon renewed protein synthesis . Restoration of synthesis of heterogeneous nuclear RNA occurred under conditions that inhibited production of ribosomal precursor RNA . In autoradiographs of individual cells exposed to radioactive uridine, silver grains were first detected after nuclear envelope reformation at the periphery of the chromosome mass but before chromosomal decondensation . These data are consistent with the following interpretation . Multiple RNA polymerase activities persist through mitosis and are involved in the initiation of RNA synthesis in early telophase at sites on the nuclear envelope .

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Aspects of the ingestion and early intracellular fate of homologous. [3H]-thymidine-labeled chromosomes (donor) were studied in recipient Wi-L2 cells in the absence of reutilized radioactivity. As much as 67% of the cell-associated radioactivity was resistant to hydrolysis by DNase I after 4 h of incubation. Cell fractionation and electron microscope autoradiography indicated that chromosome uptake was rapid, into both cytoplasmic and nuclear fractions and was facilitator and dose dependent. Sedimentation analysis demonstrated that at 4 h donor DNA of approximate single-strand mol wt of 1--6 X 10(6), as compared to 6--12 X 10(6) for chromosomal DNA, was recoverable in cell fractions. By 6 h, a significant portion of the nucleus-associated donor DNA was converted into material of higher mol wt, although no evidence was found for integration into recipient DNA. Cytoplasmic donor DNA continued to be degraded. An average number of chromosome equivalents of nucleus-associated donor DNA to recipient cell nuclei of 1--4 was obtained and its relationship to the lower frequency of chromosome-mediated gene transfer is discussed.