EFFECT OF EHRLICH ASCITES CELL CHALONE ON NASCENT DNA SYNTHESIS IN ISOLATED NUCLEI |
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| Authors: | G S Nakai Hella Gergely |
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| Institution: | Medical &Research Services, Veterans Administration Hospital, Long Beach, California, and Department of Medicine, University of California School of Medicine, Irvine, California, U.S.A. |
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| Abstract: | Ehrlich Ascites Tumor (EAT) chalone has been shown to inhibit nascent DNA synthesis by inhibiting DNA polymerase α and β (Nakai, 1976), but one of the problems in studying eurkaryotic DNA replication has been the relative impermeability of the cell membrane to precursors and macromolecules; hence, to circumvent this restriction without sacrificing the integrity of the replication process, a broken cell system utilizing nuclei in aqueous media was investigated. Isolated nuclei appear to continue the process of DNA replication that was proceeding in vivo before their isolation and under optimal conditions are able to initiate new synthesis (Fraser & Huberman, 1977). The effects of partially purified EAT chalone on nascent DNA could be studied directly in this nuclear system, which excluded effects of the cell membrane, nucleotide pools and other cytosol elements. A concentration-related inhibition of 3H]thymidine triphosphate (3H]-dTTP) incorporation was noted over a chalone range of 50–200 μg/ml. It appears that chalone can inhibit DNA polymerase α directly within the nucleus without an intermediate step such as a cell membrane receptor. |
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