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Studies on the Mechanism of Template Stability: Cytoplasmic DNA-like RNA in Hepatocellular Carcinomas¹

Departments of Oncology and Pathology, McArdle Laboratory for Cancer Research, The Medical School, University of Wisconsin, Madison, Wisconsin 53706

Administration of actinomycin D to rats that have received inorganic ³²PO₄ to label their RNA results in a marked decrease in the total labeling of cytoplasmic RNA within a 3-hr period. However, the ³²P-labeled nucleotide composition of the RNA labeled in the presence of actinomycin D in vivo is quite similar to that of rat liver DNA, rather than to ribosomal RNA. The studies described in this paper demonstrate that this DNA-like RNA is associated with both the rough endoplasmic reticulum and the free polysomes of liver. It is also present in both the rough endoplasmic reticulum and the free polysomes of the Morris hepatomas 5123c and 7800, as well as the Reuber hepatoma H-35. The possibility that this DNA-like RNA may be associated with or equal to the postulated stable RNA templates in liver and hepatoma cytoplasm is discussed.

¹ This investigation was supported in part by National Cancer Institute Grant CA-07175 and the American Cancer Society Grant P-314.

² Postdoctoral Trainee in Cancer Research of the National Cancer Institute. Present address: Department of Pharmacology, University of Minnesota, Minneapolis, Minn. 55455.

Received 9/ 8/69. Accepted 1/26/70.