HUMAN LEUKEMIC CELLS . ACTINOMYCIN D-RESISTANT BIOSYNTHESIS OF RNA BY ISOLATED NUCLEI

Nuclei isolated from human (CCRF-CEM) leukemic cells are metabolically active, as evidenced by precursor incorporation studies. Although 0.1 γ/ml of actinomycin D completely inhibits the growth of CCRF-CEM cells, this concentration had little or no effect on the metabolic activity of isolated nuclei, as adjudged by the incorporation of labeled thymidine, uridine, and lysine. However, higher concentrations (0.25 γ-0.5 γ/ml) of actinomycin D inhibited DNA synthesis, but did not effectively inhibit RNA and protein syntheses. The present experiments suggest that there may be an RNA-replicating system in the CCRF-CEM nuclei which is resistant to inhibition by actinomycin D. The precise nature of this system remains to be determined. © 1969.