Reversible inhibition of ribosomal RNA synthesis in HeLa by lucanthone (Miracil D) with continued synthesis of DNA‐like RNA

Ribosomal RNA synthesis was selectively inhibited in HeLa cells by lucanthone, a clinically useful schistosomicide which shares many of the properties of Actinomycin D. Synthesis of DNA‐like RNA continued during complete inhibition of ribosomal RNA synthesis. Under these conditions newly synthesized DNA‐like RNA accumulated normally in polyribosomes of the cell cytoplasm; most of it appeared to be messenger RNA. DNA synthesis was partially inhibited by lucanthone but protein synthesis was undisturbed. Synthesis of ribosomal RNA promptly resumed after removal of lucanthone and cell survival was not affected if exposures to the drug were limited to two hours.