Selective inhibition of ribosomal RNA synthesis in Ehrlich ascites tumor cells by a non-specific inhibitor, 2,4-dinitrophenol

Abstract

The incorporation of [ 32P]phosphate into the RNA of Ehrlich ascites tumor cells in vitro, in the presence of actinomycin D or 2,4-dinitrophenol, was investigated. 1. 1. The RNA labelled in vitro for 2 and 5 h forms two broad peaks which have electrophoretic mobilities on agar gel corresponding to about 45-S and 32-S RNA. The nucleotide composition of the 32P-labelled RNA gives a G+C A+U ratio of 1.30–1.38. These characteristics indicate that the precursors of rRNA are synthesized in vitro under the specified experimental conditions. 2. 2. Incubation of tumor cells with 0.1–0.5 mM 2,4-dinitrophenol brings about an 80–90% inhibition of overall RNA synthesis. A similar inhibition of RNA synthesis is observed in the presence of 1 μg/ml of actinomycin D. The RNA labelled in the presence of either 2,4-dinitrophenol or actinomycin D displays a heterogeneous distribution (in the zone 10–30 S) and complete disappearance of the label in the zone of rRNA precursors. The RNA labelled in the presence of both inhibitors shows a G+C A+U ratio of 1.02–1.10. These results show that both actinomycin D and 2,4-dinitrophenol cause a preferential inhibition of rRNA synthesis.