Effects of Cycloheximide upon Formation of Ribonucleic Acid Cytidylic and Uridylic Acids

Concentrations of cycloheximide as low as 3 mug/ml inhibited incorporation of labeled orotic acid or uridine into RNA cytidylic acid of soybean (Glycine max) hypocotyl sections. Even lower concentrations of this well known protein synthesis inhibitor interfered with conversion of labeled cytidine into RNA uridylic acid. Both cycloheximide and puromycin inhibited absorption of (3)H-phenylalanine and its incorporation into protein, but puromycin did not significantly affect the labeling patterns of RNA cytidylic and uridylic acids when orotic acid-6-(14)C was fed. Results give further support to the hypothesis that cycloheximide inhibits the interconversion of uridine and cytidine nucleotides, presumably by acting as a glutamine antagonist in the glutamine-dependent reaction catalyzed by cytidine triphosphate synthetase.