Regulation of mammalian protein synthesis in vivo. Simulated transport of nuclear ribonucleoprotein complexes to the cytoplasm after cycloheximide treatment

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Abstract
In vivo studies with purified nuclei from rat liver showed that a non-lethal dose of cycloheximide causes a decrease in the content of total nuclear ribonucleoprotein (RNP) complexes by 2 h after treatment. Analysis of the complex by sucrose-density-gradient centrifugation substantiated this observation for the faster-sedimenting complex, but showed an increase in the content of a smaller complex. Radioisotope incorporation studies showed that the overall decrease in nuclear RNP content was due not to a decreased synthesis but to an increased transport to the cytoplasm. The results of a double-radioisotope technique suggest that, during the inhibitory phase of protein synthesis brought on by cycloheximide, gene transcription continues and the gene product is transported to the cytoplasm for subsequent translation.