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

ABSTRACT: By studies in vivo with purified nuclei from rat liver, it was shown that a non-lethal dose of cycloheximide causes a decrease in the content of total nuclear ribonucleoprotein complexes by 2h 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 ribonucleoprotein content was not due to a decreased synthesis, but rather to an increased transport to the cytoplasm. The results of a double-radioisotope technique support the conclusion that, during the inhibitory phase of protein synthesis brough on by cycloheximdie, gene transcription continues and the gene product is transported to the cytoplasm for subsequent translation.

SUBMITTER: Ch'ih JJ

PROVIDER: S-EPMC1186565 | biostudies-other | 1979 Mar

REPOSITORIES: biostudies-other

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Project description:Annulate lamellae are cytoplasmic organelles containing stacked sheets of membranes embedded with pore complexes. These cytoplasmic pore complexes at annulate lamellae are morphologically similar to nuclear pore complexes at the nuclear envelope. Although annulate lamellae has been observed in nearly all types of cells, their biological functions are still largely unknown. Here we show that SUMO1-modification of the Ran GTPase-activating protein RanGAP1 not only target RanGAP1 to its known sites at nuclear pore complexes but also to annulate lamellae pore complexes through interactions with the Ran-binding protein RanBP2 and the SUMO-conjugating enzyme Ubc9 in mammalian cells. Furthermore, upregulation of annulate lamellae, which decreases the number of nuclear pore complexes and concurrently increases that of annulate lamellae pore complexes, causes a redistribution of nuclear transport receptors including importin ?/? and the exportin CRM1 from nuclear pore complexes to annulate lamellae pore complexes and also reduces the rates of nuclear import and export. Moreover, our results reveal that importin ?/?-mediated import complexes initially accumulate at annulate lamellae pore complexes upon the activation of nuclear import and subsequently disassociate for nuclear import through nuclear pore complexes in cells with upregulation of annulate lamellae. Lastly, CRM1-mediated export complexes are concentrated at both nuclear pore complexes and annulate lamellae pore complexes when the disassembly of these export complexes is inhibited by transient expression of a Ran GTPase mutant arrested in its GTP-bound form, suggesting that RanGAP1/RanBP2-activated RanGTP hydrolysis at these pore complexes is required for the dissociation of the export complexes. Hence, our findings provide a foundation for further investigation of how upregulation of annulate lamellae decreases the rates of nuclear transport and also for elucidation of the biological significance of the interaction between annulate lamellae pore complexes and nuclear transport complexes in mammalian cells.

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

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