Evidence that free polysomes are not the precursors of membrane-bound polysomes in rat liver
| Autor: | Boyd A. Howell, David P. Ringer, Bettye Cox, Joseph A. Clouse, Donald E. Kizer |
|---|---|
| Rok vydání: | 1982 |
| Předmět: |
Cytoplasm
Orotic acid Protein subunit Biophysics Biology Endoplasmic Reticulum Biochemistry Ribosome chemistry.chemical_compound Structural Biology Polysome Genetics medicine Animals HEPES Translation (biology) Intracellular Membranes Compartment (chemistry) Ribosomal RNA Cell Compartmentation Rats chemistry RNA Ribosomal Polyribosomes Microsomes Liver Female Ribosomes medicine.drug |
| Zdroj: | Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression. 697:353-362 |
| ISSN: | 0167-4781 |
| DOI: | 10.1016/0167-4781(82)90099-9 |
| Popis: | We tested, in rat liver, the postulate that free polysomes were precursors of membrane-bound polysomes. Three methods were used to isolate free and membrane-bound ribosomes from either post-nuclear or post-mitochondrial supernatants of rat liver. Isolation and quantitation of 28 S and 18 S rRNA allowed determination of the 40 S and 60 S subunit composition of free and membrane-bound ribosomal populations, while pulse labeling of 28 S and 18 S rRNA with [6- 14 C]orotic acid and inorganic [ 32 P]phosphate allowed assessment of relative rates of subunit renewal. Throughout the extra-nuclear compartment, 40 S and 60 S subunits were present in essentially equal numbers, but, free ribosomes contained a stoichiometric excess of 40 S subunits, while membrane-bound ribosomes contained a complementary excess of 60 S subunits. Experiments with labeled precursors showed that throughout the extra-nuclear compartment, 40 S and 60 S subunits accumulated isotopes at essentially equal rates, however, free ribosomes accumulated isotopes faster than membrane-bound ribosomes. Among free ribosomes or polysomes, 40 S subunits accumulated isotopes faster than 60 S subunits, but, this relationship was not seen among membrane-bound ribosomes. Here, 40 S subunits accumulated isotope more slowly than 60 S subunits. This distribution of labeled precursors does not support the postulate that free polysomes are precursors of membrane-bound polysomes, but, these data suggest that membrane-bound polysomes could be precursors of free polysomes. |
| Databáze: | OpenAIRE |
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