ISSN:
1432-0878
Keywords:
Ribosomes
;
Polyribosomes
;
Messenger RNA
;
Protein synthesis
;
Cytoplasmic filaments
;
Cytoplasmic RNP-network
;
Electron microscopy
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary The ultrastructural morphology of ribosomes was studied in tissue sections of rat uterus using different fixatives (acrolein, formaldehyde, acetic acid, methanol-acetic acid, OsO4) after various pre-incubations in solutions of different osmolarity, electrolyte content, and pH. In addition, whole-mount ribosomes of spread cytoplasm of epithelial cells were examined. The results indicate: Ribosomes are “thickenings” in the course of a cytoplasmic RNP-network which extends in three dimensions between nucleus and plasma membranes. This network consists of fibrils which vary in width depending on intrinsic and extrinsic factors. Often the fibril width is approx. 100 Å. In places where the fibril is folded up into ribosomal “granules” and strands the width may be 300 Å. Each fibril seems to be composed of two elementary filaments, 10 Å up to 40 Å thick. Estimation of filament length within a ribosomal “granule” allowed the conclusion that only a fraction of a 45 S-RNA filament is folded up into a “ribosome” in cytological preparations. No morphological evidence was found for clefts within ribosomes or single messenger RNA filaments “piercing” ribosomes. Filaments of membrane-bound ribosomes apparently show continuities with fibrils within the cytoplasmic matrix on the one side and with filaments within the cisternae of the endoplasmic reticulum on the other. Ribosomal filaments of stromal cells also seem to have filamentous continuities with extracellular fibrils. This morphological evidence opens new perspectives concerning the role of RNA filaments in protein synthesis. Part of this work was continued during a fellowship 1974/75 at the Laboratory of Human Reproduction and Reproductive Biology, Dept. of Anatomy, Harvard Medical School, Boston supported by the Ford Foundation. The author thanks Dr. D.W. Fawcett for making this fellowship available. This study was supported by the Deutsche Forschungsgemeinschaft
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00219854
