Arrangement Of Ribosomes Research Articles

Elucidation of Spatial Positioning of Ribosomes around Chromosome in Escherichia coli Cytoplasm via a Data-Informed Polymer-Based Model.

The spatial arrangement of ribosomes and chromosome in Escherichia coli's cytoplasm challenges conventional wisdom. Contrary to the notion of ribosomes acting as inert crowders to the chromosome in the cytoplasm, here we propose a nuanced view by integrating a wide array of experimental data sets into a polymer-based computer model. A set of data-informed computer simulations determines that a delicate balance of attractive and repulsive interactions between ribosomes and the chromosome is required in order to reproduce experimentally obtained linear densities and brings forth the view that ribosomes are not mere inert crowders in the cytoplasm. The model finds that the ribosomes represent themselves as a poor solvent for the chromosome with a 50 nm mesh size, consistent with previous experimental analysis. Our multidimensional analysis of ribosome distribution, both free (30S and 50S) and bound (70S polysome), uncovers a relatively less pronounced segregation pattern than previously thought. Notably, we identify a ribosome-rich central region within the innermost core of the nucleoid. Moreover, our exploration of the chromosome mesh size and the conformation of bound ribosomes suggests that these ribosomes maintain elongated shapes, enabling them to navigate through the chromosome mesh and access the central core. This dynamic localization challenges the static segregation model and underscores the pivotal role of ribosome-chromosome interactions in cellular media.

Ribosome heterogeneity in Drosophila melanogaster gonads through paralog-switching

Ribosomes have long been thought of as homogeneous macromolecular machines, but recent evidence suggests they are heterogeneous and could be specialised to regulate translation. Here, we have characterised ribosomal protein heterogeneity across 4 tissues of Drosophila melanogaster. We find that testes and ovaries contain the most heterogeneous ribosome populations, which occurs through a combination of paralog-enrichment and paralog-switching. We have solved structures of ribosomes purified from in vivo tissues by cryo-EM, revealing differences in precise ribosomal arrangement for testis and ovary 80S ribosomes. Differences in the amino acid composition of paralog pairs and their localisation on the ribosome exterior indicate paralog-switching could alter the ribosome surface, enabling different proteins to regulate translation. One testis-specific paralog-switching pair is also found in humans, suggesting this is a conserved site of ribosome heterogeneity. Overall, this work allows us to propose that mRNA translation might be regulated in the gonads through ribosome heterogeneity, providing a potential means of ribosome specialisation.

Ultrastructure of erythrocytic stages of avianPlasmodiumspp. of the sub-genusNovyellaand its “globule”

A globule frequently refractory, appearing blue, pale blue, or white with Giemsa stain, is characteristic of the intraerythrocytic stages of the type species and of most of the other species included at present in the subgenus Novyella. This globule is absent from the other Plasmodium sub-genera. An ultrastructural study has been performed on schizogonic stages of Plasmodium merulae from the blood of the blackbird, Turdus merula. In section the globule contains a finely granular substance suggesting a condensed or coagulated substance. It differs distinctly from a classical food vacuole by denser contents, and show in some sections (19, 23) a peripheral opaque rim with a radial arrangement of ribosomes. Except for the presence of the globule, in other details P. merulae do not diverge from the ultrastructure common to the intraerythrocytic stages of avian Plasmodium.

Ribosomes Associated with the Mitochondrial Surface of the Yeast Rhodotorula minuta1)

Summary Electron microscopical observations of the yeast Rhodotorula minuta HARRISON, aerobically and unaerobically cultured in liquid agar, revealed a unique covering of the mitochondrial surface by presumptive 80S ribosomes. Their pattern of distribution and their association to the outer mitochondrial membrane are emphasized in comparison with the ribosomal arrangement of the endoplasmic reticulum of higher plant cells.

Effect of Some Nucleic Acid Base Analogues and Inhibitors of Protein Synthesis on Orderly Arrangement of Ribosomes in Callus Tissue of Corylus avellana

An embryogenic callus tissue of hazel (Corylus avellana) was used in this study. The meristematic cells of this tissue generate a characteristic rough endoplasmic reticulum (RER) with orderly arrays of bound ribosomes. Some nuclei-acid base analogues and inhibitors of protein synthesis were employed in order to study their action on the formation of these orderly arrays Puromycin did not affect the appearance of RER aggregates and ribosome pairing, although it seemed to reduce their frequency. Cycloheximide, 2-aminopurine and 5-bromouracil suppresed the formation of RER aggregates as well as the pairing of ribosomes. It is concluded that proper nucleic acid and protein synthesis ensuring ribosomal integrity are essential for the structural interaction resulting in the orderly arrays of membrane-bound ribosomes, which are probably pools of ribosomes held in reserve until their recruitment for embryogenesis.

Myofilament-polyribosome association in muscle cells of rat left atrium after short-term hypertension.

Hypertension was induced in uninephrectomized Wistar rats by administration of deoxycorticosterone acetate (DOCA) and by addition of NaCl to their drinking water. The ultrastructure of atrial and ventricular cells of left hearts was compared after short-term (2 and 6 weeks) increased blood pressure. No morphological features could distinguish cells of treated animals from cells of normotensive rats after 2 weeks of treatment. The sarcoplasm of the atrial cells of 6-week-treated hypertensive rats presented an abnormally high number of helical arrangement of ribosomes often associated with abundant unorganized thick filaments, irregular nuclear profiles showing foldings and convolutions, and enlarged mitochondria. The only fine structural changes observed in the ventricular cells of the same animals was a moderate mitochondrial enlargement. The described alterations of atrial cells probably correspond to enhanced synthesis of contractile elements associated with increased nuclear-cytoplasmic exchanges; their absence in ventricular cells suggests that short-term and moderate pressure overload induces adaptative changes in left atrial cells at a stage when ventricular cells have morphological characteristics close to normal cells.

Morphological evidence for the stimulatory effect of insulin on vaginal and endometrial cells of rats.

The effect of insulin (single subcutaneous injection 3 IU/100 g body weight) on the vaginal epithelium cells was studied in castrated adult female rats. At the electron-microscopic level, the vaginal cells showed development of the Golgi complexes and increase in the number and arrangement of ribosomes and secretory vesicles. The endometrial cells showed similar modifications, with stronger evidence of neoformation of polyribosomes. These results suggest that insulin stimulates the cellular activity of the vaginal and endometrial epithelia of castrated female rats.

Light microscopical and ultrastructural observations on the effect of vinblastine on ameloblasts of rat incisors in vivo. I. Short-term effect on secretory ameloblasts.

The highly polarized secretory ameloblasts in the incisors of rats fixed by perfusion with glutaraldehyde two or three hours after intravenous administration of vinblastine sulfate at a dosage of 5 mg per 100 g body weight were studied in the light microscope and the electron microscope. The following effects were observed: 1. All cytoplasmic microtubules in the ameloblasts had vanished. This was not accompanied by the appearance of paracrystals of microtubular protein or macrotubules. 2. The ameloblasts preserved their external features of polarized cells but lost their ability to maintain normal orderly segregation of the cell constituents; i.e. their normal internal compartmentalization and polarity had vanished. 3. The ameloblasts lost their capability of directional translocation of the secretory granules towards the cell apex. 4. Secretory granules already translocated to the cell apex regurgitated in the cell and a probably delayed discharge of secretory material had started in abnormal site at the surface. 5. The normal arrangement of ribosomes into polyribosomes on the membranes of the rough endoplasmic reticulum was no longer present; the ribosomes were apparently distributed at random. 6. New secretion was inhibited or brought to a standstill but secretory material already present in the Golgi complex appeared to be transported normally. 7. The centriole had started to develop into a cilium in many of the cells. 8. The number of autophagic vacuoles had increased.

Orderly arrangement of ribosomes in the embryogenic callus tissue of Corylus avellana L.

Cultured callus tissue of hazel (Corylus avellana L.), which has the potency of somatic embryogenesis, was used for the study of cell ultrastructure in the course of callus growth and embryoid formation. The meristematic cells of this tissue exhibit a specific organization of rough endoplasmic reticulum (RER), stacked into extensive parallel sheets. The membranes of the aggregated RER are associated with orderly arrays of bound ribosomes. The high regularity of the alignment of the attached ribosomes seems to be influenced by the distance between the two neighbouring membranes in the RER aggregate. The RER aggregates with orderly attached ribosomes are more frequently found in callus cells and in early embryogenesis than in the advanced stages of embryo development.

The arrangement of ribosomes in ribosome tetramers from hypothermic chick embryos.

1. Ribosomes and the tetramer arrangement peculiar to the tissues of chick embryos exposed to low temperatures were separated by sucrose-density-gradient centrifugation, and the effects of variation of the concentrations of Mg(2+), Ca(2+) and K(+) studied. 2. Lowering of the Mg(2+) concentration from standard buffer conditions caused a reversible dissociation of tetramers into monomers and of these into subunits. 3. Ca(2+) replaced Mg(2+) in causing the re-formation of tetramers and monomers from subunits after dissociation in low Mg(2+) concentrations. 4. Ca(2+) also caused an almost complete conversion of monomers into dimers in the presence of Mg(2+). 5. The effect of Ca(2+) on the formation of dimers was abolished by pretreatment of the ribosomes with ribonuclease, but the re-formation of tetramers was unaffected. 6. Increase of the K(+) concentration from that of the standard buffer caused dissociation of monomers and dimers into subunits. 7. Raised K(+) concentration also caused a stepwise alteration of the tetramer from a particle with a sedimentation coefficient of 197S, which constitutes the bulk of the tetramer at low K(+) concentrations, first to a 184S peak and finally to material with a sedimentation coefficient of about 155S. 8. The implications of these results on hypotheses of the arrangement of the individual monomers in the tetramer are discussed and a new model for the structure is proposed.

Mucilage-Producing Cells in the Seed Coat of Plantago ovata: Developmental Fine Structure

As the ovule of Plantago ovata matures into a seed its epidermal cells are transformed from undifferentiated parenchyma to thin-walled containers of almost pure mucilage. During this process the volume of the cells increases 60–80 fold, and the protoplast degenerates to a remnant. Rapid cell expansion begins with pollination and is accompanied by an increase in the size of the nucleus and nucleolus, a change in the random arrangement of ribosomes, a decrease in the thickness of cell walls, and synthesis of starch. Deposition of mucilage inside vacuoles and between the plasma membrane and cell wall accompanies a marked increase in the number and size of Golgi vesicles. Histochemical evidence using the thiocarbohydrazide-osmium vapor method shows polysaccharide to be present within Golgi vesicles while they are still attached to the Golgi apparatus. Mucilage deposition is associated with further cell expansion, separation of the protoplast from the cell wall, fusion of vacuoles and extra protoplasmic space, and the disappearance of starch.

MUCILAGE‐PRODUCING CELLS IN THE SEED COAT OF PLANTAGO OVATA: DEVELOPMENTAL FINE STRUCTURE

As the ovule of Plantago ovata matures into a seed its epidermal cells are transformed from undifferentiated parenchyma to thin‐walled containers of almost pure mucilage. During this process the volume of the cells increases 60–80 fold, and the protoplast degenerates to a remnant. Rapid cell expansion begins with pollination and is accompanied by an increase in the size of the nucleus and nucleolus, a change in the random arrangement of ribosomes, a decrease in the thickness of cell walls, and synthesis of starch. Deposition of mucilage inside vacuoles and between the plasma membrane and cell wall accompanies a marked increase in the number and size of Golgi vesicles. Histochemical evidence using the thiocarbohydrazide‐osmium vapor method shows polysaccharide to be present within Golgi vesicles while they are still attached to the Golgi apparatus. Mucilage deposition is associated with further cell expansion, separation of the protoplast from the cell wall, fusion of vacuoles and extra protoplasmic space, and the disappearance of starch.

Studies of fibrinogen synthesis in rats fed thrombogenic diets

In rats fed complex high fat-cholesterol diets serum lipids and various coagulation factors, including plasma fibrinogen, prothrombin, factors V and VIII, and fibrin-stabilizing factor, were elevated as compared to stock-fed rats. The exact mechanism accounting for the increase in these factors is not clear. In the current experiments we have selected fibrinogen from among the coagulation factors for study of possible mechanism leading to its elevation. Plasma fibrinogen levels in the high fat-cholesterol group increased two- to three-fold, while C 14-glycine incorporation into fibrinogen in vivo was reduced to less than 10% of control values. These changes began to take place as early as two days after dietary feeding is started. Amino acid incorporation under these circumstances is not necessarily a measure of protein synthesis but does provide us with at least a comparative rate of synthesis. Our data suggest that very likely the elevated plasma fibrinogen level is due to a decreased rate of degradation rather than to increased synthesis. In a cell-free system including microsomes and “supernatant” from liver, oxidative substrate and cofactors required for oxidative phosphorylation and ATP generation, C 14-leucine incorporation into microsomal protein and response of C 14-phenylalanine incorporation to poly U were markedly reduced in the high fat-cholesterol fed rats as compared to stock-fed rats. The difference in radioactive amino acid incorporation into polysomal protein between the two groups however was slight, and the response of C 14-phenylalanine incorporation to poly U was approximately the same in the two groups. Major differences in the ultrastructure of the liver between the two groups were the appearance of rough-surfaced endoplasmic reticulum, characteristic arrangement of ribosomes and presence of lipid in the cytoplasm. In the high fat-cholesterol group endoplasmic reticulum usually appeared disorganized and cisternae irregularly distended. Characteristic rosette or spiral patterns were much less common than in a stock-fed rat and numerous lipid droplets were usually seen. Chemical determinations of RNA content suggest that there is actual decrease in the number of ribosomes in the liver of high fat-cholesterol fed rats. This decrease and the disturbances in arrangement of ribosomes observed by electron microscopy may contribute to the biochemical defects that were demonstrated. However, demonstration of association by itself is not sufficient to warrant more specific conclusions.

Helical arrangement of ribosomes in the cytoplasm of differentiating cells of the small intestine of rat foetuses

Helical arrangement of ribosomes in the cytoplasm of differentiating cells of the small intestine of rat foetuses

Helical arrangement of ribosomes in differentiating muscle cells

Helical arrangement of ribosomes in differentiating muscle cells