Structure of rough, smooth, stripped and reconstituted rough membranes derived from rat liver as visualized by the freeze fracture technique

Substructure of cisternal organelles of neuronal perikarya in immature rat brains revealed by quick-freeze and deep-etch techniques

Membrane-bounded organelles possessing cisternae, i.e., rough endoplasmic reticulum and Golgi apparatus, in immature rat central neurons were examined by quick-freeze and deep-etch techniques to see how their intracisternal structures are organized and how ribosomes are associated with the membrane of the endoplasmic reticulum. Cisternae of endoplasmic reticulum, 60-100 nm wide, were bridged with randomly-distributed strands (trabecular strands, 12.5 nm in mean diameter). Luminal surfaces of cisternae of the endoplasmic reticulum were decorated with various-sized globular particles, some as small as intramembrane particles, and others as large as granules formed by soluble proteins seen in the cytoplasm. A closer examination revealed much thinner strands (3.3 nm in mean diameter). Such thin strands were short, usually winding toward the luminal surface, and sometimes touching the luminal surface with one end. Ribosomes appeared to be embedded into the entire thickness of cross-fractured membranes of endoplasmic reticulum, that is, their internal portions appeared to be situated at almost the same level as the cisternal luminal surface. From the internal portion of ribosomes, single thin strands occasionally protruded into the lumen, suggesting that these thin strands were newly synthesized polypeptides. A horizontal separation within ribosomes appeared to occur at the same level as the hydrophobic middle of the membrane of the endoplasmic reticulum. Interiors of the Golgi apparatus cisternae, which were much narrower than cisternae of endoplasmic reticulum, were similarly bridged with trabecular strands, but the Golgi trabecular strands were thinner and more frequent. Their cisternal lumina were also dotted with globular particles. No identifiable profiles corresponding to the thin strands in the endoplasmic reticulum were observed. Golgi cisternae showed a heterogeneous distribution of membrane granularity; the membrane in narrow cisternal space was granule-rich, while that in expanded space was granule-poor, suggesting a functional compartmentalization of the Golgi cisternae.

Mechanism of RNA redistribution of the 17,000g postmitochondrial supernatant after incubation at 37 degrees C and its impact on other related biochemical investigations

Evidence for stripping of ribosomes from RER in the 17,000g PMS of the liver of the cancer patient was obtained in the 1.35 M region which is the region between the SER and RER. RNA/protein ratios for the SER, 1.35 M region, and RER of 0.001, 0.083, and 0.235, respectively, for this liver are consistent with the degranulation of RER compared with RNA/protein ratios for SER and RER from normal livers of 0.025 +/- 0.003, and 0.35 + 0.030, respectively. A RNA/protein ratio of 0.235 was obtained for the RER region of the cancer patient. The EM revealed that the region of the RER in the cancer liver was ribosomal and not at all RER. This ribosomal material is reminiscent of the ribosomes banding in the 1.35- to 2 M domain of the RER isolated from the reconstitution experiments (SER + polyribosomes + supernatant). It was suggested that the ribosomal material isolated from the cancer liver could therefore be indicative of polyribosomal lesion or degradation. The 0.25-1.35 M interface (SER), 1.35 M region, and 1.35-2 M interface (RER) characteristics are therefore exploitable for diagnostic potential and further understanding of the molecular basis of cancer.

Ribosome binding sites visualized on freeze-fractured membranes of the rough endoplasmic reticulum

Freeze-fracture micrographs of cells of the green alga Micrasterias denticulata stabilized by ultrarapid freezing reveal imprints of polysomes on the rough endoplasmic reticulum membranes. The imprints appear as broad, spiral ridges on the P faces and as corresponding wide grooves on the E faces of the membranes. Distinct 110-A particles with a spacing of 270 +/- 45 A are associated with the P-face ridges. Where imprints of individual ribosomes can be discerned, it is seen that there is a 1:1 relationship between the ribosomes and the 110-A particles, and that the 110-A particles are located in a peripheral position with respect to the polysome spirals. We propose that the 110-A particles could be structural equivalents of ribosome-binding sites, consisting of a molecule each of ribophorins I and II and a nascent polypeptide chain. These observations suggest that the spiral form of polysomes could result from the forces generated by the extrusion of the growing polypeptide chains to one side of the polysome.

Effect of ethionine on the rough endoplasmic reticulum from male and female rat liver

Ethionine causes a decrease in the amount of rough endoplasmic reticulum in rat liver, the effect being greater in female than in male rats. Rough endoplasmic reticulum isolated from rat liver 24 hr after ethionine injection and stripped of its ribosomes partially lost its in vitro ribosome binding capacity. However, no differences were detected between the binding affinities of ribosomes, isolated from either untreated animals or intoxicated rats, to stripped rough membranes derived from normal rats. Structural changes occur in the rough endoplasmic reticulum of the ethionine treated rats, while the ribosomes are still bound to the membrane.

Mobility of ribosomes bound to microsomal membranes. A freeze-etch and thin-section electron microscope study of the structure and fluidity of the rough endoplasmic reticulum

The lateral mobility of ribosomes bound to rough endoplasmic reticulum (RER) membranes was demonstrated under experimental conditions. High-salt-washed rough microsomes were treated with pancreatic ribonuclease (RNase) to cleave the mRNA of bound polyribosomes and allow the movement of individual bound ribosomesmfreeze-etch and thin-section electron microscopy demonstrated that, when rough microsomes were treated with RNase at 4 degrees C and then maintained at this temperature until fixation, the bound ribosomes retained their homogeneous distribution on the microsomal surface. However, when RNase-treated rough microsomes were brought to 24 degrees C, a temperature above the thermotropic phase transition of the microsomal phospholipids, bound ribosomes were no longer distributed homogeneously but, instead, formed large, tightly packed aggregates on the microsomal surface. Bound polyribosomes could also be aggregated by treating rough microsomes with antibodies raised against large ribosomal subunit proteins. In these experiments, extensive cross-linking of ribosomes from adjacent microsomes also occurred, and large ribosome-free membrane areas were produced. Sedimentation analysis in sucrose density gradients demonstrated that the RNase treatment did not release bound ribosomes from the membranes; however, the aggregated ribosomes remain capable of peptide bond synthesis and were released by puromycin. It is proposed that the formation of ribosomal aggregates on the microsomal surface results from the lateral displacement of ribosomes along with their attached binding sites, nascent polypeptide chains, and other associated membrane proteins; The inhibition of ribosome mobility after maintaining rough microsomes at 4 degrees C after RNase, or antibody, treatment suggests that the ribosome binding sites are integral membrane proteins and that their mobility is controlled by the fluidity of the RER membrane. Examination of the hydrophobic interior of microsomal membranes by the freeze-fracture technique revealed the presence of homogeneously distributed 105-A intramembrane particles in control rough microsomes. However, aggregation of ribosomes by RNase, or their removal by treatment with puromycin, led to a redistribution of the particles into large aggregates on the cytoplasmic fracture face, leaving large particle-free regions.