Characterization of mitochondrial and cytoplasmic ribosomes from Paramecium aurelia

Immunoelectron microscopical studies on synthesis and localization of uncoupling protein in brown adipocytes: evidence for cotranslational transport of uncoupling protein into mitochondria

Through the use of the immunoelectron microscopical technique, uncoupling protein (UCP) was analyzed in the brown adipocytes of room temperature- and cold-acclimated rats, in rat brown adipocytes developed in vitro, and in the brown adipocytes of mice, hamsters, and hedgehogs. Using rat anti-UCP-antibody, it is shown that UCP is located in the cristae of brown adipocytes mitochondria (UC-mitochondria) of all analyzed species, whereas mitochondria of nonadipose cells, i.e., C-mitochondria of endothelium, fibrocytes, smooth muscle cells, Schwann cells, axons of neural cells, and white blood cells, do not contain UCP. Cold stress in rats exposed to temperatures of +4 and -20 degrees C caused the amount of UCP per 1 micron 2 of mitochondria to more than double compared with room temperature-acclimated rats. This increase was especially dramatic on the outer mitochondrial membrane: fourfold more UCP molecules compared to the control rats. The ground cytoplasm of adipocytes showed very intensive labeling with RNase-gold complex, indicating that cytoplasm was an active site for protein synthesis, while the absence of UCP-labeling in ground cytoplasm was interpreted to mean that ground cytoplasm did not serve as a site for UCP synthesis. On the other hand, the protrusions of the outer mitochondrial membrane covered with ribosomes, clusters of UCP molecules, and clusters of RNase-gold particles supported the idea that UCP was one of the mitochondrial proteins synthesized on the ribosomes which were in contact with the outer mitochondrial membrane. After being synthesized there, UCP, which could be either extruded into intermembranous space or directed by lateral movement to intermembranous contact sites, was incorporated into inner mitochondrial membrane. Thus, UCP is imported using the so-called "cotranslational transport system."

Characterization of mesosomes of Micrococcus luteus: isolation and properties of mesosomal ribosomes, and localization of penicillin-binding proteins in mesosomal membranes

Mesosomes were isolated and purified from Micrococcus luteus under hypertonic conditions throughout preparation processes. The purified mesosomal preparation was composed of closed tubules and vesicles. Electron-dense ribosome-like particles were observed within the isolated mesosomal vesicles by electron microscopy. The ribosome-like particles were isolated from the purified mesosomes by a procedure involving solubilization of the membranes with detergents followed by centrifugation on a linear density gradient of sucrose. The isolated particles have a sedimentation coefficient of 70S in the presence of 10 mM Mg2+, when Mg2+ concentration was lowered to 0.1 mM, the particles were dissociated into two sub-particles of 30S and 50S. The 70S particles had the same appearance as cytoplasmic 70S ribosome particles upon observations of negatively stained preparations. These findings indicate that mesosomal tubules contain ribosomes. The isolated mesosomal ribosomes had the ability for protein synthesis when polyuridylic acid-directed polyphenylalanine synthesis was assayed. The sensitivity of mesosomal ribosomes to inhibitors, chloramphenicol and streptomycin, for protein synthesis was significantly lower than that of both cytoplasmic and cytoplasmic membrane-bound ribosomes. In addition, three penicillin-binding proteins were detected in the mesosomal membranes. One of these was localized predominantly in the mesosomal membranes and the other two were distributed almost equally in both mesosomal and cytoplasmic membranes.

The mitoribosomes of a chloramphenicol-resistant cytoplasmic mutant of Tetrahymnea pyriformis differ from those of the wild strain

The spontaneous CAP-resistant mutant, STR1, has been isolated from the sensitive St-strain of Tetrahymena pyriformis (Curgy et al., Biologie Cellulaire 37, 51-60, 1980; Perasso et al., Biologie Cellulaire 37, 45-50, 1980). The goal of the present work is to disclose if the resistance character is due to a modification in the mitoribosomes and if the CAP-treatment induces changes in their abundance and in their physico-chemical properties.The results show that the resistance character of the mutant is due to a reduced affinity of its mitoribosomes for CAP. This difference can be explained by modifications of at least one protein which is probably coded for by the mitochondrial genome.The mitoribosomes from CAP-treated sensitive cells tend to dissociate into their subunits and the electrophoretic pattern of their proteins suggests that at least two mitoribosomal proteins are necessary to bound the two subunits together. These proteins are probably translated in mitochondria.Finally, the CAP-treatment induces a decrease of the abundance of mitoribosomes in the sensitive cells whereas it induced an increase in the resistant cells. The latter change can be regarded as a regulatory mechanism owing to which a loss of efficiency of the mitoribosomes is compensated by their enlarged abundance.

Anatomy of mitochondrial DNA from Paramecium aurelia

The linear genome of mitochondrial DNA from four species of Paramecium aurelia was investigated with respect to restriction endonuclease fragments, location and number of ribosomal RNA genes, and interspecies EcoRI and HindIII fragment homologies. One copy of each of the rRNA genes was found in all four species and the 14s and 20s rRNA genes were separated by at least 3,000 bp. R-Loop analysis of the 20s rRNA gene did not reveal the presence of an intervening sequence. Interspecies homology studies showed species 1, 5, and 7 to have a high degree of homology but species 4 was less than 50% homologous to species 1 mt DNA. For all four species, rRNA genes showed good homology indicating that these DNA sequences are highly conserved, even between species having many non-homologous regions. A major region of DNA which displayed little homology between species 1 and 4 was that fragment containing sequences essential for initiation of DNA replication.

Physiological consequences of mitochondrial antibiotic-resistant mutations in Paramecium: growth-rates, cytochromic defects and cyanide-insensitive respiration of mutant and erythromycin-treated wild-type strains

A set of mitochondrial antibiotic-resistant mutants of Paramecium have been analyzed with respect to their growth-rates, cytochromic content and respiratory properties. The mutants could be arranged in a continuous series ranging from strains equivalent to wild-type to severely affected ones; affected strains display longer generation times, reduced amount of cytochrome oxidase and very high levels of cyanideinsensitive respiration. Perfect phenocopies of the mutants were obtained by treating wild-type cells with low concentrations of erythromycin suggesting that the mutations exert their pleiotropic effect by perturbating mitochondria protein synthesis in agreement with the idea that these mutations affect the mitochondrial ribosomes. In the mitochondria of some of the mutants, electrons can be channelled with equal efficiency into the "classical" cyanide-sensitive pathway and the alternate cyanide insensitive (and SHAM-sensitive) one, providing direct demonstration of the branching of these two respiratory pathways. In the absence of any added inhibitor, however, electrons tend to be channelled in the cyanide-sensitive pathway. All the physiological data fit perfectly the genetic data concerning the "stability" of the various mutations in "mixed mitochondrial populations", i.e., markers that were known to be strongly counter-selected with respect to wild-type in such populations correspond to severely affected strains, while markers that were known to be "stable" correspond to "healthy" strains. A more quantitative analysis of the data shows that that there is little or no "complementation" between wild-type and mutated mitochondria in mixed cells indicating a high extent of functional autonomy of mitochondria in Paramecium.