Ribosomal recessive suppressors cause a respiratory deficiency in yeast Saccharomyces cerevisiae

Summary Recessive suppressor mutations in yeast Saccharomyces cerevisiae alter a component of the cytoplasmic ribosomes, relaxing the control of translational fidelity. As a consequence ribosomes can misread nonsense codons as amino acids (Surguchov et al. 1980a).The suppressor mutants are often respiratory deficient, being unable to grow on non-fermentable substrates. The study of the cytochrome spectra has revealed that the cytochrome b and aa₃ contents were lower in the mutants than in the parent strains. Furthermore, the suppresor mutations often cause hypersensitivity to paromomycin and neomycin on media with a non-fermentable source of carbon. Some of the suppressor mutants exhibited both erythromycin and chloramphenicol-dependent growth on media containing ethanol or glycerol as a sole carbon source.These results suggest that the mutations altering cytoplasmic ribosomes may simultaneously impair the mitochondrial translation. A coupling of cytoplasmic and mitochondrial protein synthesis in yeast cells is proposed. The existence of a common protein component participating both in mitochondrial and cytoplasmic protein synthesis apparatus is discussed.     

Electric field-mediated cell fusion

The use of electrical fields to guide, hold and fuse cells is described. The electrical fusion process consists of two steps: the cells are collected to form pearl-chains between Pt electrodes by the action of dielectrophoresis, then a brief DC pulse is applied, such that the breakdown voltage of the membranes is briefly exceeded and cell-to-cell juncture of the membranes occurs around the pore formed by the pulse. Giant fused cells (diameter up to 100 m) can be formed by the electrically mediated fusion of mouse 3T3 fibroblast cells, provided that pronase is added just before field application.     

Mechanical stabilization of guard cell protoplasts of Vicia faba

Guard cell protoplasts of Vicia faba were immobilized in cross-linked Ca-alginate. No visible morphological changes were detected under the light microscope over a period of 14 days. The entrapped cells reacted normally to changes of the external osmolarity by shrinking and swelling. Addition of the calcium complexing agent, citrate, led to dissolution of the matrix. After reequilibration with Ca ions the released cells regained their ability to swell and shrink in response to external stress. The released protoplasts could be stained with the vital dye, neutral which was accumulated in the vacuoles. It should also be noted that the protoplasts can be transported when immobilized.     

Molecular cloning and selection of genes regulated in Aspergillus development

Over 350 clones homologous to poly(A)+ RNAs that are significantly more prevalent in conidiating cultures of Aspergillus nidulans than in somatic cells have been selected from a recombinant DNA library formed between nuclear DNA and lambda Charon 4A. The procedure used for this selection involved in situ hybridization to a cDNA probe which had been selectively depleted of sequences represented in somatic cells by complement hybridization. Five of these clones have been characterized further. All but one encoded poly(A)+ RNAs that were at least ten times more prevalent in conidiating cultures than in somatic cells. One clone hybridized to a single, developmentally regulated RNA. The three others were complementary to several RNAs having different molecular weights, each of which was more prevalent in condiating cultures than in vegetative cells. These results and quantitative aspects of the selection procedure suggest that developmentally controlled poly(A)+ RNA coding regions may not be distributed randomly in the Aspergillus genome.     

Pulse-length dependence of the electrical breakdown in lipid bilayer membranes

Charge-pulse experiments were performed on artificial lipid bilayer membranes with charging times in the range between 10 ns and 10 μs. If the membranes are charged to voltages in the order of 100 mV, the membrane voltage at the end of the charge pulse is a linear function of the injected charge. However, if the membranes are charged to voltages in the range of 1 V, this relationship no longer holds and a reversible high conductance state occurs. This state is defined as an electrical breakdown and it does not allow the membranes to charge to higher voltages than the breakdown voltage, $\text{V}{}_{\mathrm{<mtext>c</mtext>}}$. Between charging times of 300 ns and 5 μs at 25°C and between 100 ns and 2 μs at 40°C, $\text{V}{}_{\mathrm{<mtext>c</mtext>}}$ showed a strong dependence on the charging time of the membrane and decreased from 1.2 to 0.5 V (25°C) and from 1 to 0.4 V (40°C). For other charging times below and above these ranges, the breakdown voltage seemed to be constant. The results indicate that the breakdown phenomenon occurs in less than 10 ns.The pulse-length dependence of the breakdown voltage is consistent with the interpretation of the electrical breakdown mechanism in terms of the electromechanical model. However, it seems possible that below a charging time of the membrane of 300 ns (25°C) and 100 ns (40°C) other processes (such as the Born energy) become possible.     

Intracerebroventricular ACTH activates the pituitary-adrenal system:dissociation from a behavioral response.

In the rat, intracerebroventricular injection of synthetic ACTH (ACTH_1–24, ACTH_1–16) elevated plasma corticosterone levels and induced the display of excessive grooming behavior. The grooming response could be elicited in hypophysectomized rats without concommittant elevation of plasma corticosterone. In intact rats subcutaneous injection of ACTH_1–24 and not of ACTH_1–16-NH₂ stimulated the release of adrenal corticosteroids, whereas no excessive grooming was observed. In contrast to the reduced effectiveness of a second icv injection of ACTH in inducing the behavioral response, no single-dose tolerance was observed for the effect of icv ACTH on the pituitary-adrenal system. Therefore it was concluded that two different central mechanisms underly the observed responses to the icv applied ACTH.     

Distribution of a Fatty Acid cyclase enzyme system in plants

Extracts from tissues of 24 plant species were tested for the enzyme that catalyzes the conversion of 13-l-hydroperoxy-cis-9,15-trans-11-octadecatrienoic acid to the cyclic fatty acid 12-oxo-cis-10,15-phytodienoic acid. The enzyme was detected in 15 of the 24 tissues examined, and was demonstrated in seedlings, leaves, and fruits.     

Dominant versus recessive behavior of a cold- and a heat-sensitive mammalian cell cycle variant in heterokaryons

A heat-sensitive (hs, arrested at 39.5 degrees C, termed 21-Ta) and a cold-sensitive (cs, arrested at 33 degrees C, termed 21-Fb) clonal cell cycle variant were isolated from the same clone of the P-815 murine mastocytoma line. At the respective nonpermissive temperatures, both the hs and the cs variant were reversibly arrested in G1 phase, and numbers of cells forming colonies upon reincubation at the permissive temperature remained nearly constant for at least 6 days. Cells arrested in G1 by incubation at the respective nonpermissive temperatures were fused to cells of another P-815 clone (31-S) that had been arrested by serum deprivation. Upon reincubation in medium containing 10% serum for 48 h at 39.5 degrees C, 21-Ta x 31-S heterokaryons, similar to 31-S x 31-S homokaryons, entered the S phase, whereas at 33 degrees C, 21-Fb x 31-S heterokaryons, similar to 21-Fb x 21-Fb homokaryons, remained arrested in G1, indicating a recessive expression of the hs and a dominant expression of the cs phenotype.     

Genetics of carbon catabolite repression in Saccharomyces cerevisiae: genes involved in the derepression process

Summary A recessive mutant cat1-1, wild type CAT1, was isolated in Saccharomyces cerevisiae. It did not grow on glycrrol nor ferment maltose even with fully constitutive, glucose resistant maltase synthesis. It prevented derepression of isocitrate lyase, fructose-1,6-diphosphatase and maltase in a constitutive but glucose sensitive maltase mutant. Derepression of malate dehydrogenase was retarded and slowed down. Sucrose fermentation and invertase synthesis was not affected. Respiration was normal. From this mutant, two reverse mutants were isolated. One was recessive, acted as a suppressor of cat1-1 and was called cat2-1, wild type CAT2; the other was dominant and allelic to CAT1 and designated CAT1-2 ^d. CAT1-2 ^d and cat2-1 caused an earlier derepression of enzymes studied but did not affect the repressed nor the fully derepressed enzyme levels. CAT1-2 ^d and cat2-1 did not show any additive effects. It is proposed that carbon catabolite repression acts in two ways. The direct way represses synthesis of sensitive enzymes, during growth on repressing carbon sources whereas the other way regulates the derepression process. After alleviation of carbon catabolite repression, gene CAT1 becomes active and prevents the activity of CAT2 which functions as a repressor of sensitive enzyme synthesis. The CAT2 gene product has to be eliminated before derepression can actually occur. The time required for this causes a delay in derepression after the depletion of a repressible carbon source. cat1-1 cannot block CAT2 activity and therefore, derepression is blocked. cat2-1 is inactive and derepression can start after carbon catabolite repression has ceased. CAT1-2 ^d is permanently active as a repressor of CAT2 and eliminates the delay in derepression.