Industrial yeast strain improvement: construction of strains having the killer character and capable of utilizing starch

Summary A hybrid of Saccharomyces cerevisiae with the ability to utilize starch and to produce the killer toxin was constructed by the protoplast fusion technique. The hybrid was obtained in two steps. In the first, a wild killer strain was fused with a laboratory strain (S. cerevisiae STA2). A fusion product which carried the killer factor and the ability to grow on starch was selected. In the second step, this hybrid was fused with a baker's yeast.     

Frequency of the ΔF508 deletion and G551D,R553X and G542X mutations in Yugoslav CF patients

Summary A study was undertaken to find the frequency of the F508 deletion and those of the G551D, R553X and G524X mutations among the mainly Slavic population of Serbia, Bosnia, Herzegovina, and Montenegro and compare the frequencies determined with those in other European populations. The F508 mutation was found to account for about 70% of CF genes in central Jugoslavia, where its frequency is significantly higher than elsewhere in Southern European populations.     

Contrasting breeding systems in twoEriotheca (Bombacaceae) species of the Brazilian cerrados

The pollination biology and breeding systems ofEriotheca pubescens andE. gracilipes have been studied. These two species occur as trees in cerrado vegetation, the neotropical savannas of Central Brazil, with partially sympatric distributions. They have similar phenology and floral structure, although the flowers ofE. pubescens are larger. Both species have nectar flowers pollinated by largeAnthophoridae bees but the main pollinators of each species differ in size. The species have markedly different breeding systems: late-acting self-incompatibility inE. gracilipes and apomixis stimulated by pollination inE. pubescens.     

The spo0A gene is implicated in the maintenance of non-complementing diploids in Bacillus subtilis

Bacillus subtilis can exist in a diploid state in which two genetically distinct chromosomes co-exist in the same cell and yet only one of them is expressed, thereby determining the phenotype. Such cells are called non-complementing diploids (Ncds). In this study, two types of experiments are reported which indicate that a previously known pleiotropic gene, spo0A, plays a role in the maintaining the diploid state, as follows. (i) When protoplasts of two Spo0A mutant strains were fused, the resulting products continued to segregate cells of both parental phenotypes for many more divisions than had been reported previously. (ii) When a stable Ncd (an Ncd in which the unexpressed markers are not spontaneously activated at a detectable level) harbouring a chloramphenicol acetyltransferase gene on the silent chromosome was transformed with spo0A null alleles the transformants often expressed chloramphenicol acetyltransferase activity. Together these results indicate that the spo0A gene is involved in maintenance of the diploid state in both unstable and stable Ncds.     

Mechanism of action of levonorgestrel: in vitro metabolism and specific interactions with steroid receptors in target organs.

Levonorgestrel (LNG) is a synthetic steroid that displays potent progestional and androgenic effects but it lacks estrogen-like activity. To examine the mode of action of this progestin, we studied its metabolism in vitro in target organs and the specific interactions of LNG and its metabolites with putative steroid receptors. The results demonstrated that [³H]LNG was efficiently converted to A-ring reduced derivatives when incubated with rat hypothalamus and pituitary. Under optimal incubation conditions, [³H]5-dihydro LNG (5-LNG) and [³H]3-5-tetrahydro LNG (3,5-LNG) were identified as the major metabolic conversion products, while [³H]3ß, 5-LNG formation occured to a lesser extent. A-ring reduction of LNG was NADPH-dependent. Assessment of the relative binding affinities of LNG and its derivatives to progesterone (PR), androgen (AR) and estrogen (ER) receptors by displacement analysis revealed that unchanged LNG binds with high affinity to PR and AR but not to ER. 5-LNG exhibited a diminished though significant interactions with PR and an enhanced binding affinity for AR as compared with LNG, indicating that 5-reduction of LNG increases its affinity for AR. The most striking finding was that further reduction of the 5-LNG molecule at C-3 abolished its binding activity to PR, AR, and even to ER. The overall data provides a plausible explanation for the lack of estrogen agonistic action of LNG and for its potent progestational and androgenic effects.     

Glutamic acid decarboxylase of embryonic avian retina cells in culture: Regulation byγ-aminobutyric acid (GABA)

1. Retina-cell aggregate cultures expressed glutamate decarboxylase activity (L-glutamate 1-carboxylase; EC 4.1.1.15) as a function of culture differentiation. 2. Glutamic acid decarboxylase (GAD) activity was low in the initial phases of culture and increased eight-fold until culture day 7, remaining high up to day 13 (last stage studied). 3. The addition of GABA to the culture medium 24 h after cell seeding almost totally prevented the expression of GAD activity. 4. In association with decreased enzyme activity, aggregates exposed to GABA did not display immunoreactivity for GAD, suggesting that GAD molecules were either lost from GABAergic neurons or significantly altered with GABA treatment. 5. Control, untreated aggregates showed intense GAD immunoreactivity in neurons. Positive cell bodies were characterized by a thin rim of labeled cytoplasm with thickest labeling at the emergence of the main neurite. 6. Heavily labeled patches were also observed throughout the aggregates, possibly reflecting regions enriched in neurites. 7. The GABA-mediated reduction of GAD immunoreactivity was a reversible phenomenon and could be prevented by picrotoxin.     

Purification and properties ofl-serine dehydratase fromLactobacillus fermentum ATCC 14931

l-Serine dehydratase fromLactobacillus fermentum was purified 100-fold. It was stabilized by the presence of 1 mM l-cysteine in 50 mM phosphate buffer. M_r=150,000 was determined by gel filtration. The enzyme consists of four apparently identical subunits (M_r=40,000) that were observed after treatment with sodium dodecyl sulfate. The apparent K_m forl-serine was 65 mM. Fe⁺⁺ was required for the enzymatic activity, and the apparent K_m value for this reaction was 0.55 mM. Maximum enzymatic activity was observed at 45°C and pH 8.0 in 50 mM phosphate buffer. At pH values different from the optimum, a positive cooperativity between substrate molecules was observed. The activation energy of the reaction was 11,400 and 22,800 cal × mol^–1 for temperature values more than and less than 35°C respectively. The purified enzyme showed a maximum absorption between 400 and 420 nm, indicating the presence of pyridoxal-5-phosphate (PLP) as a prosthetic group. The PLP concentration was 0.027 µmoles per milligram of protein. The data suggest that there is 1 mol of PLP for each protein subunit.     

Stomatal response to air humidity and its relation to stomatal density in a wide range of warm climate species

The gas exchange of 19 widely different warm climate species was observed at different leaf to air vapour pressure deficits (VPD). In all species stomata tended to close as VPD increased resulting in a decrease in net photosynthesis. The absolute reduction in leaf conductance per unit increase in VPD was greatest in those species which had a large leaf conductance at low VPDs. This would be expected even if stomata of all species were equally sensitive. However the percentage reduction in net photosynthesis (used as a measure of the relative sensitivity of stomata of the different species) was also closely related to the maximal conductance at low VPD. Similarily the relative sensitivity of stomata to changes in VPD was closely related to the weighted stomatal density or crowding index.The hypothesis is presented that stomatal closure at different VPDs is related to peristomatal evaporation coupled with a high resistance between the epidermis and the mesophyll and low resistance between the stomatal apparatus and the epidermal cells. This hypothesis is consistent with the greater relative sensitivity of stomata on leaves with a high crowding index.The results and the hypothesis are discussed in the light of selection, for optimal productivity under differing conditions of relative humidity and soil water availablility, by observation of stomatal density and distribution on the two sides of the leaf.Visiting scientist, plant physiologist and research assitant of the Cassava Program