Physical properties of cell water in partially dried Saccharomyces cerevisiae

The equilibrium vapor pressure, the heat of vaporization, the dielectric increment, and the NMR spectra of partially dried cells were studied in Saccharomyces cerevisiae with water contents varying in the range from 25 to 0.8%. The comparative study of those physical properties suggests that physical states of the microbe can be classified into four regions in accordance with the states of the cell water: the solution region, the gel region, the mobile adsorption region, and the localized water region. Much difference in the physiological properties is found between the cells in the solution region and those in the gel region, whereas the pattern changes in physical properties take place when the cells in the gel region are dried to a further extent into the mobile or the localized region. The various modes in the molecular motion of the cell water reflected in those physical properties of the cell seem to give some insight into the biological functions of the molecule in the native as well as the dried states of the cell.     

Iron-reductases in the yeast Saccharomyces cerevisiae

Several NAD(P)H-dependent ferri-reductase activities were detected in sub-cellular extracts of the yeast Saccharomyces cerevisiae. Some were induced in cells grown under iron-deficient conditions. At least two cytosolic iron-reducing enzymes having different substrate specificities could contribute to iron assimilation in vivo. One enzyme was purified to homogeneity: it is a flavoprotein (FAD) of 40 kDa that uses NADPH as electron donor and Fe(III)-EDTA as artificial electron acceptor. Isolated mitochondria reduced a variety of ferric chelates, probably via an 'external' NADH dehydrogenase, but not the siderophore ferrioxamine B. A plasma membrane-bound ferri-reductase system functioning with NADPH as electron donor and FMN as prosthetic group was purified 100-fold from isolated plasma membranes. This system may be involved in the reductive uptake of iron in vivo.     

Aquaporins in Saccharomyces cerevisiae wine yeast

AQY1 and AQY2 were sequenced from five commercial and five native wine yeasts. Of these, two AQY1 alleles from UCD 522 and UCD 932 were identified that encoded three or four amino-acid changes, respectively, compared with the Sigma1278b sequence. Oocytes expressing these AQY1 alleles individually exhibited increased water permeability vs. water-injected oocytes, whereas oocytes expressing the AQY2 allele from UCD 932 did not show an increase, as expected, owing to an 11 bp deletion. Wine strains lacking Aqy1p did not show a decrease in spore fitness or enological aptitude under stressful conditions, limited nitrogen, or increased temperature. The exact role of aquaporins in wine yeasts remains unclear.     

Exopolyphosphatases of the yeast Saccharomyces cerevisiae

Separate compartments of the yeast cell possess their own exopolyphosphatases differing from each other in their properties and dependence on culture conditions. The low-molecular-mass exopolyphosphatases of the cytosol, cell envelope, and mitochondrial matrix are encoded by the PPX1 gene, while the high-molecular-mass exopolyphosphatase of the cytosol and those of the vacuoles, mitochondrial membranes, and nuclei are presumably encoded by their own genes. Based on recent works, a preliminary classification of the yeast exopolyphosphatases is proposed.     

Compartmentalization of Spo11p in vegetative cells of yeast Saccharomyces cerevisiae

Homologous recombination is initiated in meiotic eukaryotic cells at DNA double-strand breaks, which are generated by several proteins, Spo11p playing a key role. The protein products of SPO11 orthologs are highly conserved, are found in most eukaryotes from plants to human, and are structurally similar to subunit A of archaeal DNA topoisomerase VI. Saccharomyces cerevisiae SPO11 is expressed in meiotic prophase I. Spo11p acts as topoisomerase II and is presumably active as a dimer. Experimental data on Spo11p compartmentalization in vegetative yeast cells are unavailable. The SPO11 coding region and its fragments were fused in frame with the egfp reporter and expressed in vegetative yeast cells. The Spo11p-EGFP fusion was localized in the nucleus, while cytoplasmic localization was observed for Spo11Δ-EGFP devoid of the 25 N-terminal residues. N-terminal Spo11p region 7–25 fused with EGFP ensured the nuclear targeting of the reporter protein and was assumed to harbor the nuclear localization signal.     

Compartmentalization of Spo11p in vegetative cells of yeast Saccharomyces cerevisiae

Double-stranded DNA breaks are currently thought to initiate homologous DNA recombination during meiosis. These breaks are mediated by several proteins, the key protein is Spol1p. Spo11 proteins being encoded by the highly conserved orthologs of SPO11 are present in most eukaryotes ranging from plants to man and are structurally similar to the subunit A of the archaea topoisomerase VI. The SPO11 of S. cerevisiae is currently known to be expressed during prophase I. It encodes a topoisomerase II that is apparently active as a dimer. Neither its localization in the native cells nor its nuclear localisation signals have been described in the literature. We report the expression of the coding region of SPO11 and its truncated variants C-terminally tagged by the egfp reporter in yeast. As judged by the EGFP fluorescence, the Spo11 p-EGFP fusion was localized in vegetative yeast nuclei whereas Spo11pdelta-EGFP lacking 25 N-terminal amino acids of Spollp was localized in cytoplasm. Nineteen N-terminal amino acids of Spo11p fused to EGFP made some reporter to be localized in the nucleus. Thus, we conclude that N-terminal part of Spo11p is a nuclear localization signal that is not specific for prophase I and is used to import proteins in vegetative yeast cells.     

Reconstruction of ethanol fermentation in permeabilized cells of the yeast Saccharomyces cerevisiae

Saccharomyces cerevisiae cells from a stationary culture were permeabilized with 1% toluene, 4% ethanol and 0.075% Triton X-100. Not only sugars but also ATP, NAD⁺, magnesium and inorganic phosphate must be simultaneously added to initiate the ethanol fermentation. The optimal pH for the fermentation was between 6.9 to 7.0. Sucrose was a better substrate than glucose. Ethanol fermentation was greatly stimulated by the addition of 1 mM arsenate. Under this condition, permeabilized cells continued to produce ethanol for more than one hour at the rate of 0.141 mmol ethanol/min/mg protein. Methanol inhibited the fermentation with intact cells but did not inhibit the one using permeabilized cells. In contrast, propanol inhibited fermentations both with intact and permeabilized cells.     

Different life strategies in genetic backgrounds of the Saccharomyces cerevisiae yeast cells

Changes in the natural environment require an organism to make constant adaptations enabling efficient use of environmental resources and ensuring its success in competition with other organisms. Such adaptations are expressed through various life strategies, largely determined by the rate of consumption and use of available resources, affecting the life-history traits and the related trade-offs. Allocation of available resources must take into consideration the costs of cell maintenance as well as reproduction. Given that carbon metabolism plays a crucial role in resource allocation, yeast living in different ecological niches show various life-history traits. There are a lot of data about life-history strategies in yeast living in various ecological niches; however, the question is whether different life strategies will be noted for yeast strains growing under strictly controlled conditions. Our studies based on three laboratory yeast strains representing different genetic backgrounds show that each of these strains has specified life strategies which are mainly determined by the glucose uptake rate and its intracellular usage. These results suggest that specific life strategies and related differences in the physiological and metabolic parameters of the cell are the key aspects that may explain various features of cells from different yeast strains, either industrial or laboratory.     

Sporulation in the budding yeast Saccharomyces cerevisiae

In response to nitrogen starvation in the presence of a poor carbon source, diploid cells of the yeast Saccharomyces cerevisiae undergo meiosis and package the haploid nuclei produced in meiosis into spores. The formation of spores requires an unusual cell division event in which daughter cells are formed within the cytoplasm of the mother cell. This process involves the de novo generation of two different cellular structures: novel membrane compartments within the cell cytoplasm that give rise to the spore plasma membrane and an extensive spore wall that protects the spore from environmental insults. This article summarizes what is known about the molecular mechanisms controlling spore assembly with particular attention to how constitutive cellular functions are modified to create novel behaviors during this developmental process. Key regulatory points on the sporulation pathway are also discussed as well as the possible role of sporulation in the natural ecology of S. cerevisiae.     

Sucrose inversion by gelatin-entrapped cells of yeast (Saccharomyces cerevisiae)

Summary Sucrose hydrolysis by invertase-active yeast cells (S. cerevisiae) entrapped in gelatin was investigated using different types of miniaturized reactors. The entrapped preparations showed the highest operational stability in a continuous stirred-tank reactor. The invertase activity of the entrapped preparation was found to be almost independent of the buffer concentration so that sucrose invermay be conducted in a non-buffered medium.     

Damage-induced recombination in the yeast Saccharomyces cerevisiae

Prokaryotic and eukaryotic cells have developed a network of DNA repair systems that restore genomic integrity following DNA damage from endogenous and exogenous genotoxic sources. One of the mechanisms used to repair damaged chromosomes is genetic recombination, in which information present as a second chromosomal copy is used to repair a damaged region of the genome. In this review, I summarized what is known about the molecular and cellular mechanisms by which various DNA-damaging agents induce recombination in yeast. The yeast Saccharomyces cerevisiae has served as an excellent model organism to study the induction of recombination. It has helped to define the basic phenomenology and to isolate the genes involved in the process. Given the evolutionary conservation of the various DNA repair systems in eukaryotes, it is likely that the knowledge gathered about induced recombination in yeast is applicable to mammalian cells and thus to humans. Many carcinogens are known to induce recombination and to cause chromosomal rearrangements. An understanding of the mechanisms, by which genotoxic agents cause increased levels of recombination will have important consequences for the treatment of cancer, and for the assessment of risks arising from exposure to genotoxic agents in humans.     

Acid excreting mutants of yeast Saccharomyces cerevisiae

Saccharomyces cerevisiae mutants acidifying glucose medium containing bromocresol purple were shown to excrete protons when placed in unbuffered water in the absence of any external carbon source. The mutants belong to 16 different complementation groups. Most of them do not grow on glycerol and the excreted protons are associated to particular sets of organic anions such as citrate, aconitate, succinate, fumarate or malate. These novel types of respiratory mutations seem to be located in genes operating in the Krebs or glyoxylate cycle.     

Properties of catalase activity in vegetative and sporulating cells of yeast Saccharomyces cerevisiae

Properties of catalase activities have been examined in the intact cells of early stationary phase and cells 3 hr after transfer to sporulation medium in Saccharomyces cerevisiae. The catalase activities of the two cells had a broad optimal pH from 6 to 8. Catalase activity in the intact cells increased throughout a 4-hr period of the observation following transfer to sporulation medium. Almost all the catalase activity in vegetative cells was lost by the treatment at 60 degrees C for 10 min. Catalase activities of both cells were inhibited by KCN, NaN3, o-phenanthroline, and PCMB. The catalase activity of the vegetative cells was slightly more inhibited and inactivated than that of the sporulating cells by the inhibitors and by the treatment with HCl or NaOH.     

Meiotic karyotype of the yeast Saccharomyces cerevisiae

A cytogenetic study of the meiotic chromosomes of the budding yeast Saccharomyces cerevisiae was undertaken by high resolution epifluorescence microscopy. Condensation of chromatin into separate chromosomes takes place during prophase I. At metaphase I, there are 16 separate and distinct bivalents which are roughly classified into three groups by morphological differences and DNA content.