Anin vitroassay for (1 → 6)-β-D-glucan synthesis inSaccharomyces cerevisiae

Antibody- Based Immunotherapy Combined With Antimycotic Drug TMP- SMX to Treat Infection With Paracoccidioides brasiliensis

Monoclonal antibodies (mAbs) are promising alternatives to treat infectious diseases, especially given their potential for applications in combination therapies with antimicrobial drugs to enhance the antifungal efficacy. Protection mediated by mAbs used to treat experimental paracoccidioidomycosis (PCM) has been demonstrated previously. Our aim in the present work was to characterize a monoclonal antibody (mAbF1.4) raised against a cell wall glycoconjugate fraction of Paracoccidioides spp. and to analyze its efficacy combined with trimethoprim-sulfamethoxazole (TMP/SMX) as treatment for experimental PCM. We demonstrated that the epitope recognized by mAbF1.4 is consistent with branched glucose residues present on a cell wall β-glucan polymer. In vitro, mAbF1.4 increased the phagocytic capacity and nitric oxide concentration induced by the macrophage cell line J774.1A, and this resulted in a significant reduction in the viability of the opsonophagocytized yeasts. In vivo, we detected a significant reduction in pulmonary fungal burdens of mice treated with mAbF1.4 in association with TMP/SMX, which correlated with increased pulmonary concentrations (determined by ELISA) of IFN- γ, TNF-α, IL-10 and IL-17. In parallel, we observed a decrease in IL-4, suggesting that the treatment was associated with a mixed Th1-Th17 type immune response. Histopathology of lung segments from mice receiving the combination therapy showed a significant reduction in granulomas, which were well-defined, and improved maintenance of lung architecture. These findings demonstrate that mAbF1.4 + TMP/SMX therapy is a promising approach to combat PCM as well as decrease disease sequelae and highlights the potential benefits of immune mediators in PCM combined immunotherapy.

Antifungal Activity Directed Toward the Cell Wall by 2-Cyclohexylidenhydrazo- 4-Phenyl-Thiazole Against Candida albicans

BACKGROUND

The increasing incidence of invasive forms of candidiasis and resistance to antifungal therapy leads us to seek new and more effective antifungal compounds.

OBJECTIVE

To investigate the antifungal activity and toxicity as well as to evaluate the potential targets of 2- cyclohexylidenhydrazo-4-phenyl-thiazole (CPT) in Candida albicans.

METHODS

The antifungal activity of CPT against the survival of C. albicans was investigated in Caenorhabditis elegans. Additionally, we determined the effect of CPT on the inhibition of C. albicans adhesion capacity to buccal epithelial cells (BECs), the toxicity of CPT in mammalian cells, and the potential targets of CPT in C. albicans.

RESULTS

CPT exhibited a minimum inhibitory concentration (MIC) value of 0.4-1.9 µg/mL. Furthermore, CPT at high concentrations (>60 x MIC) showed no or low toxicity in HepG2 cells and <1% haemolysis in human erythrocytes. In addition, CPT decreased the adhesion capacity of yeasts to the BECs and prolonged the survival of C. elegans infected with C. albicans. Analysis of CPT-treated cells showed that their cell wall was thinner than that of untreated cells, especially the glucan layer. We found that there was a significantly lower quantity of 1,3-β-D-glucan present in CPT-treated cells than that in untreated cells. Assays performed on several mutant strains showed that the MIC value of CPT was high for its antifungal activity on yeasts with defective 1,3-β-glucan synthase.

CONCLUSION

In conclusion, CPT appears to target the cell wall of C. albicans, exhibits low toxicity in mammalian cells, and prolongs the survival of C. elegans infected with C. albicans.

Phosphoric Metabolites Link Phosphate Import and Polysaccharide Biosynthesis for Candida albicans Cell Wall Maintenance

Candida species cause hundreds of thousands of invasive infections with high mortality each year. Developing novel antifungal agents is challenging due to the many similarities between fungal and human cells. Maintaining phosphate balance is essential for all organisms but is achieved completely differently by fungi and humans. A protein that imports phosphate into fungal cells, Pho84, is not present in humans and is required for normal cell wall stress resistance and cell wall integrity signaling in C. albicans. Nucleotide sugars, which are phosphate-containing building block molecules for construction of the cell wall, are diminished in cells lacking Pho84. Cell wall-constructing enzymes may be slowed by lack of these building blocks, in addition to being inhibited by drugs. Combined targeting of Pho84 and cell wall-constructing enzymes may provide a strategy for antifungal therapy by which two sequential steps of cell wall maintenance are blocked for greater potency.

The Candida albicans high-affinity phosphate transporter Pho84 is required for normal Target of Rapamycin (TOR) signaling, oxidative stress resistance, and virulence of this fungal pathogen. It also contributes to C. albicans’ tolerance of two antifungal drug classes, polyenes and echinocandins. Echinocandins inhibit biosynthesis of a major cell wall component, beta-1,3-glucan. Cells lacking Pho84 were hypersensitive to other forms of cell wall stress beyond echinocandin exposure, while their cell wall integrity signaling response was weak. Metabolomics experiments showed that levels of phosphoric intermediates, including nucleotides like ATP and nucleotide sugars, were low in pho84 mutant compared to wild-type cells recovering from phosphate starvation. Nonphosphoric precursors like nucleobases and nucleosides were elevated. Outer cell wall phosphomannan biosynthesis requires a nucleotide sugar, GDP-mannose. The nucleotide sugar UDP-glucose is the substrate of enzymes that synthesize two major structural cell wall polysaccharides, beta-1,3- and beta-1,6-glucan. Another nucleotide sugar, UDP-N-acetylglucosamine, is the substrate of chitin synthases which produce a stabilizing component of the intercellular septum and of lateral cell walls. Lack of Pho84 activity, and phosphate starvation, potentiated pharmacological or genetic perturbation of these enzymes. We posit that low substrate concentrations of beta-d-glucan- and chitin synthases, together with pharmacologic inhibition of their activity, diminish enzymatic reaction rates as well as the yield of their cell wall-stabilizing products. Phosphate import is not conserved between fungal and human cells, and humans do not synthesize beta-d-glucans or chitin. Hence, inhibiting these processes simultaneously could yield potent antifungal effects with low toxicity to humans.

The fungal cell wall as a target for the development of new antifungal therapies

In the past three decades invasive mycoses have globally emerged as a persistent source of healthcare-associated infections. The cell wall surrounding the fungal cell opposes the turgor pressure that otherwise could produce cell lysis. Thus, the cell wall is essential for maintaining fungal cell shape and integrity. Given that this structure is absent in host mammalian cells, it stands as an important target when developing selective compounds for the treatment of fungal infections. Consequently, treatment with echinocandins, a family of antifungal agents that specifically inhibits the biosynthesis of cell wall (1-3)β-D-glucan, has been established as an alternative and effective antifungal therapy. However, the existence of many pathogenic fungi resistant to single or multiple antifungal families, together with the limited arsenal of available antifungal compounds, critically affects the effectiveness of treatments against these life-threatening infections. Thus, new antifungal therapies are required. Here we review the fungal cell wall and its relevance in biotechnology as a target for the development of new antifungal compounds, disclosing the most promising cell wall inhibitors that are currently in experimental or clinical development for the treatment of some invasive mycoses.

β-(1→6)-D-glucan secreted during the optimised production of exopolysaccharides by Paecilomyces variotii has immunostimulatory activity

Paecilomyces variotii is a filamentous fungus that occurs worldwide in soil and decaying vegetation. Optimization of the fermentation process for exopolysaccharide (EPS) production from the fungus P. variotii, structure determination and immuno-stimulating activity of EPS were performed. Response surface methodology (RSM) coupled with central composite design (CCD) was used to optimize the physical and chemical factors required to produce EPS in submerged fermentation. Preliminary investigations to choose the three factors for the present work were made using a factorial experimental design. Glucose, ammonium nitrate (NH₄NO₃) and pH were used as variables for which, with constant temperature of 28 °C and agitation of 90 rpm, the optimal process parameters were determined as glucose values of 0.96%, NH₄NO₃ 0.26% and pH 8.0. The three parameters presented significant effects. In this condition of culture, the main composition of the isolated EPS was a linear β-(1 → 6)-linked-D-glucan, as determined by Nuclear Magnetic Resonance (NMR) and methylation analysis. This polysaccharide is a very unusual as an EPS from fungi, especially a filamentous fungus such as P. variotii. Murine peritoneal macrophages cultivated with β-glucan for 6 and 48 h showed an increase in TNF-α, IL-6 and nitric oxide release with increased polysaccharide concentrations. Therefore, we conclude that the β-(1 → 6)-linked-D-glucan produced in optimised conditions of P. variotii cultivation has an immune-stimulatory activity on murine macrophages.

Evidence for Proinflammatory β-1,6 Glucans in the Pneumocystis carinii Cell Wall

Inflammation is a major cause of respiratory impairment during Pneumocystis pneumonia. Studies support a significant role for cell wall β-glucans in stimulating inflammatory responses. Fungal β-glucans are comprised of d-glucose homopolymers containing β-1,3-linked glucose backbones with β-1,6-linked glucose side chains. Prior studies in Pneumocystis carinii have characterized β-1,3 glucan components of the organism. However, recent investigations in other organisms support important roles for β-1,6 glucans, predominantly in mediating host cellular activation. Accordingly, we sought to characterize β-1,6 glucans in the cell wall of Pneumocystis and to establish their activity in lung cell inflammation. Immune staining revealed specific β-1,6 localization in P. carinii cyst walls. Homology-based cloning facilitated characterization of a functional P. carinii kre6 (Pckre6) β-1,6 glucan synthase in Pneumocystis that, when expressed in kre6-deficient Saccharomyces cerevisiae, restored cell wall stability. Recently synthesized β-1,6 glucan synthase inhibitors decreased the ability of isolated P. carinii preparations to generate β-1,6 carbohydrate. In addition, isolated β-1,6 glucan fractions from Pneumocystis elicited vigorous tumor necrosis factor alpha (TNF-α) responses from macrophages. These inflammatory responses were significantly dampened by inhibition of host cell plasma membrane microdomain function. Together, these studies indicate that β-1,6 glucans are present in the P. carinii cell wall and contribute to lung cell inflammatory activation during infection.

A specific immunological method to detect and quantify bacterial 2-substituted (1,3)-β-D-glucan

Exopolysaccharides synthesized by lactic acid bacteria have prebiotic properties and contribute to the rheology and texture of fermented foods. Here, we have standardized an immunological method for the specific detection of 2-substituted (1,3)-β-D-glucans. The method allows direct detection and quantification of this exopolysaccharide in culture supernatants containing other mono- and poly-saccharides. Moreover, it allows specific detection of the biomolecules synthesized in vitro in enzymatic reactions. Thus, this method allows the fast identification of producing bacteria, as well as biochemical characterization of the glycosyltransferases responsible for their synthesis.

A novel fluorescence assay and catalytic properties of Crh1 and Crh2 yeast cell wall transglycosylases

A fluorescence assay was devised for the determination of transglycosylating activities of Crh1 and Crh2 yeast cell wall mannoproteins. Both proteins use chitin derivatives as donors and oligosaccharides derived from chitin, β-(1,3)-glucan and β-(1,6)-glucan as acceptors in vitro and in vivo.

Architecture and biosynthesis of the Saccharomyces cerevisiae cell wall

The wall gives a Saccharomyces cerevisiae cell its osmotic integrity; defines cell shape during budding growth, mating, sporulation, and pseudohypha formation; and presents adhesive glycoproteins to other yeast cells. The wall consists of β1,3- and β1,6-glucans, a small amount of chitin, and many different proteins that may bear N- and O-linked glycans and a glycolipid anchor. These components become cross-linked in various ways to form higher-order complexes. Wall composition and degree of cross-linking vary during growth and development and change in response to cell wall stress. This article reviews wall biogenesis in vegetative cells, covering the structure of wall components and how they are cross-linked; the biosynthesis of N- and O-linked glycans, glycosylphosphatidylinositol membrane anchors, β1,3- and β1,6-linked glucans, and chitin; the reactions that cross-link wall components; and the possible functions of enzymatic and nonenzymatic cell wall proteins.

Regulation of cell wall biogenesis in Saccharomyces cerevisiae: the cell wall integrity signaling pathway

The yeast cell wall is a strong, but elastic, structure that is essential not only for the maintenance of cell shape and integrity, but also for progression through the cell cycle. During growth and morphogenesis, and in response to environmental challenges, the cell wall is remodeled in a highly regulated and polarized manner, a process that is principally under the control of the cell wall integrity (CWI) signaling pathway. This pathway transmits wall stress signals from the cell surface to the Rho1 GTPase, which mobilizes a physiologic response through a variety of effectors. Activation of CWI signaling regulates the production of various carbohydrate polymers of the cell wall, as well as their polarized delivery to the site of cell wall remodeling. This review article centers on CWI signaling in Saccharomyces cerevisiae through the cell cycle and in response to cell wall stress. The interface of this signaling pathway with other pathways that contribute to the maintenance of cell wall integrity is also discussed.

Kre6 protein essential for yeast cell wall beta-1,6-glucan synthesis accumulates at sites of polarized growth

Saccharomyces cerevisiae Kre6 is a type II membrane protein with amino acid sequence homology with glycoside hydrolase and is essential for β-1,6-glucan synthesis as revealed by the mutant phenotype, but its biochemical function is still unknown. The localization of Kre6, determined by epitope tagging, is a matter of debate. We raised anti-Kre6 rabbit antiserum and examined the localization of Kre6 and its tagged protein by immunofluorescence microscopy, subcellular fractionation in sucrose density gradients, and immunoelectron microscopy. Integration of the results indicates that the majority of Kre6 is in the endoplasmic reticulum; however, a small but significant portion is also present in the secretory vesicle-like compartments and plasma membrane. Kre6 in the latter compartments is observed as strong signals that accumulate at the sites of polarized growth by immunofluorescence. The truncated Kre6 without the N-terminal 230-amino acid cytoplasmic region did not show this polarized accumulation and had a severe defect in β-1,6-glucan synthesis. This is the first evidence of a β-1,6-glucan-related protein showing the polarized membrane localization that correlates with its biological function.

Effect of beta-1,6-glucan inhibitors on the invasion process of Candida albicans: potential mechanism of their in vivo efficacy

Beta-1,6-glucan is a fungus-specific cell wall component that is essential for the retention of many cell wall proteins. We recently reported the discovery of a small molecule inhibitor of beta-1,6-glucan biosynthesis in yeasts. In the course of our study of its derivatives, we found a unique feature in their antifungal profile. D21-6076, one of these compounds, exhibited potent in vitro and in vivo antifungal activities against Candida glabrata. Interestingly, although it only weakly reduced the growth of Candida albicans in conventional media, it significantly prolonged the survival of mice infected by the pathogen. Biochemical evaluation of D21-6076 indicated that it inhibited beta-1,6-glucan synthesis of C. albicans, leading the cell wall proteins, which play a critical role in its virulence, to be released from the cell. Correspondingly, adhesion of C. albicans cells to mammalian cells and their hyphal elongation were strongly reduced by the drug treatment. The results of the experiment using an in vitro model of vaginal candidiasis showed that D21-6076 strongly inhibited the invasion process of C. albicans without a significant reduction in its growth in the medium. These evidences suggested that D21-6076 probably exhibited in vivo efficacy against C. albicans by inhibiting its invasion process.

Cell wall beta-(1,6)-glucan of Saccharomyces cerevisiae: structural characterization and in situ synthesis

Despite its essential role in the yeast cell wall, the exact composition of the beta-(1,6)-glucan component is not well characterized. While solubilizing the cell wall alkali-insoluble fraction from a wild type strain of Saccharomyces cerevisiae using a recombinant beta-(1,3)-glucanase followed by chromatographic characterization of the digest on an anion exchange column, we observed a soluble polymer that eluted at the end of the solvent gradient run. Further characterization indicated this soluble polymer to have a molecular mass of approximately 38 kDa and could be hydrolyzed only by beta-(1,6)-glucanase. Gas chromatography mass spectrometry and NMR ((1)H and (13)C) analyses confirmed it to be a beta-(1,6)-glucan polymer with, on average, branching at every fifth residue with one or two beta-(1,3)-linked glucose units in the side chain. This polymer peak was significantly reduced in the corresponding digests from mutants of the kre genes (kre9 and kre5) that are known to play a crucial role in the beta-(1,6)-glucan biosynthesis. In the current study, we have developed a biochemical assay wherein incubation of UDP-[(14)C]glucose with permeabilized S. cerevisiae yeasts resulted in the synthesis of a polymer chemically identical to the branched beta-(1,6)-glucan isolated from the cell wall. Using this assay, parameters essential for beta-(1,6)-glucan synthetic activity were defined.

KEG1/YFR042w Encodes a Novel Kre6-binding Endoplasmic Reticulum Membrane Protein Responsible for β-1,6-Glucan Synthesis in Saccharomyces cerevisiae

KEG1/YFR042w of Saccharomyces cerevisiae is an essential gene that encodes a 200-amino acid polypeptide with four predicted transmembrane domains. The green fluorescent protein- or Myc(6)-tagged Keg1 protein showed the typical characteristics of an integral membrane protein and was found in the endoplasmic reticulum by fluorescence imaging. Immunoprecipitation from the Triton X-100-solubilized cell lysate revealed that Keg1 binds to Kre6, which has been known to participate in beta-1,6-glucan synthesis. To analyze the essential function of Keg1 in more detail, we constructed temperature-sensitive mutant alleles by error-prone polymerase chain reaction. The keg1-1 mutant cells showed a common phenotype with Deltakre6 mutant including hypersensitivity to Calcofluor white, reduced sensitivity to the K1 killer toxin, and reduced content of beta-1,6-glucan in the cell wall. These results suggest that Keg1 and Kre6 have a cooperative role in beta-1,6-glucan synthesis in S. cerevisiae.

Central roles of small GTPases in the development of cell polarity in yeast and beyond

SUMMARY

The establishment of cell polarity is critical for the development of many organisms and for the function of many cell types. A large number of studies of diverse organisms from yeast to humans indicate that the conserved, small-molecular-weight GTPases function as key signaling proteins involved in cell polarization. The budding yeast Saccharomyces cerevisiae is a particularly attractive model because it displays pronounced cell polarity in response to intracellular and extracellular cues. Cells of S. cerevisiae undergo polarized growth during various phases of their life cycle, such as during vegetative growth, mating between haploid cells of opposite mating types, and filamentous growth upon deprivation of nutrition such as nitrogen. Substantial progress has been made in deciphering the molecular basis of cell polarity in budding yeast. In particular, it becomes increasingly clear how small GTPases regulate polarized cytoskeletal organization, cell wall assembly, and exocytosis at the molecular level and how these GTPases are regulated. In this review, we discuss the key signaling pathways that regulate cell polarization during the mitotic cell cycle and during mating.

Cell wall assembly in Saccharomyces cerevisiae

An extracellular matrix composed of a layered meshwork of beta-glucans, chitin, and mannoproteins encapsulates cells of the yeast Saccharomyces cerevisiae. This organelle determines cellular morphology and plays a critical role in maintaining cell integrity during cell growth and division, under stress conditions, upon cell fusion in mating, and in the durable ascospore cell wall. Here we assess recent progress in understanding the molecular biology and biochemistry of cell wall synthesis and its remodeling in S. cerevisiae. We then review the regulatory dynamics of cell wall assembly, an area where functional genomics offers new insights into the integration of cell wall growth and morphogenesis with a polarized secretory system that is under cell cycle and cell type program controls.

The structural basis for the serospecificity ofActinobacillus suisserogroup O:2

Actinobacillus suis is an important bacterial pathogen of healthly pigs. An O-antigen (lipopolysaccharide; LPS) serotyping system is being developed to study the prevalence and distribution of representative isolates from both healthy and diseased pigs. In a previous study, we reported that A. suis serogroup O:1 strains express LPS with a (1→6)-β-D-glucan O-antigen chain polysaccharide that is similar in structure to a key cell-wall component in yeasts, such as Saccharomyces cerevisiae and Candida albicans. This study describes the O-antigen polysaccharide chemical structure of an O:2 serogroup strain, A. suis H91-0380, which possesses a tetrasaccharide repeating block with the structure: →3)-β-D-Galp-(1→4)-[α-D-Galp-(1→6)]-β-D-Glcp-(1→6)-β-D-GlcpNAc-(1→. Studies have shown that A. suis serogroup O:2 strains are associated with severely diseased animals; therefore, work on the synthesis of a glycoconjugate vaccine employing O:2 O-antigen polysaccharide to vaccinate pigs against A. suis serogroup O:2 strains is currently underway.Key words: Actinobacillus suis, lipopolysaccharide, serogroup O:2, vaccine.

Cell wall construction inSaccharomyces cerevisiae

In this review, we discuss new insights in cell wall architecture and cell wall construction in the ascomycetous yeast Saccharomyces cerevisiae. Transcriptional profiling studies combined with biochemical work have provided ample evidence that the cell wall is a highly adaptable organelle. In particular, the protein population that is anchored to the stress-bearing polysaccharides of the cell wall, and forms the interface with the outside world, is highly diverse. This diversity is believed to play an important role in adaptation of the cell to environmental conditions, in growth mode and in survival. Cell wall construction is tightly controlled and strictly coordinated with progression of the cell cycle. This is reflected in the usage of specific cell wall proteins during consecutive phases of the cell cycle and in the recent discovery of a cell wall integrity checkpoint. When the cell is challenged with stress conditions that affect the cell wall, a specific transcriptional response is observed that includes the general stress response, the cell wall integrity pathway and the calcineurin pathway. This salvage mechanism includes increased expression of putative cell wall assemblases and some potential cross-linking cell wall proteins, and crucial changes in cell wall architecture. We discuss some more enzymes involved in cell wall construction and also potential inhibitors of these enzymes. Finally, we use both biochemical and genomic data to infer that the architectural principles used by S. cerevisiae to build its cell wall are also used by many other ascomycetous yeasts and also by some mycelial ascomycetous fungi.

Yapsins are a family of aspartyl proteases required for cell wall integrity in Saccharomyces cerevisiae

The yeast cell wall is a crucial extracellular organelle that protects the cell from lysis during environmental stress and morphogenesis. Here, we demonstrate that the yapsin family of five glycosylphosphatidylinositol-linked aspartyl proteases is required for cell wall integrity in Saccharomyces cerevisiae. Yapsin null mutants show hypersensitivity to cell wall perturbation, and both the yps1Delta2Delta mutant and the quintuple yapsin mutant (5ypsDelta) undergo osmoremedial cell lysis at 37 degrees C. The cell walls of both 5ypsDelta and yps1Delta2Delta mutants have decreased amounts of 1,3- and 1,6-beta-glucan. Although there is decreased incorporation of both 1,3- and 1,6-beta-glucan in the 5ypsDelta mutant in vivo, in vitro specific activity of both 1,3- and 1,6-beta-glucan synthesis is similar to wild type, indicating that the yapsins affect processes downstream of glucan synthesis and that the yapsins may be involved in the incorporation or retention of cell wall glucan. Presumably as a response to the significant alterations in cell wall composition, the cell wall integrity mitogen-activated kinase signaling cascade (PKC1-MPK pathway) is basally active in 5ypsDelta. YPS1 expression is induced during cell wall stress and remodeling in a PKC1-MPK1-dependent manner, indicating that Yps1p is a direct, and important, output of the cell wall integrity response. The Candida albicans (SAP9) and Candida glabrata (CgYPS1) homologues of YPS1 complement the phenotypes of the yps1Delta mutant. Taken together, these data indicate that the yapsins play an important role in glucan homeostasis in S. cerevisiae and that yapsin homologues may play a similar role in the pathogenic yeasts C. albicans and C. glabrata.

Features and functions of covalently linked proteins in fungal cell walls

The cell walls of many ascomycetous yeasts consist of an internal network of stress-bearing polysaccharides, which serve as a scaffold for a dense external layer of glycoproteins. GPI-modified proteins are the most abundant cell wall proteins and often display a common organization. Their C-terminus can link them covalently to the polysaccharide network, they possess an internal serine- and threonine-rich spacer domain, and the N-terminal region contains a functional domain. Other proteins bind to the polysaccharide network through a mild-alkali-sensitive linkage. Many cell wall proteins are carbohydrate/glycan-modifying enzymes; adhesion proteins are prominent; proteins involved in iron uptake are present, and also specialized proteins that probably help the fungus to survive in its natural environment. The protein composition of the cell wall depends on environmental conditions and developmental stage. We present evidence that the cell wall of mycelial species of the Ascomycotina is similarly organized and contains glycoproteins with comparable functions.

Cell wall integrity signaling in Saccharomyces cerevisiae

The yeast cell wall is a highly dynamic structure that is responsible for protecting the cell from rapid changes in external osmotic potential. The wall is also critical for cell expansion during growth and morphogenesis. This review discusses recent advances in understanding the various signal transduction pathways that allow cells to monitor the state of the cell wall and respond to environmental challenges to this structure. The cell wall integrity signaling pathway controlled by the small G-protein Rho1 is principally responsible for orchestrating changes to the cell wall periodically through the cell cycle and in response to various forms of cell wall stress. This signaling pathway acts through direct control of wall biosynthetic enzymes, transcriptional regulation of cell wall-related genes, and polarization of the actin cytoskeleton. However, additional signaling pathways interface both with the cell wall integrity signaling pathway and with the actin cytoskeleton to coordinate polarized secretion with cell wall expansion. These include Ca(2+) signaling, phosphatidylinositide signaling at the plasma membrane, sphingoid base signaling through the Pkh1 and -2 protein kinases, Tor kinase signaling, and pathways controlled by the Rho3, Rho4, and Cdc42 G-proteins.

Current awareness on yeast

In order to keep subscribers up‐to‐date with the latest developments in their field, this current awareness service is provided by John Wiley & Sons and contains newly‐published material on yeasts. Each bibliography is divided into 10 sections. 1 Books, Reviews & Symposia; 2 General; 3 Biochemistry; 4 Biotechnology; 5 Cell Biology; 6 Gene Expression; 7 Genetics; 8 Physiology; 9 Medical Mycology; 10 Recombinant DNA Technology. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted. (4 weeks journals ‐ search completed 10th. Nov. 2004)