Risk factors for keratoconus progression after treatment by accelerated cross-linking (A-CXL): A prospective 24-month study

PURPOSE

Identification of potential predictive factors for keratoconus progression after treatment by accelerated Cross-linking (A-CXL) SECONDARY OBJECTIVES: Evaluation of clinical and topographic outcomes for two years following accelerated cross-linking treatment for progressive keratoconus including: best spectacle corrected visual acuity (BSCVA), thinnest pachymetry, maximum keratometry (Kmax), cylinder.

STUDY

Prospective, interventional, monocentric study. SITE: Metz-Thionville Regional Medical Center, Lorraine University, Mercy Hospital, Metz, France.

PATIENTS AND METHODS

We included 82 eyes of 60 patients between March 2014 and June 2016 who underwent accelerated corneal cross-linking (A-CXL) with epithelial debridement for progressive keratoconus, with a minimum follow-up of 2 years. A complete clinical evaluation and corneal topography were performed before cross-linking, and subsequently at 6, 12 and 24 months post-procedure. The following parameters were monitored during follow-up: best spectacle corrected visual acuity (BSCVA), minimal pachymetry, maximum keratometry (Kmax), mean anterior and posterior curvatures, maximum posterior curvature, presence of optical aberrations, subdivided into spherical aberration, coma, astigmatism, higher order optical aberrations and residual optical aberrations. After a 2-year follow-up, two groups, defined as "responders" and "non-responders" to treatment, were separated for analysis, and their initial characteristics were compared.

RESULTS

Data for 82 eyes of 60 patients with progressive keratoconus with a mean age of 24±7 years were studied. Fourteen eyes (17.1%) showed signs of progression after treatment by A-CXL (non-responders), and 68 eyes (82.9%) showed stabilization of the disease (responders). Characteristics of non-responding eyes after A-CXL included a younger mean age (20±5 vs. 25±7 years) (P=0.04) and a lower initial mean BCVA for non-responders of 0.44±0.16 logMAR vs. 0.29±0.19 logMAR (P=0.03). Non-responders also had a higher mean maximal posterior curvature (AKB) of -10.84±1.72D vs. -9.46± 1.12D (P=0.03). They also showed more higher order optical aberrations (3.84±1.72D vs. 2.4±1.02D; P=0.01), including coma (3.85±1.81D vs. 2.1±1.01D; P=0.03) and more residual aberrations than responders (1.05±0.44D vs. 0.45±0.6D; P=0.005). No significant differences were found between responders and non-responders for the other parameters in our study.

CONCLUSION

Eyes with progressive keratoconus who did not respond to A-CXL treatment were the most aggressive cases in the youngest patients, with highest maximum corneal curvatures and most pronounced optical aberrations. These patients should be informed in advance of the high risk of non-response to A-CXL treatment, and of the potential need for additional treatment in the future.

Exogenous application of a lipid transfer protein-jasmonic acid complex induces protection of grapevine towards infection by Botrytis cinerea

Type I plant lipid transfer proteins (LTPs) are small, basic, cystein-rich proteins involved in plant defense mechanisms. Five type I LTPs isoforms, named VvLTP1, 2, 3, 4 and 5 (Vitis vinifera lipid transfer proteins 1-5) were purified to homogeneity from the culture media of 41B grapevine cell suspension. The full sequence of isoforms 1, 3, 4 and 5 could be determined from mass spectrometry measurements of the enzymatically hydrolyzed proteins and from available VvLTP sequences. Phylogenetic analysis revealed that these proteins form two subgroups, one with isoforms 1 and 4, and the second one with isoforms 3 and 5. The ability of the three most abundant ones (VvLTP1, 4 and 3) to interact with jasmonic acid (JA) was tested by fluorometric studies, showing that VvLTP4 was the most efficient to interact with this oxylipin. Exogenous application of the VvLTP4-JA complex on grapevine plantlets induced a high level (80.3+/-10.05%) of tolerance towards Botrytis cinerea, as compared with control plants (18.65+/-12.13%); whereas plants treated with JA or VvLTP4 alone exhibited a lower protection level (31.04+/-9.72% and 45.52+/-7.51% of protection, respectively). The results are discussed in the context of grapevine defense mechanisms.

Direct microcontact printing of oligonucleotides for biochip applications

Background

A critical step in the fabrication of biochips is the controlled placement of probes molecules on solid surfaces. This is currently performed by sequential deposition of probes on a target surface with split or solid pins. In this article, we present a cost-effective procedure namely microcontact printing using stamps, for a parallel deposition of probes applicable for manufacturing biochips.

Results

Contrary to a previous work, we showed that the stamps tailored with an elastomeric poly(dimethylsiloxane) material did not require any surface modification to be able to adsorb oligonucleotides or PCR products. The adsorbed DNA molecules are subsequently printed efficiently on a target surface with high sub-micron resolution. Secondly, we showed that successive stamping is characterized by an exponential decay of the amount of transferred DNA molecules to the surface up the 4^th print, then followed by a second regime of transfer that was dependent on the contact time and which resulted in reduced quality of the features. Thus, while consecutive stamping was possible, this procedure turned out to be less reproducible and more time consuming than simply re-inking the stamps between each print. Thirdly, we showed that the hybridization signals on arrays made by microcontact printing were 5 to 10-times higher than those made by conventional spotting methods. Finally, we demonstrated the validity of this microcontact printing method in manufacturing oligonucleotides arrays for mutations recognition in a yeast gene.

Conclusion

The microcontact printing can be considered as a new potential technology platform to pattern DNA microarrays that may have significant advantages over the conventional spotting technologies as it is easy to implement, it uses low cost material to make the stamp, and the arrays made by this technology are 10-times more sensitive in term of hybridization signals than those manufactured by conventional spotting technology.

Influence of pH on complexing of model beta-d-glucans with zearalenone

Previous studies have shown that isolated beta-(1,3 and 1,6)-D-glucans and related alkali-extracted fractions from the cell wall of Saccharomyces cerevisiae are able to complex with zearalenone in vitro (affinity up to 50%) and thus may reduce the bioavailability of toxins in the digestive tract. The complexation mechanisms involve cooperative interaction between the two chemical entities that can be computed by Hill's model. Various linear or branched soluble or insoluble beta-D-glucans were evaluated to elucidate their roles in the adsorption mechanisms under three pH conditions (3.0, 6.0, and 8.0) found in the digestive tract. A constant quantity of each beta-D-glucans (1 mg/ml) was mixed at 39 degrees C with increasing amounts of zearalenone (2 to 100 microg/ml), and the amount of bound toxin was measured. Acidic and neutral conditions gave the highest affinity rates (64 to 77%) by beta-(1,3)-D-glucans, whereas alkaline conditions decreased adsorption except when beta-(1,6)-D-glucan side chains were branched on beta-(1,3)-D-glucans. Alkaline conditions appear to impede the active three dimensional conformation of beta-D-glucans and favor single helix and/or random coil structures. Study of the equilibrium between beta-D-glucan-bound and free toxins revealed that two types of chemical interactions occur during toxin complexation with beta-D-glucans, identified as weak chemical linkages such as hydrogen and van der Waals bonds.

Combinatorial control by the protein kinases PKA, PHO85 and SNF1 of transcriptional induction of the Saccharomyces cerevisiae GSY2 gene at the diauxic shift

Genes involved in storage carbohydrate metabolism are coordinately induced when yeast cells are subjected to conditions of stress, or when they exit the exponential growth phase on glucose. We show that the STress Responsive Elements (STREs) present in the promoter of GSY2 are essential for gene activation under conditions of stress, but dispensable for gene induction and glycogen accumulation at the diauxic shift on glucose. Using serial promoter deletion, we found that the latter induction could not be attributed to a single cis -regulatory sequence, and present evidence that this mechanism depends on combinatorial transcriptional control by signalling pathways involving the protein kinases Pho85, Snf1 and PKA. Two contiguous regions upstream of the GSY2 coding region are necessary for negative control by the cyclin-dependent protein kinase Pho85, one of which is a 14-bp G/C-rich sequence. Positive control by Snf1 is mediated by Mig1p, which acts indirectly on the distal part of the GSY2 promoter. The PKA pathway has the most pronounced effect on GSY2, since transcription of this gene is almost completely abolished in an ira1ira2 mutant strain in which PKA is hyperactive. The potent negative effect of PKA is dependent upon a branched pathway involving the transcription factors Msn2/Msn4p and Sok2p. The SOK2 branch was found to be effective only under conditions of high PKA activity, as in a ira1ira2 mutant, and this effect was independent of Msn2/4p. The Msn2/4p branch, on the other hand, positively controls GSY2 expression directly through the STREs, and indirectly via a factor that still remains to be discovered. In summary, this study shows that the transcription of GSY2 is regulated by several different signalling pathways which reflect the numerous factors that influence glycogen synthesis in yeast, and suggests that the PKA pathway must be deactivated to allow gene induction at the diauxic shift.

Adsorption of Zearalenone by beta-D-glucans in the Saccharomyces cerevisiae cell wall

Cell walls of yeasts and bacteria are able to complex with mycotoxins and limit their bioavailability in the digestive tract when these yeasts and bacteria are given as feed additives to animals. To identify the component(s) of the yeast cell wall and the chemical interaction(s) involved in complex formation with zearalenone, four strains of Saccharomyces cerevisiae differing in their cell wall glucan and mannan content were tested. Laboratory strains wt292, fks1, and mnn9 were compared with industrial S. cerevisiae strain sc1026. The complex-forming capacity of the yeast cell walls was determined in vitro by modelling the plots of amount of toxin bound versus amount of toxin added using Hill's model. A cooperative relationship between toxin and adsorbent was shown, and a correlation between the amount of beta-D-glucans in cell walls and complex-forming efficacy was revealed (R2 = 0.889). Cell walls of strains wt292 and mnn9, which have higher levels of beta-D-glucans, were able to complex larger amounts of zearalenone, with higher association constants and higher affinity rates than those of the fks1 and sc1026 strains. The high chitin content in strains mnn9 and fks1 increased the alkali insolubility of beta-D-glucans from isolated cell walls and decreased the flexibility of these cell walls, which restricted access of zearalenone to the chemical sites of the beta-D-glucans involved in complex formation. The strains with high chitin content thus had a lower complex-forming capacity than expected based on their beta-D-glucans content. Cooperativity and the three-dimensional structure of beta-D-glucans indicate that weak noncovalent bonds are involved in the complex-forming mechanisms associated with zearalenone. The chemical interactions between beta-D-glucans and zearalenone are therefore more of an adsorption type than a binding type.

[Autoantibodies and anti-factor VIII and Chlamydia pneumoniae infection]

We report the case of a 64-year-old man without hemorrhagic history experiencing epistaxis. The standard hemostasis assessment including prothrombin index, activated partial thromboplastin time (APTT) and platelet count found an isolated abnormal APTT (105 sec vs 33 sec). Therefore, coagulation factors were explored. An acquired factor VIII deficiency (5%) with anti-FVIII antibody (4.5 Bethesda unit.mL-1) was recognised. This anti-FVIII antibody was related to a Chlamydia pneumoniae pulmonary infection. Treatment consisted of: i) Four successive anterior packing and activated factor VII infusion (Novoseven); ii) steroids injection and bi-antibiotherapy. The time course of the epistaxis was favourable under treatment.

[Coronary angioplasty in the acute phase of myocardial infarction in a low-volume center]

The efficacy of coronary angioplasty in the treatment of acute myocardial infarction was assessed in a low volume centre. Between January 1994 and May 1999, 148 consecutive patients (mean age 59 years, 81% men) with acute myocardial infarction, admitted within 12 hours, were included in this retrospective analysis. On admission, 14% of patients were in cardiogenic shock. The average time between the onset of chest pain and arrival at hospital was 244 +/- 183 mins. Reperfusion (TIMI 3 flow) was obtained on average 111 +/- 60 mins after arrival at hospital and 81 mins after informing the on-call team. After angioplasty, residual stenosis < 50% was obtained in 91% of cases. TIMI 3 flow was obtained in 85% of cases (TIMI 2 + 3 in 93% of cases). Over the years, the delay before treatment decreased and the results of angioplasty improved. In the last 79 patients, residual stenosis < 50% was obtained in 95% of cases, TIMI 3 flow in 87% of cases (TIMI 2 + 3 in 97% of cases). The stenting rate increased from 16% before 1997 to 61% thereafter. The hospital mortality was 4%. Direct or salvage angioplasty in the first 12 hours of myocardial infarction in some low volume centres may be carried out safely with intervention times and success rates comparable to those reported in the literature.

Saccharomyces cerevisiae YCRO17c/CWH43 encodes a putative sensor/transporter protein upstream of the BCK2 branch of the PKC1-dependent cell wall integrity pathway

The Saccharomyces cerevisiae cwh43-2 mutant, originally isolated for its Calcofluor white hypersensitivity, displays several cell wall defects similar to mutants in the PKC1-MPK1 pathway, including a growth defect and increased release of beta-1,6-glucan and beta-glucosylated proteins into the growth medium at increased temperatures. The cloning of CWH43 showed that it corresponds to YCR017c and encodes a protein with 14-16 transmembrane segments containing several putative phosphorylation and glycosylation sites. The N-terminal part of the amino acid sequence of Cwh43p shows 40% similarity with the mammalian FRAG1, a membrane protein that activates the fibroblast growth factor receptor of rat osteosarcoma (FGFR2-ROS) and with protein sequences of four uncharacterized ORFs from Caenorhabditis elegans and one from Drosophila melanogaster. The C-terminus of Cwh43p shows low similarities with a xylose permease of Bacillus megaterium and with putative sugar transporter from D. melanogaster, and has 52% similarity with a protein sequence from a Schizosaccharomyces pombe cDNA. A Cwh43-GFP fusion protein suggested a plasma membrane localization, although localization to the internal structure of the cells could not be excluded, and it concentrates to the bud tip of small budded cells and to the neck of dividing cells. Deletion of CWH43 resulted in cell wall defects less pronounced than those of the cwh43-2 mutant. This allele-specific phenotype appears to be due to a G-R substitution at position 57 in a highly conserved region of the protein. Genetic analysis places CWH43 upstream of the BCK2 branch of the PKC1 signalling pathway, since cwh43 mutations were synthetic lethal with pkc1 deletion, whereas the cwh43 defects could be rescued by overexpression of BCK2 and not by high-copy-number expression of genes encoding downstream proteins of the PKC1 pathway However, unlike BCK2, whose disruption in a cln3 mutant resulted in growth arrest in G(1), no growth defect was observed in a double cwh43 cln3 mutants. Taken together, it is proposed that CWH43 encodes a protein with putative sensor and transporter domains acting in parallel to the main PKC1-dependent cell wall integrity pathway, and that this gene has evolved into two distinct genes in higher eukaryotes.

Rheological and small-angle neutron scattering studies of aqueous solutions of branched PEO-PPO-PEO copolymers

Tetronic 908 is a four-branched copolymer comprised of polyethylene oxide (PEO) and polypropylene oxide (PPO) blocks fixed on an aliphatic diamine. In aqueous solution, this polymer has an amphiphilic character due to the difference in PEO and PPO solubilities with increase in temperature. This system presents interesting rheological properties depending on the polymer concentration in solution and temperature. At low temperatures and/or concentrations, the solution behaves as a Newtonian fluid. For a weight percentage p comprised between 2% and 22%, the viscosity of the solution goes through a maximum. Small-angle neutron scattering experiments show that the increase in viscosity is due to progressive aggregation of chains. For weight percentages higher than p=22%, the viscosity of the system diverges and the mixture becomes gel-like. In fact, spectromechanical measurements show that the solution behaves as an entangled polymer with a high relaxation time in the flow zone. Small-angle neutron scattering (SANS) studies of the same solution reveal the presence of several peaks indicating that the micelles are organized in a cubic structure. We have developed a model that suitably describes the SANS curves of this system in the region where micelles are formed. Our model considers that micelles are trilayered spherical entities that coexist with unimers by obeying an equilibrium reaction. Moreover, it allows the calculation of several parameters such as the volume fraction of micelles, their size, and composition. The evolution of these parameters with temperature and polymer concentration is detailed. Comparisons with literature models are presented and discussed. This compilation of results has permitted the establishment of precise relations between the structure of this polymer in solution and its rheological properties.

Reserve carbohydrates metabolism in the yeast Saccharomyces cerevisiae

Glycogen and trehalose are the two glucose stores of yeast cells. The large variations in the cell content of these two compounds in response to different environmental changes indicate that their metabolism is controlled by complex regulatory systems. In this review we present information on the regulation of the activity of the enzymes implicated in the pathways of synthesis and degradation of glycogen and trehalose as well as on the transcriptional control of the genes encoding them. cAMP and the protein kinases Snf1 and Pho85 appear as major actors in this regulation. From a metabolic point of view, glucose-6-phosphate seems the major effector in the net synthesis of glycogen and trehalose. We discuss also the implication of the recently elucidated TOR-dependent nutrient signalling pathway in the control of the yeast glucose stores and its integration in growth and cell division. The unexpected roles of glycogen and trehalose found in the control of glycolytic flux, stress responses and energy stores for the budding process, demonstrate that their presence confers survival and reproductive advantages to the cell. The findings discussed provide for the first time a teleonomic value for the presence of two different glucose stores in the yeast cell.

A Light Scattering Study of the Association of Hydrophobically alpha- and alpha,omega-End-capped Poly(ethylene oxide) in Water

Several hydrophobically alpha- and alpha,omega-end-capped poly(ethylene oxide) polymers were studied by light scattering below and above their critical association concentration, in order to understand their association mechanisms. In the case of monofunctionalized PEO, a one-step closed association model well fits the experimental data, with a limit number of aggregation of about 30, consistent with other experimental data and a theoretical approach. In the case of difunctionalized PEO, a good description of the experimental data is obtained by assuming a two-step association process: at low concentration, the formation of "flower-like" micelles is well described by a closed association model, whereas at higher concentration, the progressive bridging of these "flowers" can be modeled by an open association. Copyright 2000 Academic Press.

Trehalose reserve in Saccharomyces cerevisiae: phenomenon of transport, accumulation and role in cell viability

Strains of Saccharomyces cerevisiae deleted for TPS1 encoding trehalose-6-phosphate synthase still accumulate trehalose when harbouring a functional MAL locus. We demonstrate that this accumulation results from an active uptake of trehalose present in the 'yeast extract' used to make the enriched culture media and that no accumulation is observed in mineral media. The uptake of trehalose was shown to be mediated by the alpha-glucoside transporter encoded by AGT1, the expression of which is linked to the presence of a functional MAL locus. Deletion of this gene in a MAL+ tps1 mutant abolished trehalose accumulation on a maltose or galactose mineral medium. However, small amounts of disaccharide were still detected in a agt1 tps1 double mutant when the medium was supplemented with 10 g trehalose l(-1), indicating the existence of a non-concentrative low-affinity sugar transporter. The presence of the high-affinity trehalose permease allowed us to investigate the effect of increasing exogenous trehalose from 0 to 10 g(-1) on intracellular accumulation. A maximum of ca. 10% (wt/wt dry cells) trehalose was attained in the presence of only 1 g l(-1) of disaccharide in the medium. The capability to monitor the intracellular content of trehalose by varying its extracellular concentration, independent of genetic alterations of the trehalose metabolic machinery, allowed the remarkable contribution of this molecule in stress tolerance to be demonstrated, as the higher the trehalose content, the longer the cell survival to a severe heat shock and to glucose starvation.

Medium-chain fatty acids affect citrinin production in the filamentous fungus Monascus ruber

During submerged culture in the presence of glucose and glutamate, the filamentous fungus Monascus ruber produces water-soluble red pigments together with citrinin, a mycotoxin with nephrotoxic and hepatoxic effects on animals. Analysis of the (13)C-pigment molecules from mycelia cultivated with [1-(13)C]-, [2-(13)C]-, or [1, 2-(13)C]acetate by (13)C nuclear magnetic resonance indicated that the biosynthesis of the red pigments used both the polyketide pathway, to generate the chromophore structure, and the fatty acid synthesis pathway, to produce a medium-chain fatty acid (octanoic acid) which was then bound to the chromophore by a trans-esterification reaction. Hence, to enhance pigment production, we tried to short-circuit the de novo synthesis of medium-chain fatty acids by adding them to the culture broth. Of fatty acids with carbon chains ranging from 6 to 18 carbon atoms, only octanoic acid showed a 30 to 50% stimulation of red pigment production, by a mechanism which, in contrast to expectation, did not involve its direct trans-esterification on the chromophore backbone. However, the medium- and long-chain fatty acids tested were readily assimilated by the fungus, and in the case of fatty acids ranging from 8 to 12 carbon atoms, 30 to 40% of their initial amount transiently accumulated in the growth medium in the form of the corresponding methylketone 1 carbon unit shorter. Very interestingly, these fatty acids or their corresponding methylketones caused a strong reduction in, or even a complete inhibition of, citrinin production by M. ruber when they were added to the medium. Several data indicated that this effect could be due to the degradation of the newly synthesized citrinin (or an intermediate in the citrinin pathway) by hydrogen peroxide resulting from peroxisome proliferation induced by medium-chain fatty acids or methylketones.

STRE- and cAMP-independent transcriptional induction of Saccharomyces cerevisiae GSY2 encoding glycogen synthase during diauxic growth on glucose

It has been shown that the so-called stationary phase GSY2 gene encoding glycogen synthase was induced as the cells left the exponential phase of growth, while glucose and all other nutrients were still plentiful in the medium (Parrou et al., 1999). Since this effect was essentially controlled at the transcriptional level, we looked for the cis- and trans-acting elements required for this specific growth-related genetic event. We demonstrated that mutations of the HAP2/3/4 binding site and of the two STress-Responsive cis-Elements (STRE) did not abolish the early induction of GSY2, although the latter mutation led to a 20-fold drop in the transcriptional activity of the promoter, as determined from lacZ gene fusions. Insertion of a DNA fragment (from -390 to -167 bp, relative to the ATG) of the promoter lacking the two STREs, upstream to the TATA box of a CYC1-lacZ fusion gene, allowed this reporter gene to be induced with a kinetic similar to that of GSY2-lacZ. Mutations in BCY1, which results in a hyperactive protein kinase A, did not alleviate the early induction, while causing a five- to 10-fold reduction in the transcriptional activity of GSY2. In addition, the repressive effect of protein kinase A was quantitatively conserved when both STREs were mutated in GSY2 promoter, indicating that the negative control of gene expression by the RAS-cAMP signalling pathway does not act solely through STREs. Taken together, these results are indicative of an active process that couples growth control to dynamic glucose consumption.

Adsorption of Telechelic Poly(ethylene oxide) on Colloids: Influence on Colloid Stability

Adsorption of telechelic polymers (hydrophobically end-capped poly(ethylene oxide)) on charged colloidal particles modifies the characteristics of the electrical double layer. These interfaces were found to be able to protect colloids against aggregation or to induce colloid destabilization depending on the molecular weight and type of surface coating. Colloid stability is observed when the polymer layer is thinner than the electrical double layer and when the adsorbed polymer adopts a tethered brush structure. Aggregation of coated latex particles induced by formation of interparticle polymer links is observed when (i) the distance of the random walk of the dangling paraffinic end group is larger than the thickness of the electrical double layer and (ii) the adsorbed polymer brush adopts a loopy structure. Aggregation is attributed to adsorption of hydrophobic end chains on two different latex particles. Copyright 1999 Academic Press.

AGT1, encoding an alpha-glucoside transporter involved in uptake and intracellular accumulation of trehalose in Saccharomyces cerevisiae

The trehalose content in Saccharomyces cerevisiae can be significantly manipulated by including trehalose at an appropriate level in the growth medium. Its uptake is largely dependent on the expression of AGT1, which encodes an alpha-glucoside transporter. The trehalose found in a tps1 mutant of trehalose synthase may therefore largely reflect its uptake from the enriched medium that was employed.

Dynamic responses of reserve carbohydrate metabolism under carbon and nitrogen limitations in Saccharomyces cerevisiae

The dynamic responses of reserve carbohydrates with respect to shortage of either carbon or nitrogen source was studied to obtain a sound basis for further investigations devoted to the characterization of mechanisms by which the yeast Saccharomyces cerevisiae can cope with nutrient limitation during growth. This study was carried out in well-controlled bioreactors which allow accurate monitoring of growth and frequent sampling without disturbing the culture. Under glucose limitation, genes involved in glycogen and trehalose biosynthesis (GLG1, GSY1, GSY2, GAC1, GLC3, TPS1), in their degradation (GPH1, NTHI), and the typical stress-responsive CTT1 gene were coordinately induced in parallel with glycogen, when the growth has left the pure exponential phase and while glucose was still plentiful in the medium. Trehalose accumulation was delayed until the diauxic shift, although TPS1 was induced much earlier, due to hydrolysis of trehalose by high trehalase activity. In contrast, under nitrogen limitation, both glycogen and trehalose began to accumulate at the precise time when the nitrogen source was exhausted from the medium, coincidentally with the transcriptional activation of genes involved in their metabolism. While this response to nitrogen starvation was likely mediated by the stress-responsive elements (STREs) in the promoter of these genes, we found that these elements were not responsible for the co-induction of genes involved in reserve carbohydrate metabolism during glucose limitation, since GLG1, which does not contain any STRE, was coordinately induced with GSY2 and TPS1.

A new method for quantitative determination of polysaccharides in the yeast cell wall. Application to the cell wall defective mutants of Saccharomyces cerevisiae

A reliable acid hydrolysis method for quantitative determination of the proportion of beta-glucan, mannan and chitin in Saccharomyces cerevisiae cell wall is reported together with a simple extraction procedure to quantify within a standard error of less than 2% the proportion of the wall per gram of cell dry mass. This method is an optimized version of Saeman's procedure based on sulfuric acid hydrolysis of complex polysaccharides. It resulted in an almost complete release of glucose, mannose and glucosamine residues from cell wall polysaccharides. After complete removal of sulfate ions by precipitation with barium hydroxide, the liberated monosaccharides were separated and quantified by high performance anion-exchange chromatography with pulsed amperometric detection. The superiority of this method over the hydrolysis in either trifluoroacetic or hydrochloric acid resides in its higher efficiency regarding the release of glucose from beta 1,6-glucan and of glucosamine from chitin. The sulfuric acid method was successfully applied to determine the beta-glucan, mannan and chitin contents in cell walls of genetically well-characterized yeast mutants defective in cell wall biosynthesis, and in Schizosaccharomyces pombe cell walls. The simplicity and reliability of this procedure make it the method of choice for the characterization of cell walls from S. cerevisiae mutants generated in the EUROFAN programme, as well as for other pharmacological and biotechnological applications.

High resolution capillary electrophoretic separation of oligonucleotides in low-viscosity, hydrophobically end-capped polyethylene oxide with cubic order

A triblock self-associating polymer with the structure n-dodecane-poly(ethylene oxide)-n-dodecane and a very low polydispersity has been used as a matrix to separate a sample of single-stranded oligonucleotides containing Pd(A)25-30 and Pd(A)40-60. Above a concentration of 4%, this associative polymer forms a micellar network with cubic order and a well-defined micellar spacing, in which the dodecane micellar cores are bridged by polyoxyethylene segments. This medium combines a low viscosity with excellent resolution of oligonucleotides. This work confirms that associative polymers are potentially powerful media for separation in capillary electrophoresis, and argues in favor of the use of monodisperse products presenting a high-order in the physical gel state.

A rapid and reliable method for metabolite extraction in yeast using boiling buffered ethanol

A simple and reliable method for the efficient inactivation of metabolism and for quantitative metabolite extraction from yeast cells is presented. It is based on the use of a boiling solution made of 75% ethanol (volume/final volume) buffered with 70 mM-Hepes (final concentration), pH 7.5, to guarantee the stability throughout the whole procedure of a large variety of metabolites, including all glycolytic intermediates, nucleotides, pyridine nucleotides and organic acids compounds. The extraction is fast, requiring only 3 min incubation of yeast cells in the ethanol-buffered mixture maintained at 80 degrees C. It can be carried out either directly by spraying the cells into the boiling mixture, or after quenching the whole culture in 60% methanol kept at -40 degrees C. Extracts are subsequently concentrated by evaporation under partial vacuum and the residue is resuspended in a small volume of water. This concentration step and the use of a highly sensitive analytical method allow us to quantify metabolites in less than 10 mg dry weight cells. This method, which can be applied to other fungi, could be very helpful for the determination of true metabolites in mutants generated through the EUROFAN programme and for metabolic flux analysis.

Physiological and morphological effects of genetic alterations leading to a reduced synthesis of UDP-glucose in Saccharomyces cerevisiae

Yeast cells lacking UDP-Glc pyrophosphorylase (UGPase) encoded by UGPI are not viable. Two strategies were developed to drastically reduce the intracellular concentration of UDP-Glc in order to study the consequences of this metabolic engineering on physiology and morphology. Firstly, UGP1 was placed under the strongly regulatable THI4 promoter. This resulted in a 95% reduction of UGPase activity in the presence of thiamine. The phenotypic effects of this reduction were slightly stronger than those of glucose on the GALI0/CYC1-UGP1 gene fusion [Daran et al. (1995) Eur. J. Biochem. 230, 520-530]. A further reduction of flux towards UDP-Glc was achieved by deletion of the two phosphoglucomutase genes in the ugp1 conditional strain. The growth of this new mutant strain was hardly affected, while it was extremely sensitive to cell wall interfering drugs. Surprisingly, UDP-Glc levels were reduced only by 5-fold, causing a proportional decrease in both glycogen and beta-glucans. Taken altogether, these results indicate that a few percent of enzymatic activities leading to the formation of UDP-Glc appears sufficient to provide the UDP-Glc demands required for cell viability, and that the loss of function of UGP1 is lethal mainly because of the inability of yeast cells to properly form the cell wall.

Phosphorylation of yeast plasma membrane H+-ATPase by casein kinase I

The plasma membrane H+-ATPase of Saccharomyces cerevisiae is subject to phosphorylation by a casein kinase I activity in vitro. We show this casein kinase I activity to result from the combined function of YCK1 and YCK2, two highly similar and plasma membrane-associated casein kinase I homologues. First, H+-ATPase phosphorylation is severely impaired in the plasma membrane of YCK-deficient yeast strains. Furthermore, the wild-type level of the phosphoprotein is restored by the addition of purified mammalian casein kinase I to the mutant membranes. We used the H+-ATPase as well as a synthetic peptide substrate that contains a phosphorylation site for casein kinase I to compare kinase activity in membranes prepared from yeast cells grown in the presence or absence of glucose. The addition of glucose results in increased H+-ATPase activity which is associated with a decline in the phosphorylation level of the enzyme. Mutations in both YCK1 and YCK2 affect this regulation, suggesting that H+-ATPase activity is modulated by glucose via a combination of a "down-regulating" casein kinase I activity and another, yet uncharacterized, "up-regulating" kinase activity. Biochemical mapping of phosphorylated H+-ATPase identifies a major phosphopeptide that contains a consensus phosphorylation site (Ser-507) for casein kinase I. Site-directed mutagenesis of this consensus sequence indicates that Glu-504 is important for glucose-induced decrease in the apparent Km for ATP.

Genetic and biochemical characterization of the UGP1 gene encoding the UDP-glucose pyrophosphorylase from Saccharomyces cerevisiae

We report here that the open reading frame YKL248, previously identified during the systematic sequencing of yeast chromosome XI [Purnelle B., Skala, J., Van Dijck, L. & Goffeau, A. (1992) Yeast 8, 977-986] encodes UDP-glucose pyrophosphorylase (UGPase), the enzyme which catalyses the reversible formation of UDP-Glc from glucose 1-phosphate and UTP. Proof for this function come from sequence alignment of the YKL248 product with UGPase of other species, from complementation studies of an Escherichia coli galU mutant deficient in UGPase activity, and from overexpression studies. In particular, the amino acid sequence motifs involved in the binding of glucose 1-phosphate and UDP-Glc are entirely conserved between the yeast, bovine, human and potato tuber UGPases, and multi-copy expression of YKL248 resulted in a 40-fold increase in UGPase activity. This gene was, therefore, renamed UGP1. Gene disruption at the UGP1 locus in a diploid strain, followed by tetrad analysis, showed that UGPase is essential for cell viability. Functional analysis of UGP1 was, therefore, carried out by generating strains in which UGPase could be either overexpressed or depleted. This was done by generating haploid strains carrying either UGP1 on a multicopy vector or the chromosomal deletion of UGP1, and rescued by a vector bearing the wild-type gene under the control of the glucose-repressible galactose-inducible promoter. The effects of overproducing UGPase on the cell metabolism and morphology were carbon-source dependent. On glucose medium, the 40-fold increase of UGPase activity was restricted to a twofold increase in the concentration of glycogen and UDP-Glc, with no significant effect on growth. In contrast, on galactose, the 40-fold increase in UGPase activity was accompanied by several effects, including a threefold reduction of the growth rate, a 3-5-fold increase in the concentrations of UDP-Glc, UDP-Gal and galactose 1-phosphate, a higher sensitivity to calcofluor white and an increase in the degree of protein glycosylation. Depletion of UGPase activity was performed by transferring the mutant strains from galactose to glucose medium. Unexpectedly, growth of these mutants on glucose was as efficient as that of the control, although the mutants contained only 5-10% wild-type UGPase activity, and a growth defect could never been obtained, even after serial transfers of the mutants to a 10% glucose medium. However, the 10-fold reduction of UGPase activity induced a multi-budding pattern, a higher resistance to zymolyase, a slight increase in the calcofluor sensitivity and a decrease in the cell-wall beta-glucan content. All these alterations, induced by manipulating the UGP1 gene, are discussed in the context of the strategic position of UDP-Glc in yeast metabolism.