Physicochemical properties of hydrogel template-synthesized copper(ii) oxide-modified clay influencing its catalytic activity in toluene combustion

CuO-modified montmorillonite was synthesized by the template-assisted route.

Spectroscopic characterization of Co3O4 catalyst doped with CeO2 and PdO for methane catalytic combustion

The study deals with the XPS, Raman and EDX characterization of a series of structured catalysts composed of cobalt oxides promoted by palladium and cerium oxides. The aim of the work was to relate the information gathered from spectroscopic analyses with the ones from kinetic tests of methane combustion to establish the basic structure-activity relationships for the catalysts studied. The most active catalyst was the cobalt oxide doped with little amount of palladium and wins a confrontation with pure palladium oxide catalyst which is commercially used in converters for methane. The analyses Raman and XPS analyses showed that this catalyst is composed of a cobalt spinel and palladium oxide. The quantitative approach to the composition of the catalysts by XPS and EDX methods revealed that the surface of palladium doped cobalt catalyst is enriched with palladium oxide which provides a great number of active centres for methane combustion indicated by kinetic parameters.

Investigation on the low-temperature transformations of poly(furfuryl alcohol) deposited on MCM-41

MCM-41-type mesoporous silica was used as a support for poly(furfuryl alcohol) deposition. This material was produced by precipitation-polycondensation of furfuryl alcohol (FA) in aqueous slurry of the SiO2 support followed by controlled partial carbonization. By tuning the FA/MCM-41 mass ratio in the reaction mixture, various amounts of polymer particles were introduced on the inner and outer surface of the MCM support. The thermal decomposition of the PFA/MCM-41 composites was studied by thermogravimetry (TG) and spectroscopic techniques (DRIFT, XPS), whereas the evolution of textural parameters with increasing polymer content was investigated using low-temperature adsorption of nitrogen. The mechanism of thermal transformations of PFA deposited on the MCM-41 surface was discussed in detail. It was found that heating at a temperature of about 523 K resulted in opening of the furan rings and the formation of γ-diketone moieties, which were found to be the highest effective surface species for the adsorption of polar volatile organic compounds. A further increase in calcination temperature caused a drop in the amounts of surface carbonyls and the appearance of condensed aromatic domains.

Analysis of deletion phenotypes and GFP fusions of 21 novel Saccharomyces cerevisiae open reading frames

As part of EUROFAN (European Functional Analysis Network), we investigated 21 novel yeast open reading frames (ORFs) by growth and sporulation tests of deletion mutants. Two genes (YNL026w and YNL075w) are essential for mitotic growth and three deletion strains (ynl080c, ynl081c and ynl225c) grew with reduced rates. Two genes (YNL223w and YNL225c) were identified to be required for sporulation. In addition we also performed green fluorescent protein (GFP) tagging for localization studies. GFP labelling indicated the spindle pole body (Ynl225c-GFP) and the nucleus (Ynl075w-GFP) as the sites of action of two proteins. Ynl080c-GFP and Ynl081c-GFP fluorescence was visible in dot-shaped and elongated structures, whereas the Ynl022c-GFP signal was always found as one spot per cell, usually in the vicinity of nuclear DNA. The remaining C-terminal GFP fusions did not produce a clearly identifiable fluorescence signal. For 10 ORFs we constructed 5'-GFP fusions that were expressed from the regulatable GAL1 promoter. In all cases we observed GFP fluorescence upon induction but the localization of the fusion proteins remained difficult to determine. GFP-Ynl020c and GFP-Ynl034w strains grew only poorly on galactose, indicating a toxic effect of the overexpressed fusion proteins. In summary, we obtained a discernible GFP localization pattern in five of 20 strains investigated (25%). A deletion phenotype was observed in seven of 21 (33%) and an overexpression phenotype in two of 10 (20%) cases.

Additional modules for versatile and economical PCR-based gene deletion and modification in Saccharomyces cerevisiae

An important recent advance in the functional analysis of Saccharomyces cerevisiae genes is the development of the one-step PCR-mediated technique for deletion and modification of chromosomal genes. This method allows very rapid gene manipulations without requiring plasmid clones of the gene of interest. We describe here a new set of plasmids that serve as templates for the PCR synthesis of fragments that allow a variety of gene modifications. Using as selectable marker the S. cerevisiae TRP1 gene or modules containing the heterologous Schizosaccharomyces pombe his5+ or Escherichia coli kan(r) gene, these plasmids allow gene deletion, gene overexpression (using the regulatable GAL1 promoter), C- or N-terminal protein tagging [with GFP(S65T), GST, or the 3HA or 13Myc epitope], and partial N- or C-terminal deletions (with or without concomitant protein tagging). Because of the modular nature of the plasmids, they allow efficient and economical use of a small number of PCR primers for a wide variety of gene manipulations. Thus, these plasmids should further facilitate the rapid analysis of gene function in S. cerevisiae.

Heterologous modules for efficient and versatile PCR-based gene targeting in Schizosaccharomyces pombe

We describe a straightforward PCR-based approach to the deletion, tagging, and overexpression of genes in their normal chromosomal locations in the fission yeast Schizosaccharomyces pombe. Using this approach and the S. pombe ura4+ gene as a marker, nine genes were deleted with efficiencies of homologous integration ranging from 6 to 63%. We also constructed a series of plasmids containing the kanMX6 module, which allows selection of G418-resistant cells and thus provides a new heterologous marker for use in S. pombe. The modular nature of these constructs allows a small number of PCR primers to be used for a wide variety of gene manipulations, including deletion, overexpression (using the regulatable nmt1 promoter), C- or N-terminal protein tagging (with HA, Myc, GST, or GFP), and partial C- or N-terminal deletions with or without tagging. Nine genes were manipulated using these kanMX6 constructs as templates for PCR. The PCR primers included 60 to 80 bp of flanking sequences homologous to target sequences in the genome. Transformants were screened for homologous integration by PCR. In most cases, the efficiency of homologous integration was > or = 50%, and the lowest efficiency encountered was 17%. The methodology and constructs described here should greatly facilitate analysis of gene function in S. pombe.

Saccharomyces cerevisiae cells with defective spindle pole body outer plaques accomplish nuclear migration via half-bridge-organized microtubules

Cnm67p, a novel yeast protein, localizes to the microtubule organizing center, the spindle pole body (SPB). Deletion of CNM67 (YNL225c) frequently results in spindle misorientation and impaired nuclear migration, leading to the generation of bi- and multinucleated cells (40%). Electron microscopy indicated that CNM67 is required for proper formation of the SPB outer plaque, a structure that nucleates cytoplasmic (astral) microtubules. Interestingly, cytoplasmic microtubules that are essential for spindle orientation and nuclear migration are still present in cnm67Delta1 cells that lack a detectable outer plaque. These microtubules are attached to the SPB half- bridge throughout the cell cycle. This interaction presumably allows for low-efficiency nuclear migration and thus provides a rescue mechanism in the absence of a functional outer plaque. Although CNM67 is not strictly required for mitosis, it is essential for sporulation. Time-lapse microscopy of cnm67Delta1 cells with green fluorescent protein (GFP)-labeled nuclei indicated that CNM67 is dispensable for nuclear migration (congression) and nuclear fusion during conjugation. This is in agreement with previous data, indicating that cytoplasmic microtubules are organized by the half-bridge during mating.

Heterologous HIS3 marker and GFP reporter modules for PCR-targeting in Saccharomyces cerevisiae

We have fused the open reading frames of his3-complementing genes from Saccharomyces kluyveri and Schizosac-charomyces pombe to the strong TEF gene promotor of the filamentous fungus Ashbya gossypii. Both chimeric modules and the cognate S. kluyveri HIS3 gene were tested in transformations of his3 S. cerevisiae strains using PCR fragments flanked by 40 bp target guide sequences. The 1.4 kb chimeric Sz. pombe module (HIS3MX6) performed best. With less than 5% incorrectly targeted transformants, it functions as reliably as the widely used geniticin resistance marker kanMX. The rare false-positive His+ transformants seem to be due to non-homologous recombination rather than to gene conversion of the mutated endogenous his3 allele. We also cloned the green fluorescent protein gene from Aequorea victoria into our pFA-plasmids with HIS3MX6 and kanMX markers. The 0.9 kb GFP reporters consist of wild-type GFP or GFP-S65T coding sequences, lacking the ATG, fused to the S. cerevisiae ADH1 terminator. PCR-synthesized 2.4 kb-long double modules flanked by 40-45 bp-long guide sequences were successfully targeted to the carboxy-terminus of a number of S. cerevisiae genes. We could estimate that only about 10% of the transformants carried inactivating mutations in the GFP reporter.

The nucleotide sequence of Saccharomyces cerevisiae chromosome XIV and its evolutionary implications

In 1992 we started assembling an ordered library of cosmid clones from chromosome XIV of the yeast Saccharomyces cerevisiae. At that time, only 49 genes were known to be located on this chromosome and we estimated that 80% to 90% of its genes were yet to be discovered. In 1993, a team of 20 European laboratories began the systematic sequence analysis of chromosome XIV. The completed and intensively checked final sequence of 784,328 base pairs was released in April, 1996. Substantial parts had been published before or had previously been made available on request. The sequence contained 419 known or presumptive protein-coding genes, including two pseudogenes and three retrotransposons, 14 tRNA genes, and three small nuclear RNA genes. For 116 (30%) protein-coding sequences, one or more structural homologues were identified elsewhere in the yeast genome. Half of them belong to duplicated groups of 6-14 loosely linked genes, in most cases with conserved gene order and orientation (relaxed interchromosomal synteny). We have considered the possible evolutionary origins of this unexpected feature of yeast genome organization.

Identification of a gene encoding a homocitrate synthase isoenzyme of Saccharomyces cerevisiae

In Saccharomyces cerevisiae, most of the LYS structural genes have been identified except the genes encoding homocitrate synthase and alpha-aminoadipate aminotransferase. Expression of several LYS genes responds to an induction mechanism mediated by the product of LYS14 and an intermediate of the pathway, alpha-aminoadipate semialdehyde (alpha AASA) as an inducer. This activation is modulated by the presence of lysine in the growth medium leading to an apparent repression. Since the first enzyme of the pathway, homocitrate synthase, is feedback inhibited by lysine, it could be a major element in the control of alpha AASA supply. During the sequencing of chromosome IV of S. cerevisiae, the sequence of ORF D1298 showing a significant similarity with the nifV gene of Azotobacter vinelandii was reported. Disruption and overexpression of ORF D1298 demonstrate that this gene, named LYS20, encodes a homocitrate synthase. The disrupted segregants are able to grow on minimal medium and exhibit reduced but significant homocitrate synthase indicating that this activity is catalysed by at least two isoenzymes. We have also shown that the product of LYS20 is responsible for the greater part of the lysine production. The different isoforms are sensitive to inhibition by lysine but only the expression of LYS20 is strongly repressed by lysine. The N-terminal end of homocitrate synthase isoform coded by LYS20 contains no typical mitochondrial targeting sequence, suggesting that this enzyme is not located in the mitochondria.

Stepwise assembly of the lipid-linked oligosaccharide in the endoplasmic reticulum of Saccharomyces cerevisiae: identification of the ALG9 gene encoding a putative mannosyl transferase

The core oligosaccharide Glc3Man9GlcNAc2 is assembled at the membrane of the endoplasmic reticulum on the lipid carrier dolichyl pyrophosphate and transferred to selected asparagine residues of nascent polypeptide chains. This transfer is catalyzed by the oligosaccharyl transferase complex. Based on the synthetic phenotype of the oligosaccharyl transferase mutation wbp1 in combination with a deficiency in the assembly pathway of the oligosaccharide in Saccharomyces cerevisiae, we have identified the novel ALG9 gene. We conclude that this locus encodes a putative mannosyl transferase because deletion of the gene led to accumulation of lipid-linked Man6GlcNAc2 in vivo and to hypoglycosylation of secreted proteins. Using an approach combining genetic and biochemical techniques, we show that the assembly of the lipid-linked core oligosaccharide in the lumen of the endoplasmic reticulum occurs in a stepwise fashion.

PCR-synthesis of marker cassettes with long flanking homology regions for gene disruptions in S. cerevisiae

A PCR-method for fast production of disruption cassettes is introduced, that allows the addition of long flanking homology regions of several hundred base pairs (LFH-PCR) to a marker module. Such a disruption cassette was made by linking two PCR fragments produced from genomic DNA to kanMX6, a modification of dominant resistance marker making S. cerevisiae resistant to geneticin (G418). In a first step, two several hundred base pairs long DNA fragments from the 5'- and 3'- region of a S. cerevisiae gene were amplified in such a way that 26 base pairs extensions homologous to the kanMX6 marker were added to one of their end. In a second step, one strand of each of these molecules then served as a long primer in a PCR using kanMX6 as template. When such a LFH-PCR-generated disruption cassette was used instead of a PCR-made disruption cassette flanked by short homology regions, transformation efficiencies were increased by at least a factor of thirty. This modification will therefore also help to apply PCR-mediated gene manipulations to strains with decreased transformability and/or unpredictable sequence deviations.