bluuebunny/crossref_metadata_2025 huggingface dataset:
SEM, EDX and XRD studies of the scales formed on the Fe–Mn–Al–C system in oxidizing–sulphidizing environments
Authors: Tjong S. C.
Published: May 2005

The use of Fe–Mn–Al–C alloys in oxidizing–sulphidizing environments at elevated temperatures is considered. Applications of SEM, EDX mapping and x‐ray diffraction techniques to the microstructural characterization of the scale development on these alloys are reviewed. Combination of the electron microscope and the analytical techniques provides information concerning the morphology, elemental distribution, crystal structure and identification of phases in the scale. This information is of particular importance in the design and development of a corrosion‐resistant alloy. Application of the above techniques is described with examples from oxidation studies in air and corrosion studies in SO2–O2 gas mixtures with different sulphur partial pressures.
Current trends in the literature on x‐ray emission spectrometry
Authors: Van Grieken R. , Markowicz A. , Veny P.
Published: May 2005

Based on a computerized literature search through Chemical Abstracts for the period 1968–89 and on a manual search through Analytical Abstracts for 1988, trends in the literature are discussed for x‐ray emission spectrometry in general, and for x‐ray fluorescence analysis, proton‐induced x‐ray emission and synchrotron‐induced x‐ray fluorescence analysis. Relative contributions are derived for articles dealing with various excitation and detection modes, with different application fields and from different countries. Special attention is paid toenvironmental applications of x‐ray emission spectrometry.
Matrix correction in x‐ray fluorescence analysis by the effective coefficient method
Authors: Broll Norbert , Caussin Pierre , Peter Markus
Published: May 2005

Up till now, the well known effective coefficient method was used by referring to a single standard. The SFP (Siemens fundamental parameter) program additionally allows this method to be employed with several standards and to analyse samples containing an element that is not analysed. A modified algorithm, called the trace model, yields an improvement in the precision of the trace element analysis. The different variants are illustrated by practical applications.
Carbon Kα peak shift study using an electron probe microanalyzer with a vanadium–carbon multilayer pseudo‐crystal
Authors: Liang Long C.
Published: May 2005

A study of carbon Kα peak shifts using an electron probe micronalyzer (EPMA) with a vanadium‐carbon multilayer pseudo‐crystal (2d = 96 Å) shows a distinct peak shift between diamond and graphite and two organic carbon phases (asphaltene and vitrinite). The peak shift reflecting the difference in carbon‐to‐carbon bonding types and structures shows that the carbon electron binding energy of diamond is higher than that of graphite, asphaltene and vitrinite. The relative electron binding energies of these phases obtained from the EPMA study were confirmed by ESCA (electron spectroscopy for chemical analysis) data.
Accurate description of surface ionization in electron probe microanalysis: An improved formulation
Authors: Merlet Claude
Published: May 2005

A new analytical expression of the surface ionization Φ(0) is derived in terms of atomic number and overvoltage. This expression is obtained by means of an analytical description of the energy distribution of backscattered electrons. The Φ(0) data for Pt, W, Sb, InSb, Ni, Co and Mg have been measured using the tracer technique. The Φ(0) values obtained by using the new expression compare more favourably with experimental results, Monte Carlo simulation and backscattering data from the literature than those obtained with the previous analytical models.
High‐order multiple scattering contributions in x‐ray spectrometry
Authors: Sartori R. , Fernández J. E.
Published: May 2005

Multiple scattering contributes important parts to the emission spectrum from thick targets excited with x‐ray photons. Both the continuous and discrete parts of the spectrum receive enhancement by multiple scattering. Recently, some expressions were deduced in the framework of transport theory allowing the computation of the second‐order chains of the Compton and Rayleigh effects. In this work those calculations were extended to the third and the fourth orders of multiple scattering by means of Monte Carlo simulation. Monte Carlo results were computed using full expressions for the angular kernels (i.e. scattering coefficients including atomic form factors). The second‐order Monte Carlo result was compared with the computation by deterministic means, showing close agreement except in the extreme of the Compton‐Compton spectrum. Higher orders are important for low‐Z elements but can be safely neglected in the medium‐Z range.
Simulation of relationships between substrate XRF intensities and film thicknesses
Authors: Fan Qinmin
Published: May 2005

A Monte Carlo method was used to simulate relationships between substrate XRF intensities and film thicknesses for nickel film– and tin film–substrate systems. Experimental measurements of these relationships were performed for a few film–substrate systems. Good agreement between simulated and experimental values was obtained.
Characterization of environmental dusts by x‐ray fluorescence spectrometry using a micro bead presentation
Authors: Moore Lynne V.
Published: May 2005

Small dust samples of mass ca. 0.07 g are fused with a lithium fluoride–lithium tetraborate flux to yield a homogeneous micro bead. These beads are presented to a wavelength‐dispersive spectrometer and the composition of the sample derived from calibrations effected with international standards. Matrix corrections are calculated by an NBSGSC algorithm.
Monte Carlo simulation of conventional and synchrotron energy‐dispersive x‐ray spectrometers
Authors: Janssens K. , Vincze L. , Van Espen P. , Adams F.
Published: May 2005

A number of examples of the use of a detailed Monte Carlo (MC) simulation program for EDXRF spectrometers is discussed. The MC code is employed to predict the complete spectral response of a polychromatic EDXRF spectrometer using different excitation conditions. With respect to quantification of steel samples in which significant enhancement and self‐absorption occur, the usefulness of the code in simulating spectra corresponding to calibration standards is demonstrated. An extension of the program that deals with simulating the interaction of polarized radiation with matter is used to estimate the analytical qualities of currently operating and future mono‐and polychromatic synchrotron radiation XRF spectrometers.
Multi‐element analysis of tree rings by EDXRF spectrometry
Authors: Selin E. , Standzenieks P. , Boman J. , Teeyasoontranont V.
Published: May 2005

An EDXRF system for scanning samples in steps of 5 μm was developed. The system is based on a conventional x‐ray tube and secondary target in closest possible geometry. For tree ring analysis, which was made in steps of 200 μm, the exciting x‐ray beam was allowed to pass through a slit collimator of dimensions 0.1 × 1 mm made of pure silver. The sample holder is movable in steps of 5 μm in three orthogonal directions. The beam path of the exciting and fluorescent radiation can be adjusted in relation to the sample plane by the movable sample holder. Further adjustments can be made by a movable detector platform. All movements are driven by microcomputercontrolled step motors. The detection limits of thick samples, like tree biopsies, are of the order of parts per million for medium‐heavy elements. The system was applied to multielement analysis of healthy samples of pine, birch and spruce biopsies. Long‐term trends in some trace element concentrations could be seen in these samples, together with the possible influence of stress.
EDXRS modelling for in vivo trace element analysis by using the SHAPE code
Authors: Tartari A. , Fernandez J. E. , Casnati E. , Baraldi C. , Felsteiner J.
Published: May 2005

The validity of the SHAPE code, a computer package able to simulate EDXRS spectra, was tested to model the in vivo XRF determination of cadmium concentrations in the kidney by choosing the best source–measurement geometry combination. Accurate measurements were performed in order to validate the results of this code in the energy interval involved in in vivo XRF analysis. In addition, a comparison was made with Monte Carlo results including thrid‐order contributions and polarization. Very good agreement was found with the experimental and Monte Carlo results. In spite of the fact that, at present, this code does not include higher order multiple scattering, modelling results using the SHAPE code agree very well with the expensive Monte Carlo solutions and the empirical values recently predicted for this technique.
Determination of potassium and calcium in vegetables by x‐ray fluorescence spectrometry
Authors: Mittal Raj , Allawadhi K. L. , Sood B. S. , Singh N. , Kumar Anita , Kumar Parminder
Published: May 2005

A method based on XRF was used for the determination of the total concentration of potassium and calcium, in the presence of each other and irrespective of the nature of their chemical compounds, in the roots and leaves of spinach and radish plants. The enhancement of potassium K x‐rays due to K x‐rays of calcium present in the samples was avoided by selective excitation of the sample with external conversion calcium K x‐rays in a compact triaxial double reflection geometry set‐up. The absorption of calcium and potassium K x‐rays in the samples was taken care of in terms of counts under K x‐ray peaks only. The overlapping of the calcium K x‐ray photopeak with the potassium K x‐ray photopeak due to the limited resolution of the Si(Li) spectrometer was estimated and counts under the calcium K x‐ray photopeak were corrected accordingly. The results for whole plants of spinach and radish agreed with those normally quoted in nutrition books.
Bent and flat highly oriented pyrolytic graphite crystals as small bragg angle monochromators in thin‐specimen energy‐dispersive XRF analysis
Authors: Beckhoff Burkhard , Laursen Jens
Published: May 2005

A monochromatic high‐intensity x‐ray beam, obtained by Bragg reflection of the strongest characteristic tube line under small angles on single crystals, can be used as an EDXRF excitation source. A systematic selection procedure and search of 55 single crystals suitable as EDXRF Bragg reflectors was made and highly oriented pyrolytic graphite (HOPG) was found to be a superior candidate for the characteristic Kα line of an Mo tube within the range of low‐order reflections, yielding the highest intensities. Meridionally and sagitally curved HOPGs were studied in a flexible experimental set‐up and the reflected beam intensity and profile were compared with the corresponding data obtained from flat HOPGs with different mosaic spreads. The relationships between collimation, crystal curvature and mosaic spread were evaluated. The experimental angular beam acceptance and the secondary extinction effects dependent on the mosaic spread of the HOPG were found to be in line with theoretical expectations. Measured in similar configurations as required for realistic EDXRF applications, the sagitally bent HOPG increases the reflected beam intensity up to 77% whereas the meridionally bent HOPG yields an intensity gain of only up to 28% compared with the flat crystal with the same mosaic spread. The detection limits for the corresponding thin‐filter EDXRF analysis are presented.
Monte carlo simulation of the scattering contributions to the XRF line
Authors: JorgeSánchez Héctor , Sartori Renzo
Published: May 2005

A Monte Carlo program to simulate the scattering contributions to the x‐ray fluorescent line was developed. Simulations were carried out on three pure samples (Z = 14, 28 and 40) in several geometrical situations (incident and take‐off directions of the photons). The results show that the scattering effects do not exceed 4% for the analysed elements in the X‐ray regime. Good agreement between normal incidence simulations and theoretical results was found. The vanishing of second‐order interactions inside the sample when the propagation plane approximates π/2 was also verified.
Determination of fractal dimension in cement gels by PIXE
Authors: Potiriadis C. , Bakopoulos Y.
Published: May 2005

Two samples of ordinary Portland cement, one consisting of dry powder and the other of hydrated paste 28 days old, were bombarded with protons, resulting in proton‐induced X‐ray emission (PIXE). The X‐ray yield was measured as a function of the exit angle and the differences between the two samples were interpreted by the hypothesis that the pores of the hydrated cement gel form a fractal. The fractal dimension that was calculated is in good agreement with the values found by small‐angle neutron scattering and nuclear magnetic resonance.
Determination of the mean size of submicron particles by electron probe microanalysis
Authors: Berner A. , Levin I. , Klinger L. , Brandon D. G.
Published: May 2005

A method for the determination of the mean size of submicron particles randomly distributed in a matrix by electron probe x‐ray microanalysis (EPMA) is described. The method is based on an analysis of variance of the characteristic x‐ray intensity from an element contained only in the particle. Analytical expressions relating this variance to the mean size of the particles were derived and the method was validated using test samples. The present technique can be used with a conventional x‐ray microanalyser for the rapid determination of the mean size of submicron particles.
Detailed ray‐tracing code for capillary optics
Authors: Vincze L. , Janssens K. , Adams F. , Rindby A.
Published: May 2005

A description of a detailed ray‐tracing code for capillary optics is given and a number of examples of the use of the program are discussed. The model uses numerically defined capillary shapes and is able to simulate the behaviour of devices having shape distortions of various nature, including bending of the capillary. Comparisons are made with previously published capillary calculation models and with experimental results described in the literature. The use of the code is also demonstrated for the optimization of conical capillary dimensions assuming extended x‐ray sources. With respect to the modelling of realistic capillary shapes, the beam transmission properties of an ellipsoidal device are calculated, using the experimentally determined capillary profile.
Determination of thickness maps of thin coatings by EDS EPMA
Authors: Benhayoune H. , Jbara O. , Thomas X. , Cazaux J.
Published: May 2005

A new experimental procedure for the measurement of the thickness fo thin coatings on substrates is presented. Based on the experimental determination of the electron backscattering coefficient η (via the measurement of the electric current of the correctly polarized specimen holder), the number of reference specimens to be used for the calibration during measurements can be reduced. Thickness maps free of artifacts associated with local changes in the substrate composition illustrate the proposed methods.
EDXRF procedure for quantitative analysis matching theoretically generated reference spectra to measured spectra
Authors: Fernández J. E. , Tartari A.
Published: May 2005

The diversity of processes that contribute to an x‐ray fluorescence spectrum make it difficult to obtain an accurate estimate of the line intensities needed to determine the sample composition in XRF analysis. The radiative contributions forming the spectrum are produced by the interactions that x‐ray photons undergo with the atoms of the sample. Many multiple scattering terms contribute to the continuous portions of spectrum that overlap the lines of interest. The lines themselves are formed by the overlap of many narrow (discrete) contributions and some continuous ones: one ‘primary intensity’ plus several enhancement terms. The lines can also interfere with other neighbouring lines produced in the sample. The resulting spectrum, sufficiently complicated at this stage, is still modified in a complex way by the influence of the detector response and successive digitalization by the multi‐channel analyser. The difficulties that such spectral complexity introduces in the process of extracting the ‘primary fluorescence intensity’ from the experimental spectrum can be overcome by using a theoretical spectrum of reference that, in this paper, was calculated using the code SHAPE. Such a theoretical spectrum has the property that all the single contributions are well known, and therefore can be used to estimate correctly the fraction of ‘primary fluorescence intensity’ under any experimental line of interest in the real spectrum enclosed between two given energy channels. Since the theoretical spectrum can be computed only for a known composition, the calculated fraction can be initially obtained by feeding SHAPE with an arbitrary composition. The fraction estimated with the theoretical spectrum is used to correct the corresponding peak area in the experimental measured spectrum, which in turn is used to obtain a new calculated composition. This result is used to feed a new spectrum computation, defining an iterative method that converges to the unknown composition. The theoretical details of this iterative method are described and some experimental examples of EDXRF analysis using this technique are given. The advantages of the method for treating some paradigmatic cases of analysis are also illustrated.
Partial restoration of meiosis in an apomictic strain of Saccharomyces cerevisiae: A model system for investigation of nucleomitochondrial interactions during sporulation
Authors: Marmiroli Nelson , Bilinski Carl A.
Published: May 2005

In an apomitic strain of Saccharomyces cerevisiae (ATCC 4117‐H2) which undergoes a single nuclear division during sporulation and consequently forms asci containing two uninucleate diploid spores, a study was undertaken to investigate the effects of cultivation in three presporulation media (YPA; YNB; SMM) on nuclear division and ascoporogenesis in sporulation medium. Comparison of effects of presporulation culture in these media on the number of spores formed per ascus showed that a marked induction (30 ± 4·3 per cent) of three‐ and four‐spored asci could occur in sporulation medium following cultivation in a defined YNB medium supplemented with a 1 per cent solution of vitamins and containing decreased ammonium sulphate and increased glucose levels. Experiments in which the concentrations of glucose and of ammonium sulphate were varied simultaneously indicated that the initial presporulation carbon to nitrogen source ratio is an important factor in determining tetrad formation in sporulation medium. Nuclear staining demonstrated two classes of asci: binucleate (one‐ and two‐spored) and tetranucleate (three‐ and four‐spored). Genetic evidence and data concerning effects of inclusion in sporulation medium of a meiotic inhibitor (glucose) indicated spores in tetrads were haploid rather than diploid. This ability to condition a significant number of cells for meiotic rather than apomictic differentiation made possible investigation of effects of mitochondrial inhibitors on both developmental processes simultaneously. It was found possible to selectively inhibit meiotic development by inclusion in sporulation medium of appropriate concentrations of specific inhibitors. Moreover, the data suggest meiotic sporulation is more strictly dependent than apomictic sporulation on mitochondrial function.
Yeast/E. coli shuttle vectors with multiple unique restriction sites
Authors: Hill John E. , Myers Alan M. , Koerner T. J. , Tzagoloff Alexander
Published: May 2005

Two yeast/E. coli shuttle vectors have been constructed. The two vectors, YEp351 and YEp352, have the following properties: (1) they can replicate autonomuosly in Saccharomyces cerevisiae and in E. coli; (2) they contain the β‐lactamase gene and confer ampicillin resistance to E. coli; (3) they contain the entire sequence of pUC18; (4) all ten restriction sites of the multiple cloning region of pUC18 including EcoRI, SacI, KpnI, SmaI, BamH1, XbaI, SbaI, SalI, PstI, SphI and HindIII are unique in YEp352; these sites are also unique in YEp351 except for EcoRI and KpnI, which occur twice; (5) recombinant plasmids with DNA inserts in the multiple cloning region of YEp351 and YEp352 can be recognised by loss of β‐galactosidase function in appropriate E. coli hosts; (6) YEp351 and YEp352 contain the yeast LEU2 and URA3 genes, respectively, allowing for selection of these grown under non‐selective conditions indicative of high plasmid copy number. The above properties make the shuttle vectors suitable for constructions of yeast genomic libraries and for cloning of DNA fragments defined by a large number of different restriction sites.

The two vectors have been further modified by deletion of the sequences necessary for antunomous replication in yeast. The derivative plasmids YIp651 and YIp352 can therefore be used ti integrate specific sequences into yeast chromosomal DNA.
Cell division age dependency of meiosis in an apomictic variant of Saccharomyces cerevisiae
Authors: Bilinski Carl A. , Marmiroli Nelson , Miller John J.
Published: May 2005

The cell division age dependency of sporulation was investigated in a diploid strain of Saccharomyces cerevisiae (19el) which undergoes a single equational nuclear division during sporulation with consequent formation of asci containing two uninucleate diploid spores (apomictic dyads). Under modified nutritional conditions which partially restore meiosis and hence normal tetrad formation, newly formed (age 0) daughter cells were observed to be capable of formation of apomictic dyads but not of meiotic tetrads. Even under conditions in which only apomictic dyads developed, approximately 20% of the asci resulted from differentiation of newborn ‘inexperienced’ cells. Thus, the data indicated production of at least one bud to be a prerequisite for meiosis but not for apomixis; however, occurrence of at least one complete mitotic cell division cycle was evidently insufficient for the morphogenetic switch from diploid to haploid spore formation, since older cells bearing several bud scars often underwent apomictic dyad development, and some produced no spores.
Sterility (ste) genes of Schizosaccharomyces pombe
Authors: Michael Holger , Gutz Herbert
Published: May 2005

In previous experiments of Girgsdies (1982), eight sterile (ste) mutants of Schizosaccharomyces pombe did not sporulate when fused with h+ or h− protoplasts. We succeeded in achieving sporulation with these mutants. Two hitherto unknown ste genes, ste7 and ste8, were found.
Biochemical estimation of hepatitis B surface antigen in recombinant yeast
Authors: Wingfield Paul T. , Graber Pierre , Payton Mark A.
Published: May 2005

Purified recombinant hepatitis B surface antigen separated on polyacrylamide gels in the presence of sodium dodecyl sulphate has a very low staining index with Coomassie blue relative to a number of standard proteins. In contrast the protein stains better than average with silver nitrate. This property has been used to develop a semi‐quantitative method of estimation of recombinant surface antigen in extracts of Saccharomyces cerevisiae producing this protein. The method can be used to follow purification protocols. It is quick, simple and since it measures the surface antigen biochemically, is independent of the aggregation state or conformation of the protein, a factor which can affect enzyme‐linked immunoassays which rely on antigen–antibody interactions.
Artifactual immunofluorescent labelling in yeast, demonstrated by affinity purification of antibody
Authors: Lillie S. H. , Brown S. S.
Published: May 2005

In the course of making antibodies against various yeast (S. cerevisiae) proteins, we have noted that it is common to observe reactivity of rabbit sera with a number of extraneous bands on Western transfers of yeast proteins. The pattern of reactive bands can change within a period of weeks, even when the rabbit has not been injected with antigen. A simple method of affinity purification, using antigen bound to nitrocellulose, is employed to remove the reactivity with these extraneous bands from immune sera. The importance of affinity purification is demonstrated by our attempts to immunolocalize a 55 kd yeast protein (p55). Immune serum stains yeast cells to give a striking pattern of spots and blotches not seen with preimmune serum. However, affinity purification of anti‐p55 antibody shows that this pattern is not due to staining by anti‐p55 antibody; rather the pattern is due to staining left in the serum depleted of anti‐p55 antibody.
Specificity of DNA uptake during whole cell transformation of S. cerevisiae
Authors: Bruschi Carlo V. , Comer Allen R. , Howe Gregg A.
Published: May 2005

We have studied the mechanism of DNA transformation of whole yeast cells in Saccharomyces cerevisiae with particular emphasis on the role of the cell wall complex in DNA uptake. Two new aspects of the process have been investigated in order to evaluated its specificity. Such aspects are: (i) effect of monovalent vs. divalent cations during incubation with the transforming DNA and (ii) timing of DNA adsorption and uptake. We found that the specificity for cation requirement is a strain‐dependent characteristic influenced by the presence of transforming DNA in the cell suspension. This finding is supported by reports from several laboratories that some yeast strains show mutually exclusive transformability with monovalent vs. divalent cations. While irreversible adsorption of plasmid DNA molecules is induced by both heat shock and polyethylene‐glycol(PEG), DNA uptake seems to occur only after the removal of PEG. In the course of this study we have developed a new, alternative method of whole cell DNA transformation with CaCl2 able to transform strains that do not respond to other methods.
Expression of two Trichoderma reesei endoglucanases in the yeast Saccharomyces cerevisiae
Authors: Panttilä Merja E. , André Lars , Saloheimo Markku , Lehtovaara Päivi , Knowles Jonathan K. C.
Published: May 2005

The cDNA copies of the two endo‐β‐1,4‐glucanase genes, egl1 and egl3, from the filamentous fungus Trichoderma reesei were expressed in yeast Saccharomyces cerevisiae under the control of the yeast phosphoglycerate kinase gene promoter. Active EGI and EGIII enzyme was produced and secreted by yeast into the growth medium. The recombinant EGI enzyme was larger and more heterogeneous in size than the native enzyme secreted by Trichoderma, due to differences in the extent of N‐glycosylation between these two organisms. The morphology of the yeast cells producing EGI or EGIII was clearly different from control strain.
Purification of isocitrate lyase from Saccharomyces cerevisiae
Authors: Lopez‐Boado Yolanda S. , Herrero Pilar , Fernandez Maria‐Teresa , Fernandez Rose , Moreno Fernando
Published: May 2005

Isocitrate lyase purified to homogeneity from Saccharomyces cerevisiae was composed of four identical subunits with a molecular mass 75 K Da. The enzyme was most active at pH 7.0 in the presence of 5 mM‐Mg2+. The Km value for threo‐Ds‐isocitrate was 1.4 mM. Isocitrate lyase was shown to be thermostable at 50°C for 60 min at a high salt concentration, but rapidly lost activity at −20°C or by dialysis.
Physiological and biochemical analysis of cytochrome P‐450 in the yeast Schizosaccharomyces pombe
Authors: Bligh H. F. J. , Kelly S. L.
Published: May 2005

The yeast Schizosacchromyces pombe has been shown to contain a microsomal cytochrome P‐450 (cyt. P‐450) inducible under conditions of glucose repression. Under these conditions the enzyme has maximal expression of 0.43 nmol g−1 wet wt at the end of the exponential phase of growth. Substrate and inhibitor affinity was examined using studies of spectral changes on binding and revealed a type II spectrum with ketoconazole (Ks = 23 μM) and a type I spectrum with benzo(a)pyrene (Ks = 77 μM). A Km of 112 μM was found in the aryl hydrocarbon hydroxylas assay. These properties show broad comparability with the cyt. P‐450 of Saccharomyces cerevisiae.
Metabolism of 2,3‐butanediol in yeasts
Authors: Verduyn Cornelis , Breedveld Guido J. , Scheffers W. Alexander , Van Dijken Hohannes P.
Published: May 2005

The biochemistry and physiology of 2,3‐butanediol metabolism has been studied in a number of selected yeast species. Candida utilis CBS 621 exhibited diauxic growth on 2,3‐butanediol. The first phase was characterized bu the utilization of the two optically active stereoisomers and associated accumulatoin. In the second phase of growth the meso‐form of 2,3‐butanediol was utilized together with acetoin. An attempt is made to explain these phenomena on the basis of the substrate specificity of the two enzymes which oxidize 2,3‐butanediol in C. utilis. Although whole cells oxidized acetoin and diacetyl at high rates, attempts to identify the enzymes responsible for these oxidations were unsuccessful. In C. utilis and other yeasts metabolism of 2,3‐butanediol probably involves a cleavage of the substrate into C2‐units which are assimilated by the glyoxylate cycle. In the few yeasts which have been found to grow on 2,3‐butanediol differences may be encountered with respect to the substrate specificity for the three stereoisomers of 2,3‐butanediol. For example, Candida salmanticensis CBS 5121 showed no diauxis growth and utilized only two of three stereomers.
Polyploid fragile strains of Saccharomyces cerevisiae—a novel source of proteins for nutritional purposes
Authors: Stateva L. I. , Venkov P. V. , Hadjiolov A. A. , Koleva L. A. , Lyudskahov N. L.
Published: May 2005

A series of prototrophic fragile strains of different ploidy (2n, 3n and 4n) has been genetically constructed on the basis ofhalopoid srb1 containing segregants of the fragile Saccharomyces cerevisiae mutant VY 1160. The strains have been characterized by several criteria. In regard to generation time, biomass yield, and nucleic acids content of the cells, the tetraploid srb1 homozygous hybrid is indistinguishable from an industrial strain of S. cerevisiae. However, it is characterized by a higher protein content. Unlikely any other laboratory or industrial strains, the original mutant and these hybrids possess an ability for lysis upon suspension in hypotonic solutions. The dependence of the percentge of lysed cells on the growth phase and concentration of osmotic stabilizer in the medium has been investigated. The quantity of proteins in the soluble fractions obtained after lysis of these strains by osmotic shock has been determined. These hybrids can be considered as a potential industrial source of potentials for nutritional purposes.
Membrane transport in an osmotically fragile mutant of Saccharomyces cerevisiae
Authors: Kotyk A. , Venkov P. , Dvor̆áková M.
Published: May 2005

Transport properties of the osomotically fragile strain VY1160 of saccharomyces cerevisiae were compared with those of the parent S288c strain. Mediated diffusion of 6‐deoxy‐D‐glucose was practically unaffected; membrane‐potential dependent transport of D‐glucosamine was very much depressed in the fragile strain. The H+ ‐driven transport of L‐lysine and Lproline, as well as that of the hitherto uninvestigated D‐glucose‐6‐phosphate, were also very depressed. 2‐Deoxy‐D‐glucose transport displayed slightly different kinetic parameters. Primary H+ extrusion by the plasma membrane H‐ATPase was not diminished althpough the ATP‐splitting activity was depressed by about 50%. The overall proton‐motive force (pmf) of the fragile mutant at pH 5.5 was only m V while in the parent strain it was 108 m V. In parallel with this, spontaneous acidfication of the external medium to stimulate (a CO2‐associated event) was only about 2% of that in the parent strain. The defect in his, together with the inability to stimulate transport protein synthesis by glucose, may account for the generally poorer transport performance of the fragile mutant.
Cloning and characterization of Baker's yeast α‐glucosidase: Over‐expression in a yeast strain devoid of vacuolar proteinases
Authors: Kopetzki Erhard , Buckel Peter , Schumacher Guenter
Published: May 2005

Two α‐glucosidase (maltase) genes, designated GLUCPI and GLUCPII, have been cloned from an industrial strain of baker's yeast (Saccharomyces cerevisiae) by complementation of a maltase‐negative mutant strain. The different genes were identified according to their alternatively expressed isoenzymes PI and PII in transformants after isoelectric focusing and activity staining in separated cell lysates. The gene encoding α‐glucosidase PI (GLUCPI), which was not present in laboratory strains of S. carlsbergensis with a defined MAL1, 2, 3, 4 or 6 locus, was sequenced and compared with the recently published MAL6S gene. This comparison revealed single amino acid deviations at three positions in the predicted polypeptide sequence. In addition, the divergent promoter region of GLUCPI differed from MAL6S by a triple repeated 147‐bp DNA segment. Maltose induction and glucose repression of α‐glucosidase PI were not affected by the deletion of the repeated DNA segment. However, the absolute expression of α‐glucosidase PI increased two‐ to four‐fold. In addition, a two‐fold increase in the maltase synthesis occurred when the cloned positive regulator gene MAL2‐8cp was on the same plasmid. Furthermore, stability of the α‐glucosidase in cultures in the stationary growth phase was greatly enhanced using a host strain lacking the proteinases A and B and the carboxypeptidases Y and S. Promoter trimming, MAL2‐8cp stimulation and the use of a host strain deficient in four vacuolar proteinases resulted in α‐glucosidase PI expression of about 13% of the soluble protein.
Vanadate inhibition of mitochondrial respiration and H+ ATPase activity in Saccharomyces cerevisiae
Authors: Henderson Gillian E. , Evans Ivor H. , Bruce Ian J.
Published: May 2005

The effects of vandate on mitochondrial respiration and H+ ATPase activity in Saccharomyces cerevisiae were studied. A 50% inhibition of oxygen uptake in isolated mitochondria was produced by 4·4 mM‐V2O5. Activity of H+ ATPase in whole mitochondria was inhibited by 50% by 5·5 μM‐V2O5, in submitochondrial particles by 55 μM‐V2O5; and in the chloroform‐released H+ ATPase by 0·5 mM‐V2O5. Vandate was also found to relieve growth inhibition caused by the mitochondrial H+ ATPase inhibitors NN′‐decyclohexylcarbodiimide and oligomycin. These results imply that vanadate could affect mitochondrial respiration by interacting with the H+ ATPase in S. cerevisiae.
Mutants of the methylotrophic yeast Pichia pinus defective in C2 metabolism
Authors: Tolstorukov I. I. , Efremov B. D. , Benevolensky S. V. , Titorenko V. I. , Sibirny A. A.
Published: May 2005

A collection of mutants of Pichia pinus which are unable to grow on ethanol but retain the ability to grow on glucose and methanol, was obtained. Genetic and biochemical analysis of these strains revealed mutations in seven nuclear genes affecting activities of isocitrate lyase (icl1), malate synthase (mls1), phosphoenolpyruvate carboxykinase (pck1), ‘malic’ enzyme (mdd1) and acetyl‐CoA synthetase (acs1, acs2 and acs3). All mutations except acs1‐acs3 have no effect on the activities of other enzymes involved in C2 metabolism. Mutations acs1, acs2 and acs3 have a pleiotropic action, leading to partial reduction in activities of isocitrate lyase and malate synthase. Ethanol‐induced repression of the synthesis of the methanol oxidative enzymes, alcohol oxidase and catalase, is not impaired in these seven mutant classes. On the other hand, C2 compound‐induced inactivation of alcohol oxidase and catalase is impaired in mutants acs1, acs2, acs3 and icl1. It was suggested that glyoxylate and acetate (or acetate precursors) act as low molecular weight effectors, ‘switching on’ inactivation and repression, respectively, of alcohol oxidase and catalase in the medium containing ethanol or acetate.
Functional exploration of the yeast (Saccharomyces cerevisiae) genome: Use of a mini‐mu transposon to analyse randomly cloned DNA sequences
Authors: Daignan‐Fornier Bertrand , Bolotin‐Fukuhara Monique
Published: May 2005

The development of mega‐sequencing techniques requires new methods for global functional analysis of cloned DNA fragments. We have developed a mini‐Mu transposon adapted to yeast cloned DNA fragment analysis. This transposon allows us to do the following in a single construction: (i) to probe yeast cells for the presence of expressed open reading frames (ORFs) in the cloned DNA fragment; (ii) to localize these ORFs in the fragment and determine their transcription orientation; (iii) to use β‐galactosidase protein fusions to study regulation of these ORFs; and (iv) to disrupt the corresponding chromosomal genes.

On a 5‐kb yeast DNA sequence, we have verified the reliability of this new tool by comparing the data obtained with the mini‐Mu transposon to those obtained by classical methods.

This transposon should be of immediate use in the yeast genome sequencing programme.
Similar and different domains of chitin synthases 1 and 2 of S. cerevisiae: Two isozymes with distinct functions
Authors: Silverman Sanford J.
Published: May 2005

Saccharomyces cerevisiae produces two chitin synthases (Chs1 and Chs2) encoded by separate genes. Although these enzymes catalyze the same reaction, Chs2 is essential for septum formation whereas Chs1 has a repair function. To determine if these physiological differences are reflected in the enzyme structures, the CHS2 gene was sequenced and compared to that of CHS1. The predicted amino acid sequence of Chs2 shares substantial similarity with that of Chs1 in the carboxyl two‐thirds of the protein. The amino one‐third segments differ in predicted isoelectric point by almost 5 pH units. It is suggested that the similar regions are related to common catalytic function. The unrelated regions may be involved in regulation or localization of the respective enzymes. CHS1 and CHS2 are unlinked but may have arisen from the duplication of an ancestral gene.
Isolation and characterization of a hexokinase mutant of Schwanniomyces castellii: Consequences on cell production in continuous culture
Authors: Boze Hélène , Moulin G. , Galzy P.
Published: May 2005

A mutant of Schwanniomyces castellii with reduced glucose phosphorylation and with practically no phosphorylation of fructose was investigated. Carbon catabolite represion of α‐glucosidase and amylases was reduced. Repression of β‐galactosidase was normal. We have compared in continuous culture this mutant strain with wild type and another previously described mutant. The relationship between the specific rate of glucose consumption (Qs) and residual glucose concentration (s) in an inverse mode, suggests that there may be two types of transport of glucose. Mutation at the phosphorylation level causes apparent modification of the kinetic parameters of glucose uptake rate. The consequence of mutation at the phosphorylation level on biomass production was discussed.
Isolation, DNA sequence and regulation of a new cell division cycle gene from the yeast Saccharomyces cerevisiae
Authors: Hasegawa Hitoshi , Sakai Akira , Sugino Akio
Published: May 2005

A new complementation group of temperature‐sensitive mutants of the yeast Saccharomyces cerevisiae (ts26‐1 and ts26‐2) has been isolated and characterized. This mutation maps at 40·7 cM from arg8 and 48·9 cM from arg1 on the left arm of chromosome XV of yeast, providing that it is a newly identified gene. The dumbbell‐shape terminal morphology of the mutant cells at the restrictive temperatures is a characteristic of mutants defective in DNA replication. To study the defect of macromolecule synthesis in the mutant cells, DNA, RNA, and protein synthesis were measured at both permissive and restrictive temperatures. The data suggest that the primary defect of this mutation is at the initiation step of DNA synthesis.

The gene has been cloned from an S. cerevisiae genomic library by rescue of the conditional lethality of the mutants. It is present as a single copy in the haploid genome. DNA–RNA hybridization of the gene has identified 1 kb RNA, which is under cell‐division‐cycle control. DNA sequence analysis of the gene has identified an open reading frame capable of encoding a protein of molecular weight 25 055 (214 amino acids).
Isolation and sequence analysis of a K. lactis chromosomal DNA element able to autonomously replicate in S. cerevisiae and K. lactis
Authors: Fabiani Lucia , Aragona Maria , Frontali Laura
Published: May 2005

We have undertaken a search for autonomously replicating (ARSs) from Kluvermyces lactis chromosomal DNA able to sustain plasmid replication in K. lactis and in Saccharomyces cerevisiae. The discovery of such sequences might be interesting for the comparison of ARSs from different sources and possibly useful for the construction of multivalent vectors.

HindIII fragments from K. lactis chromosomal DNA were inserted in the YIp5 plasmid (lacking an origin of replication) and the resulting chimaeric plasmids were selected for the ability to transform S. cerevisiae. Four plasmids were identified and further analysed. Two contained the same 1.8 kb K. lactis fragment and transformed both K. lactis and S. cerevisiae with the same efficiency and stability, whereas the third transformed only S. cerevisiae and the fourth transformed K. lactis with a higher efficiency than S. cerevisiae. A detailed study was performed on the 1.8kb fragment which exhibited ARS function in both yeasts. The fragment was subcloned using different restriction enzymes and Bal31 exonuclease. Subclones were tested for ARS function. ARS activities in the two yeasts were localized in the same 100 bp region. Sequencing demonstrated the presence in this region of the dodecanucleotide 5′ATTTATTGTTTT 3′ differing from the ARS core consensus of S. cerevisiae only by a T insertion.

A similar nucleotide sequence of S. cerevisiae only in the putative replication origin of the 2 μ‐like plasmid pkD1 which stably replicates in K. lactis. Homologies with ARSs from S. cerevisiae were also found in the regions flanking the above‐mentioned dodecanucleotide.
Liposome‐mediated introduction of proteins into protoplasts of the yeast Hansenula polymorpha as a possible tool to study peroxisome biogenesis
Authors: Douma A. C. , Veenhuis M. , Driessen A. J. M. , Harder W.
Published: May 2005

Low pH‐induced fusion between liposomes and protoplasts of the yeast Hansenula polymorpha was demonstrated using a fluorescent assay and freeze‐etch techniques. By this method foreign proteins could be introduced into the cytosol of the protoplast. For instance, after fusion of glucose oxidase‐containing liposomes with protoplasts, activity of this enzyme was demonstrated cytochemically in the cytosol of the resulting protoplasts. Similar results were obtained when ferritin‐containing liposomes were used. Incorporation of foreign proteins into liposomes was not a prerequisite for their introduction into the cytosol of protoplasts. In experiments where ferritin was added to protoplast suspensions together with empty liposomes, this protein was also delivered to the protoplast cytosol. However, in the absence of liposomes no uptake of proteins occurred.

We tested the potential of this system in our studies on peroxisome biogenesis. Protoplasts of glucose‐grown H. polymorpha remained stable for prolonged periods in osmotically stabilized cultivation media. Peroxisomes in such protoplasts were capable of protein import and assembly of matrix proteins as was demonstrated by the 20‐fold increase in catalase activity after incubation with methanol or ethanol. However, mature alcohol oxidase purified from H. polymorpha introduced into protoplasts of glucose‐grown cells of this organism was not targeted to peroxisomes as demonstrated with (immuno)cytochemical techniques. The enzyme remained present in the cytosol while its activity gradually decreased. Therefore mature alcohol oxidase probably does not expose the right topogenic signal(s) for recognition by its target organelle.
Creation of ARS activity in yeast through iteration of non‐functional sequences
Authors: Zweifel Stephan G. , L. Fangman Walton
Published: May 2005

Replication origins in Saccharomyces cerevisiae have been identified through the clonning of autonomous replication sequence (ARS) elements that allow the extrachromosonal maintenance of plasmid molecules. ARS activity requires a close matcht to an 11 bp consensus sequence and A+T‐rich flanking DNA. ARS elements with a wide range of capacities for promoting plasmid maintenance have been described. We determined the ARS activity of plasmid with inserts consisting of repetitions of a 64 bp 100% A+T sequence that has sequence similarities to known ARS elements. An insert with approximately four repeats did not yield transformants, but inserts with either eight or eleven repeats did. The cooperative of ARS activity did not require a contiguous arrangement since a plasmid containing two inserts of four repeats each, separated by about 1 kb, was functional. Our results show that a charge from non‐function to function can be accomplished by the cumulative action of individually inactive sequences. We conclude that the probability of replication initiation is too low with only four repeats to allow plasmid maintenance, but the overall probability is increased by further sequence iteration to provide origin activity. We suggest that chromosomes may contain streches with dispersed, weak origin elements, each undetected by the conventional ARS assay, that in sum provide origin function.
Analysis of the THR4 region on chromosome III of the yeast Saccharomyces cerevisiae
Authors: Mannhaupt Gertrud , Van Der Linden Gerard , Vetter Irene , Maurer Kick , Pilz Ursula , Planta Rudi , Feldmann Horst
Published: May 2005

The gene encoding theonine synthase (THR4) from the yeast Saccharomyces cerevisiae was cloned by complementation of a thr4 mutant. This gene was also found on a lambda clone (5239) consisting of a fragment of chromosome III inserted in the vector lambda MG3. The THR4 gene encodes a protein of 514 amino acids (M.W. 58 kDa), which has extensive homologies with E. coli threonine synthase (thrC) and B. subtilis threonine synthase. The 5′ flanking region of the gene contains three regulatory sequences. [TGACT(C)] for the general amino acid control (GCN).

About 130 bp downstream of the THR4 gene another open reading frame (563 amino acids) is found in the opposite orientation. This may imply that this open reading frame, called CTR86, shares a terminator region with THR4. The function of the protein encoded by CTR86 is not yet clear, but the fact that the upstream region contains a GCN4 responsive site that the gene product may also be involved in amino acid biosynthesis.
The yeast regulatory gene PHO4 encodes a helix‐loop‐helix motif
Authors: Berben Gilbert , Legrain Michèle , Gilliquet Véronique , Hilger François
Published: May 2005

Evidence is presented, based on sequence comparisons and secondary structure prediction, of the presence of a DNA‐binding and dimerization helix‐loop‐helix motif in the yeast transcription activator PHO4. Interest in the existence of this first known motif in yeast is discussed.
Ornithine decarboxylase in Saccharomyces cerevisiae: Chromosomal assignment and genetic mapping of the SPE1 gene
Authors: Xie Qiao‐Wen , Tabor Celia White , Tabor Herbert
Published: May 2005

The gene for ornithine decarboxylase in Saccharomyces cerevisiae, SPE1, has been assigned to chromosome XI by the technique of transverse alternating pulsed field electrophoresis and DNA–DNA hybridization. Genetic mapping by tetrad analysis shows that the SPE1 gene is located on the left arm of chromosome XI, 6 cM from the LAP1 gene and 43 cM from the TRP3 gene. The spe10 mutation previously isolated in this laboratory is mapped to the N‐terminal region of the SPE1 gene, and therefore should be designated as a spe1 allele.