AILV1 gene from the yeast Arxula adeninivorans LS3 ­ a new selective transformation marker

The ILV1 gene of the yeast Arxula adeninivorans LS3 (AILV1) has been cloned from a genomic library, characterized and used as an auxotrophic selection marker for transformation of plasmids into this yeast. One copy of the gene is present in the Arxula genome, comprising 1653 bp and encoding 550 amino acids of the threonine deaminase. The protein sequence is similar (60·55%) to that of the threonine deaminase from Saccharomyces cerevisiae encoded by the gene ILV1. The protein is enzymatically active during the whole period of cultivation, up to 70 h. Maximal activities, as well as protein concentrations of this enzyme, were achieved after cultivation times of 20–36 h. The AILV1 gene is a suitable auxotrophic selection marker in transformation experiments using an Arxula adeninivorans ilv1 mutant and a plasmid containing this gene, which is fused into the 25S rDNA of Arxula adeninivorans. One to three copies of the linearized plasmid were integrated into the 25S rDNA by homologous recombination. Transformants resulting from complementation of the ilv1 mutation can be easily and reproducibly selected and in addition are mitotically stable. Therefore, the described system is preferred to the conventional selection for hygromycin B resistance. © 1998 John Wiley & Sons, Ltd.     

Development and evaluation of methods for determining the pattern of functionalization in sodium carboxymethylcelluloses

Sodium carboxymethylcellulose (NaCMC) with varying degrees of substitution (DS) was investigated with different analytical methods in order to characterize the functional group distribution. The following methods were tested and adapted: high-resolution ¹³C NMR spectroscopy in the solid state (¹³C CP/MAS NMR) and ¹³C NMR spectroscopy on solutions of NaCMC samples with a reduced molar mass. Partial degradation was accomplished by ultrasonic means and with the enzyme endoglucanase. Combining the two techniques resulted in the greatest reduction in molar mass and hence in the best spectral resolution. Analysis of the NaCMC fragments following ultrasonic and/or endoglucanase degradation also reveals another interesting experimental finding. It appears that ultrasonic degradation is favored at unsubstituted areas near the center of the chain. These methods were compared with the following already familiar techniques of analysis: titrimetric techniques; ¹³C and ¹H NMR spectroscopy as well as HPLC on completely hydrolysed solutions (hydrolysis with perchloric acid, trifluoroacetic acid and sulfuric acid). All of the methods characterize the samples as a series with increasing DS, the values of which range from 0.9 to 2.4. Methods that permit analysis of the partial degree of substitution produced the distribution x₂ > x₆ > x₃. Therefore, they are in principle suited for determining the functionalization pattern of the NaCMC samples relative to one another. The most suitable method can therefore be selected according to the objectives and the apparatus available. However, the measured values do exhibit considerable spread, variances of approx. 20%, thus, place restrictions on using the values of DS or x_i in absolute comparisons beyond these methods.     

A set of genetic markers for the chromosomes of the imperfect yeast Arxula adeninivorans

The nuclear genome of the anamorphic yeast Arxula adeninivorans was analysed by benomyl-induced haploidization of parasexual hybrids marked with 32 auxotrophic mutations and pulsed field gel electrophoresis followed by DNA hybridization. Twenty-seven genes have been arranged into four linkage groups by haploidization, 15 genes belong to group 1, six to group 2, and three each to groups 3 and 4. Five genes could be localized by DNA hybridization on three out of four separated chromosomes. The gene LYS2 of the largest linkage group 1 and the 25S rDNA were identified on the largest chromosome, the GAA and the TEF1 gene on chromosome 2, and the ILV1 gene of linkage group 4 on the smallest chromosome.     

Surface acoustic wave properties of natural smooth ultra-nanocrystalline diamond characterized by laser-induced SAW pulse technique

Diamond is one of the best SAW substrate candidates due to its highest sound velocity and thermal conductivity. But conventional diamond films usually express facet structure with large roughness. Ultra-nanocrystallined diamond (UNCD) films grown in a 2.45 GHz IPLAS microwave plasma enhanced chemical vapor deposition (MPECVD) system on Si (100) substrates in CH₄-Ar plasma possess naturally smooth surface and are advantageous for device applications. Moreover, highly C-axis textured aluminum nitride (AlN) films can be grown by DC-sputtering directly on UNCD coated Si substrate. However, properties of UNCD films are much complex than microcrystalline diamond films, that is because this is a very complex material system with large but not fixed portion of grain boundaries and sp²/sp³ bonding. Properties of UNCD films could change dramatically with similar deposition condition and with similar morphologies. A simple and quick method to characterize the properties of these UNCD films is important and valuable. Laser-induced SAW pulse method, which is a fast and accurate SAW properties measuring system, for the investigation of mechanical and structure properties of thin films without any patterning or piezoelectric layer.     

Piezoelectric GaN sensor structures

Free-standing GaN and AlGaN/GaN cantilevers have been fabricated on (111) silicon substrate using dry etching. On these cantilevers, a piezoresistor and a high-electron-mobility transistor (HEMT) structure have been realized, and the piezoresponse has been characterized. Cantilever bending experiments resulted in a Young's modulus of approximately 250 GPa, a sensitivity of K/spl sim/90, and a modulation of the HEMT current of up to 50%. It is seen that the piezoresponse could be related to both the bulk properties and the properties of the heterostructure interface.     

AILV1 gene from the yeast Arxula adeninivorans LS3--a new selective transformation marker

The ILV1 gene of the yeast Arxula adeninivorans LS3 (AILV1) has been cloned from a genomic library, characterized and used as an auxotrophic selection marker for transformation of plasmids into this yeast. One copy of the gene is present in the Arxula genome, comprising 1653 bp and encoding 550 amino acids of the threonine deaminase. The protein sequence is similar (60.55%) to that of the threonine deaminase from Saccharomyces cerevisiae encoded by the gene ILV1. The protein is enzymatically active during the whole period of cultivation, up to 70 h. Maximal activities, as well as protein concentrations of this enzyme, were achieved after cultivation times of 20-36 h. The AILV1 gene is a suitable auxotrophic selection marker in transformation experiments using an Arxula adeninivorans ilv1 mutant and a plasmid containing this gene, which is fused into the 25S rDNA of Arxula adeninivorans. One to three copies of the linearized plasmid were integrated into the 25S rDNA by homologous recombination. Transformants resulting from complementation of the ilv1 mutation can be easily and reproducibly selected and in addition are mitotically stable. Therefore, the described system is preferred to the conventional selection for hygromycin B resistance.     

In situ STM study of the effect of chlorides on the initial stages of anodic oxidation of Cu(111) in alkaline solutions

In situ electrochemical scanning tunneling microscopy (STM) has been applied to study the mechanisms of growth of passive layers on Cu(111) in NaOH solutions in the presence of chlorides. For [Cl⁻]/[OH⁻]=0.01, the same ordered precursor phase of adsorbed OH is observed in the underpotential region of oxidation as in Cl⁻-free solutions. Atomically resolved images reveal the structure of the reconstructed topmost metal plane and the threefold hollow adsorption site of the hydroxide. The induced reconstruction causes the ejection of Cu atoms that contribute to the observed lateral growth of the terraces and to the formation of 2D Cu ad-islands in the final stages of the adsorption process. For [Cl⁻]/[OH⁻]=0.1, threadlike nanostructures resulting from the reaction of the ejected Cu atoms with chlorides are formed before agglomeration with the 2D Cu ad-islands formed in the final stage of the hydroxide adsorption process. For [Cl⁻]/[OH⁻]=10, the step edges, which are normally the preferential sites of the reaction with hydroxide, are blocked by the formation of non-ordered surface chloride complexes. Hydroxide adsorption still predominates the surface reaction on the terraces but the 2D ad-islands form immediately due to the blocking of the step edges. In the potential range of Cu(I) oxide formation, crystalline Cu(I) oxide layers are formed with a high density of steps and (111) terraces. Their step edges are rougher in the presence of chlorides which indicates a Cl⁻-enhanced localized dissolution reaction of the oxide layers at step edges.     

Study of Spin-Valve Operation in Permalloy–SiO2–Silicon Nanostructures

Magnetotransport studies are performed on nanoscale Permalloy(Py)–(Mg)–SiO₂-degenerate Si(100) tunneling devices in spin-valve geometry with and without Mg interlayer. Highly remanent, single domain Py electrodes (15–100-μm length, 100–1000-nm width) are realized by electron-beam lithography, electron-beam evaporation, and subsequent lift-off. Different widths ensure subsequent switching of the Py nanoelectrodes in increasing magnetic fields. A suppression of spin-polarized current is expected for antiparallel magnetization configuration of source and drain contacts (i.e. positive magnetoresistance) if spin injection and detection have been successfully implemented. Magnetic hysteresis curves of Py nanowire arrays measured at temperatures from 5 K up to 300 K reveal increasing coercive fields (up to 40 mT) for decreased nanowire widths as required for device operation. Small positive magnetoresistance is observed for the spin-valve geometry with Mg interlayer at 4.2 K, contrary to the negative anisotropic magnetoresistance measured of single wires.