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  • 1
    Electronic Resource
    Electronic Resource
    Aromatic amino-acid biosynthesis in Candida albicans: identification of the ARO4 gene encoding a second DAHP synthase (1996)
    Springer
    Current genetics 29 (1996), S. 441-445 
    Details
    ISSN: 1432-0983
    Keywords: Key words  Aromatic amino-acid biosynthesis ; 3-deoxy-d-arabinoheptulosonate-7-phosphate synthase ; Aro3p/Aro4p ; 5-fluoroorotic acid ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract   The primary step in the aromatic amino-acid biosynthetic pathway in Saccharomyces cerevisiae is catalyzed by two redundant isozymes of 3-deoxy-d-arabinoheptulosonate-7-phosphate (DAHP) synthase, either of which alone is sufficient to permit growth on synthetic complete media lacking aromatic acids (SC-Aro). The activity of one isozyme (encoded by the ARO3 gene) is feedback-inhibited by phenylalanine, whereas the activity of the other isozyme (encoded by the ARO4 gene) is feedback-inhibited by tyrosine. Transcription of both genes is controlled by GCN4. We previously cloned the ARO3 gene from the opportunistic pathogen Candida albicans and found that: (1) it can complement an aro3 aro4 double mutation in S. cerevisiae, an effect inhibited by excess phenylalanine; and (2)  its expression is induced in response to amino-acid deprivation, consistent with the presence of two putative GCN4-responsive promoter elements (Pereira and Livi 1993, 1995). To determine whether other DAHP synthases exist in C. albicans, we have constructed a homozygous aro3-deletion mutant strain. Such a mutant was found to be phenotypically Aro+, i.e., capable of normal growth on SC-Aro media, suggesting the presence of at least one additional isozyme. To confirm this result, a 222-bp DNA fragment was amplified by the polymerase chain reaction (PCR) from genomic DNA prepared from the homozygous aro3-deletion mutant, using a degenerate primer based on a conserved N-terminal region of Aro3p plus a degenerate comeback primer encoding a conserved region of the protein that lies within the deleted portion of the gene. The nucleotide sequence of this PCR fragment predicts a 74-amino acid DAHP synthase-related protein which shows strong homology to Aro3p from S. cerevisiae and C. albicans, but even greater homology (78% identity) to S. cerevisiae Aro4p. We conclude that cells of C. albicans contain a second Aro4p-related DAHP synthase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002940050069
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  • 2
    Electronic Resource
    Electronic Resource
    Pinning of daisy modes in optically pumped vertical-cavity surface-emitting lasers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2239-2241 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed stable single-mode oscillation of optically pumped vertical-cavity surface-emitting lasers (i.e., without fabricated aperture) in several high-order daisy modes. The surprising stability of the nodal lines of a daisy mode is explained as being due to the combined action of many microscopic defects; when a daisy mode is moved across the wafer, the effective correlation length of the orientation of the pinning is of the order of 1 μm. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121688
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  • 3
    Electronic Resource
    Electronic Resource
    Interpretation of double x-ray diffraction peaks from InGaN layers (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 1432-1434 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The presence of two, or more, x-ray diffraction (XRD) peaks from an InGaN epilayer is sometimes regarded as an indicator of phase segregation. Nevertheless, detailed characterization of an InGaN/GaN bilayer by a combination of XRD and Rutherford backscattering spectrometry (RBS) shows that splitting of the XRD peak may be completely unrelated to phase decomposition. Wurtzite InGaN/GaN layers were grown in a commercial reactor. An XRD reciprocal space map performed on the (105) plane shows that one component of the partially resolved InGaN double peak is practically aligned with that of the GaN buffer, indicating that part of the layer is pseudomorphic to the GaN template. The other XRD component is shown to have the same indium content as the pseudomorphic component, from a consideration of the effect of strain on the c- and a-lattice constants. The composition deduced from XRD measurements is confirmed by RBS. Depth-resolving RBS channeling angular scans also show that the region closer to the GaN/InGaN interface is nearly pseudomorphic to the GaN substrate, whereas the surface region is almost fully relaxed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1397276
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  • 4
    Electronic Resource
    Electronic Resource
    Erratum: "Interpretation of double x-ray diffraction peaks from InGaN layers" [Appl. Phys. Lett. 79, 1432 (2001)] (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 337-337 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1430029
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  • 5
    Electronic Resource
    Electronic Resource
    Compositional dependence of the strain-free optical band gap in InxGa1−xN layers (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2137-2139 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of strain on the compositional and optical properties of a set of epitaxial single layers of InxGa1−xN was studied. Indium content was measured free from the effects of strain by Rutherford backscattering spectrometry. Accurate knowledge of the In mole fraction, combined with x-ray diffraction measurements, allows perpendicular strain (εzz) to be evaluated. Optical band gaps were determined by absorption spectroscopy and corrected for strain. Following this approach, the strain free dependence of the optical band gap in InxGa1−xN alloys was determined for x≤0.25. Our results indicate an "anomalous," linear, dependence of the energy gap on the In content, at room temperature: Eg(x)=3.39–3.57x eV. Extension of this behavior to higher concentrations is discussed on the basis of reported results. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1358368
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  • 6
    Electronic Resource
    Electronic Resource
    Structural and optical properties of InGaN/GaN layers close to the critical layer thickness (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 1207-1209 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work, we investigate structural and optical properties of metalorganic chemical vapor deposition grown wurtzite InxGa1−xN/GaN epitaxial layers with thicknesses that are close to the critical layer thickness (CLT) for strain relaxation. CLT for InxGa1−xN/GaN structures was calculated as a function of the InN content, x, using the energy balance model proposed by People and Bean [Appl. Phys. Lett. 47, 322 (1985)]. Experimentally determined CLT are in good agreement with these calculations. The occurrence of discontinuous strain relaxation (DSR), when the CLT is exceeded, is revealed in the case of a 120 nm thick In0.19Ga0.89N layer by x-ray reciprocal space mapping of an asymmetrical reflection. The effect of DSR on the luminescence of this layer is clear: The luminescence spectrum shows two peaks centered at ∼2.50 and ∼2.67 eV, respectively. These two components of the luminescence of the sample originate in regions of different strain, as discriminated by depth-resolving cathodoluminescence spectroscopy. DSR leads directly to the emergence of the second, lower-energy, peak. Based on this experimental evidence, it is argued that the appearance of luminescence doublets in InGaN is not evidence of "quantum dotlike In-rich" or "phase separated" regions, as commonly proposed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1499220
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  • 7
    Electronic Resource
    Electronic Resource
    Comment on "Low Stokes shift in thick and homogeneous InGaN epilayers" [Appl. Phys. Lett. 80, 550 (2002)] (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 1353-1354 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1498003
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  • 8
    Electronic Resource
    Electronic Resource
    Cytosolic localization in tomato mesophyll cells of a novel glutamine synthetase induced in response to bacterial infection or phosphinothricin treatment (1998)
    Springer
    Planta 206 (1998), S. 426-434 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Glutamine synthetase ; Lycopersicon ; Nitrogen remobilization ; Phosphinothricin ; Plant defense ; Pseudomonas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. In tomato (Lycopersicon esculentum Mill.) leaves, the predominant glutamine synthetase (GS; EC 6.3.1.2) is chloroplastic (GS2; 45 kDa) whereas the cytosolic isoform (GS1; 39 kDa) is represented as a minor enzyme. Following either infection by Pseudomonas syringae pv. tomato (Pst) or treatment with phosphinothricin (PPT), a GS inhibitor, GS1 accumulated in the leaves. In contrast to healthy control leaves, where GS1 was restricted to the veins, in infected and PPT-treated leaves the GS1 polypeptide was also detected in the leaf blade; moreover, it was more abundant than GS2. Different immunological approaches were therefore used to investigate whether or not the GS1 polypeptide expressed in Pst-infected and PPT-treated tomato leaves was distributed among different tissues and subcellular compartments in the same way as the constitutive GS1 expressed in healthy leaves. By tissue-printing analysis, a similar GS immunostaining was observed in epidermis, mesophyll and phloem of leaflet midrib cross-sections of control, infected and PPT-treated leaves. Immunocytochemical localization revealed that GS protein was present in the chloroplast of mesophyll cells and the cytoplasm of phloem cells in healthy leaves; however, in Pst-infected or PPT-treated leaves, a strong labelling was observed in the cytoplasm of mesophyll cells. Two-dimensional analysis of GS polypeptides showed that, in addition to the constitutive GS1, a GS1 polypeptide different in charge was present in tomato leaflets after microbial infection or herbicide treatment. All these results indicate that a novel cytosolic GS is induced in mesophyll cells of Pst-infected or PPT-treated leaves. A possible role for this new cytosolic GS in the remobilization of leaf nitrogen during infection is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050418
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  • 9
    Electronic Resource
    Electronic Resource
    Diversity of prokaryotic chromosomal proteins and the origin of the nucleosome (1998)
    Springer
    Cellular and molecular life sciences 54 (1998), S. 1350-1364 
    Details
    ISSN: 1420-9071
    Keywords: Key words. DNA packaging; nucleoid; macromolecular crowding; Archaea; histone; nucleosome; chromatin.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. All cells employ architectural proteins to confine and organize their chromosomes, and to prevent the otherwise thermodynamically favored collapse of concentrated DNA into compact structures. To accomplish this, prokaryotes have evolved a variety of phylogenetically unrelated, small, basic, sequence-independent DNA-binding proteins that include histones in Euryarchaeota, and members of the HU family in many Bacteria. In contrast, virtually all Eukarya employ histones, and recently a metabolism-based hypothesis proposed that the eukaryal nucleus originated from a hydrogen-consuming, histone-containing Archaeon. Histones may have prevailed during the evolution of the Eukarya because of their extended interactions with DNA and, as noted, the histone fold now exists not only in histones but also as a structural motif in eukaryal transcription factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000180050259
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  • 10
    Electronic Resource
    Electronic Resource
    Realization of the Einstein-Podolsky-Rosen paradox for continuous variables in nondegenerate parametric amplification (1992)
    Springer
    Applied physics 55 (1992), S. 265-278 
    Details
    ISSN: 1432-0649
    Keywords: 42.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Einstein-Podolsky-Rosen (EPR) paradox is demonstrated experimentally for continuous variables by employing a nondegenerate optical parametric amplifier (NOPA). Such a system is analogous to and under some ideal conditions is in one-to-one correspondence with the original system discussed by EPR. In particular, the quadrature-phase amplitudes for a signal beam are inferred in turn from those of a spatially separated but strongly correlated idler beam, where these optical amplitudes are analogous to canonical position and momentum variables. The variances for the two inferences are measured and their product is observed to be below the limit of unity associated with the Heisenberg uncertainty relation, in apparent contradiction with quantum mechanics according to the argument of EPR. The smallest product of inference variances achieved in the experiment is (0.70±0.01). Various other types of quantum noise for this system are also investigated, and a theory of a narrowband NOPA is presented with losses included. A comparison between experiment and this theory shows relatively good agreement. The question of a local hidden-variables description of the system is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00325015
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