Home About us Contact
|
Home About us Contact | ||
|
|
||
Domain Structure (domain + structure)
Selected AbstractsDomain structure and miscibility studies of blends of styrene,butadiene,styrene block copolymers (SBS) and styrene,glycidyl methacrylate statistical copolymers (PS-GMA) using SAXS and DMTAPOLYMER INTERNATIONAL, Issue 3 2007LB Canto Abstract The domain structure and miscibility in the solid state of a series of blends of styrene-butadiene-styrene (SBS) block copolymers and styrene-glycidyl methacrylate (PS-GMA) statistical copolymers with varying molecular weights and compositions were studied using small angle X-ray scattering and dynamic mechanical thermal analysis. Depending on the molecular characteristics of each component, different types and degrees of solubilization of PS-GMA in SBS were found which, in addition to the initially SBS phase morphology, lead to materials with multiphase domain morphologies with differences in size and structure. The degree of solubilization of PS-GMA into the PS domains of SBS was found to be higher for blends containing PS-GMA with lower molecular weight (Mw = 18 100 g mol,1) and lower GMA content (1 wt%) and/or for SBS with higher PS content (39 wt%) and longer PS blocks (Mw = 19 600 g mol,1). Localized solubilization of PS-GMA in the middle of PS domains of SBS was found to be the most probable to occur for the systems under study, causing swelling of PS domains. However, uniform solubilization was also observed for SBS/PS-GMA blends containing SBS with composition in the range of a morphological transition (PS block Mw = 19 600 g mol,1 and 39 wt% of PS) causing a morphological transition in the SBS copolymer (cylinder to lamella). Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd [source] Cloning of Xenopus orthologs of Ctf7/Eco1 acetyltransferase and initial characterization of XEco2FEBS JOURNAL, Issue 24 2008Masatoshi Takagi Sister chromatid cohesion is important for the correct alignment and segregation of chromosomes during cell division. Although the cohesin complex has been shown to play a physical role in holding sister chromatids together, its loading onto chromatin is not sufficient for the establishment of sister chromatid cohesion. The activity of the cohesin complex must be turned on by Ctf7/Eco1 acetyltransferase at the replication forks as the result of a specific mechanism. To dissect this mechanism in the well established in vitro system based on the use of Xenopus egg extracts, we cloned two Xenopus orthologs of Ctf7/Eco1 acetyltransferase, XEco1 and XEco2. Both proteins share a domain structure with known members of Ctf7/Eco1 family proteins. Moreover, biochemical analysis showed that XEco2 exhibited acetyltransferase activity. We raised a specific antibody against XEco2 and used it to further characterize XEco2. In tissue culture cells, XEco2 gradually accumulated in nuclei through the S phase. In nuclei formed in egg extract, XEco2 was loaded into the chromatin at a constant level in a manner sensitive to geminin, an inhibitor of the pre-replication complex assembly, but insensitive to aphidicolin, an inhibitor of DNA polymerases. In both systems, no specific localization was observed during mitosis. In XEco2-depleted egg extracts, DNA replication occurred with normal kinetics and efficiency, and the condensation and sister chromatid cohesion of subsequently formed mitotic chromosomes was unaffected. These observations will serve as a platform for elucidating the molecular function of Ctf7/Eco1 acetyltransferase in the establishment of sister chromatid cohesion in future studies, in which XEco1 and XEco2 should be dissected in parallel. [source] A novel NADPH-dependent oxidoreductase with a unique domain structure in the hyperthermophilic Archaeon, Thermococcus litoralisFEMS MICROBIOLOGY LETTERS, Issue 1 2008András Tóth Abstract Thermococcus litoralis, a hyperthermophilic Archaeon, is able to reduce elemental sulfur during fermentative growth. An unusual gene cluster (nsoABCD) was identified in this organism. In silico analysis suggested that three of the genes (nsoABC) probably originated from Eubacteria and one gene (nsoD) from Archaea. The putative NsoA and NsoB are similar to NuoE- and NuoF-type electron transfer proteins, respectively. NsoC has a unique domain structure and contains a GltD domain, characteristic of glutamate synthase small subunits, which seems to be integrated into a NuoG-type sequence. Flavin and NAD(P)H binding sites and conserved cysteines forming iron,sulfur clusters binding motifs were identified in the protein sequences deduced. The purified recombinant NsoC contains one FAD cofactor per protein molecule and catalyzes the reduction of polysulfide with NADPH as an electron donor and it also reduces oxygen. It was concluded that the Nso complex is a new type of NADPH-oxidizing enzyme using sulfur and/or oxygen as an electron acceptor. [source] Adherence factors of Lactobacillus in the human gastrointestinal tractFEMS MICROBIOLOGY LETTERS, Issue 2 2007Mónica Perea Vélez Abstract Despite the increasing number of scientific reports describing adhesion of Lactobacillus to components of the human intestinal mucosa, information on the surface molecules mediating this adhesion and their corresponding receptors is fragmentary. This MiniReview compiles present knowledge of the genetically and functionally characterized Lactobacillus factors responsible for mediating adhesion to different components of the human gastrointestinal tract. In addition, for the proteins among these factors, the domain structure is discussed, and where appropriate the results of in silico analyses are reported. [source] Block Copolymer Nanostructures: Nanoscopic Morphologies in Block Copolymer Nanorods as Templates for Atomic-Layer Deposition of Semiconductors (Adv. Mater.ADVANCED MATERIALS, Issue 27 200927/2009) The frontispiece shows a TEM image of block copolymer nanorods exhibiting nanoscopic domain structures visualized by selective staining. The insets represent the methodology for producing semiconductor nanostructures reported by Yong Wang, Martin Steinhart, and co-workers on p. 2763. The first panel shows block copolymer nanorods, the second, the nanorods after conversion of the nanoscopic domain structure into a mesopore structure, and the third, the complex 1D semiconductor nanostructures obtained by ALD using the mesopores as templates. [source] Tracking reflections through cryogenic cooling with topographyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2006Jeffrey J. Lovelace The mosaic structure of a single protein crystal was analyzed by reflection profiling and topography using highly parallel and monochromatic synchrotron radiation. Fine-,-sliced diffraction images (0.002° stills) were collected using a conventional large-area CCD detector in order to calculate reflection profiles. Fine-,-sliced topographic data (0.002°) stills were collected with a digital topography system for three reflections in a region where the Lorentz effect was minimized. At room temperature, several different mosaic domains were clearly visible within the crystal. Without altering the crystal orientation, the crystal was cryogenically frozen (cryocooled) and the experiment was repeated for the same three reflections. Topographs at cryogenic temperatures reveal a significantly increased mosaicity, while the original domain structure is maintained. A model for the observed changes during cryocooling is presented. [source] Influence of the copolymer architecture and composition on the response and mechanical properties of pH-sensitive fibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Anasuya Sahoo Abstract A series of copolymers based on acrylonitrile (AN) and acrylic acid (AA) with varying architecture and composition were synthesized using free radical polymerization. The distribution of monomers in the copolymer chains could be successfully controlled by regulating the addition of more reactive monomer (AA). Copolymers having nearly random distribution of comonomer moieties to block type distribution with different composition (10,50 mol % AA) were synthesized to investigate the effect of polymer architecture and composition on pH response and mechanical properties of resultant structures. These copolymers were solution spun from dimethylformamide-water system, drawn in coagulation bath, and annealed at 120°C for 2 h to make pH-sensitive fibers which were structurally stable without the need of chemical crosslinking. The fibers from block copolymers showed significantly better tensile strength (34.3 MPa), higher retractive forces (0.26 MPa), and enhanced pH response (swelling 3890%) in comparison with fibers from random copolymer (13.55 MPa, 0.058 MPa, and 1723%, respectively). The tensile strength and retractive forces could be further improved to a value of 72 MPa and 0.36 MPa, respectively, by changing the composition of the block copolymer while retaining the swelling percentage similar to the random copolymer mentioned above. It is proposed that on processing to fibers, the block copolymers could form a segregated domain structure with separate domains of AA and AN, where AN domains were responsible for high structural integrity by providing connectivity among polymer chains, while AA domains showed improved response to changing pH of the environment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] The effects of graphical overviews on knowledge acquisition in hypertextJOURNAL OF COMPUTER ASSISTED LEARNING, Issue 2 2002T. De Jong Abstract A central aspect of designing hypertext for learning concerns the structure of the information in the hypertext and the view the learner is offered of this structure. In this study, a hypertext environment was enhanced with a graphical overview that represented the basic, inherent, structure of the domain and the layout was designed in such a way that learners were unobtrusively encouraged to follow a sequence of exploration that followed the domain structure. This so-called ,visual' lay-out was compared with two lay-outs that presented randomly positioned nodes. One of these two lay-outs contained hints (using ,highlighting') to stimulate learners to follow a domain related exploration similar to the one incorporated in the visual lay-out. The other (,control') lay-out did not provide such hints. Results showed that participants from both the ,visual' and the ,hints' conditions demonstrated a more domain-related exploration pattern than participants from the ,control' condition. Participants in the ,visual' lay-out did not show a better recall of the content of the nodes as such, but showed a significantly better acquisition of knowledge of structure than participants from the other two conditions. These data indicate that a visual display conveys knowledge in its own right and that knowledge gained does not depend on the exploration route followed in the hypertext material. [source] Expression of the basal cell adhesion molecule (B-CAM) in normal and diseased human skinJOURNAL OF CUTANEOUS PATHOLOGY, Issue 3 2000Thi-Mai Bernemann The basal cell adhesion molecule (B-CAM) is a 90-kD cell surface glycoprotein with a characteristic immunoglobulin domain structure. The pattern of B-CAM expression in cultured cells suggests that the molecule is associated with a substrate-adherent growth pattern in some lineages. We investigated the expression of B-CAM in normal and diseased human epidermis by means of immunohistochemistry employing a single batch of high-titer mouse monoclonal antibody G253. Snap-frozen biopsy material from normal skin (n=8), psoriasis (n=5), contact dermatitis (n=6), basal cell carcinoma (n=5) and fetal skin (n=6) was studied. In normal human skin, B-CAM was found in varying degrees throughout the epidermis with a preference for suprabasal expression, hair follicles were regularly of a B-CAM-positive phenotype. There were no qualitative differences with regard to the B-CAM expression pattern in normal skin in comparison to psoriasis and contact dermatitis. In contrast, fetal skin (15th to 18th week of gestation) was characterized by B-CAM-positive cells in the basal layer of the epidermis as well as in the outer root sheath of hair follicles. Basal cell carcinomas also regularly expressed high levels of B-CAM. A strong B-CAM-positive phenotype can be found in the outer root sheath of hair follicles of adult and fetal human skin as well as in fetal basal keratinocytes. [source] Near-field imaging of ultrathin magnetic films with in-plane magnetizationJOURNAL OF MICROSCOPY, Issue 3 2003W. Dickson Summary A new approach to near-field magneto-optical imaging was developed capable of visualization of in-plane magnetization of ultrathin magnetic structures. The approach relies on the magneto-optical effect specific for thin magnetic layers and employs near-field transmission measurements of longitudinal and/or transverse magneto-optical effect arising from the presence of thin film interfaces. The near-field magneto-optical contrast of in-plane domain structure of ultrathin Co film has been demonstrated in different polarization configurations. [source] Studies of the magnetic structure at the ferromagnet,antiferromagnet interfaceJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001A. Scholl Antiferromagnetic layers are a scientifically challenging component in magnetoelectronic devices, such as magnetic sensors in hard-disk heads, or magnetic random-access memory (RAM) elements. In this paper, it is shown that photoelectron emission microscopy (PEEM) is capable of determining the magnetic structure at the interface of ferromagnets and antiferromagnets with high spatial resolution (down to 20,nm). Dichroism effects at the L edges of the magnetic 3d transition metals, using circularly or linearly polarized soft X-rays from a synchrotron source, give rise to a magnetic image contrast. Images, acquired with the PEEM2 experiment at the Advanced Light Source, show magnetic contrast for antiferromagnetic LaFeO3, microscopically resolving the magnetic domain structure in an antiferromagnetically ordered thin film for the first time. Magnetic coupling between LaFeO3 and an adjacent Co layer results in a complete correlation of their magnetic domain structures. From field-dependent measurements, a unidirectional anisotropy resulting in a local exchange bias of up to 30,Oe in single domains could be deduced. The elemental specificity and the quantitative magnetic sensitivity render PEEM a perfect tool to study magnetic coupling effects in multilayered thin-film samples. [source] In Situ Transmission Electron Microscopy of Electric Field-Triggered Reversible Domain Formation in Bi-Based Lead-Free PiezoceramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Jens Kling A lead-free piezoelectric 0.91(Bi1/2Na1/2)TiO3,0.06BaTiO3,0.03(K0.5Na0.5)NbO3 ceramic with high strain was examined in situ under an applied electric field using the transmission electron microscope. No domain structure is observed without an electric field, but an alternating electric field leads to the reversible formation of a lamellar domain structure. Correlations to polarization and strain hysteresis loop measurements indicate an electric field-induced phase transition from a nonpolar to a ferroelectric state and vice versa. [source] Direct Scanning Electron Microscopy Imaging of Ferroelectric Domains After Ion MillingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Daniel Grüner A method for directly observing the ferroelectric domain structure by scanning electron microscopy after argon ion milling has been established. Its advantages are exemplified by exposing the domain structure in three widely used ferroelectric ceramics, BaTiO3, (Na,K)NbO3, and Pb(Ti,Zr)O3. Stable high-resolution images revealing domains with widths <30 nm have been obtained. The domain contrast is caused by electron channeling and is strongly dependent on the sample tilt angle. Owing to a strain- and defect-free surface generated by gentle ion milling, pronounced orientation contrast is observed. [source] Influence of Dipolar Fields on the Photochemical Reactivity of Thin Titania Films on BaTiO3 SubstratesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Nina V. Burbure The photochemical properties of TiO2 films supported on BaTiO3 were investigated to test the hypothesis that dipolar fields from a ferroelectric substrate would affect the reactivity of the supported film. Photochemical reaction products were formed on the TiO2 surface in patterns that correspond to the underlying domain structure of BaTiO3. As the film thickness increases from 10 to 100 nm, the titania more effectively screens the ferroelectric field, and the pattern of reaction products is obscured. It is concluded that dipolar fields from the ferroelectric substrate influence charge carrier transport in the film and spatially localize the reaction products. [source] Ordering Behavior of Layered Silicate Nanocomposites with a Cylindrical Triblock CopolymerMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2006Chung Ho Lee Abstract Summary: The ordering behavior of the nanocomposites of organically modified montmorillonite (OMMT) with a cylindrical triblock copolymer of polystyrene- block -poly(ethylene- co -butylene)- block -polystyrene (SEBS) has been investigated by temperature-resolved small-angle X-ray scattering (SAXS) and rheometry. X-Ray diffraction (XRD) confirms that the polymer chains are successfully intercalated with the interlayer gallery of the silicates. The data obtained from the SAXS and rheological measurements show that the addition of OMMT leads to a change in the microphase separation behavior of SEBS in the nanocomposites. The molecular interaction between OMMT and the polystyrene (PS) chains of SEBS decreases the structural perfection of the self-assembling, phase-separated domain structure of the nanocomposites. Rheological data exhibit that the order-order (TOOT) and order-disorder transitions (TODT) of the SEBS/OMMT nanocomposites decrease with the addition of OMMT. The highest elongation at break is obtained at approximately 2% OMMT and its further addition to the mixture leads to decreases in tensile strength and elongation. The change in the storage modulus (G,) of a) SEBS, b) S98M2, c) S95M5, and d) S90M10, as a function of temperature in the range of 150,,,T (°C),,,260. [source] A subset of GAF domains are evolutionarily conserved sodium sensorsMOLECULAR MICROBIOLOGY, Issue 2 2007Martin Cann Summary Most organisms maintain a transmembrane sodium gradient for cell function. Despite the importance of Na+ in physiology, no directly Na+ -responsive signalling molecules are known. The CyaB1 and CyaB2 adenylyl cyclases of the cyanobacterium Anabaena PCC 7120 are inhibited by Na+. A D360A mutation in the GAF-B domain of CyaB1 ablated cAMP-mediated autoregulation and Na+ inhibition. Na+ bound the isolated GAF domains of CyaB2. cAMP blocked Na+ binding to GAF domains but Na+ had no effect on cAMP binding. Na+ altered GAF domain structure indicating a mechanism of inhibition independent of cAMP binding. ,cyaB1 and ,cyaB2 mutant strains did not grow below 0.6 mM Na+ and ,cyaB1 cells possessed defects in Na+/H+ antiporter function. Replacement of the CyaB1 GAF domains with those of rat phosphodiesterase type 2 revealed that Na+ inhibition has been conserved since the eukaryotic/bacterial divergence. CyaB1 and CyaB2 are the first identified directly Na+ -responsive signalling molecules that function in sodium homeostasis and we propose a subset of GAF domains underpin an evolutionarily conserved Na+ signalling mechanism. [source] Magnetic pinning-effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 bilayerPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007Daniel Hsu Abstract The vortex lines of superconductor can be driven by electrical currents, which are often coupled with a reliable control of flux quanta movement by defects or magnetic domains. In this work, the magnetic pinning-effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 (NCMO/YBCO) bilayers is investigated. It is found that by increasing the field from 0 to 5 Tesla, the critical current Ic of pure YBCO film at 50 K is suppressed by three orders of magnitude. However, in the NCMO/YBCO bilayer Ic is less sensitive to the field and maintains at the level of 100 mA at high field. This result indicates that the magnetic pining effect of NCMO is much more efficient than the conventional routes, which maybe related to the fine domain structure of NCMO film. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characteristic magnetic length-scales in Vitroperm , Combining Kerr microscopy and small-angle neutron scatteringPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2004A. Grob Abstract We present a study of the magnetic-field dependence of the magnetic microstructure of the nanocrystalline soft magnet Vitroperm (Fe73Si16B7Nb3Cu1), which was treated so as to exhibit a macroscopic magnetic anisotropy. The samples were analysed using Kerr microscopy and small-angle neutron scattering (SANS). As the applied magnetic field is decreased starting from saturation, we find that two processes occur independently: the formation of a domain structure with the net magnetisation of the domains aligned along the macroscopic easy axis and the increase in magnitude of static, nanometer-scale fluctuations of the spin orientation. The domain structure observations from Kerr microscopy are in excellent agreement with the results of the SANS experiments. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature-induced changes of domain structures in ultrathin magnetic filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2006T. Polyakova Abstract We describe the thermal-driven evolution of stripe domain structures in ultrathin magnetic films with perpendicular anisotropy. Taking into account temperature dependencies of the film magnetic parameters we analyze possible temperature dependencies of the domain period. It is shown that the film heating leads to a decrease in the domain period. In soft films thermally assisted domain nucleation could provide a continuous decrease of the domain period while the domain structure passes through equilibrium states. On increasing the temperature of a hard film, the domain structure exists as metastable one adjusting its period by a sequence of jumps towards to equilibrium. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Extension rheology of liquid-crystalline solution/layered silicate hybridsPOLYMER ENGINEERING & SCIENCE, Issue 4 2010Gleb B. Vasilyev The extension rheology of polymer/layered silicate composites based on liquid-crystalline (LC) solution of hydroxypropylcellulose (HPC) in oligomeric polyethyleneglycole (PEG) was studied. The HPC concentration was 60 wt%. Extension experiments have been carried out for materials in the different phase states. Compositions containing Na-montmorillonite (MMT) were prepared by a two-stage method. Final systems may be attributed to solutions of HPC in PEG, which intercalates into MMT galleries. The ordered domain structure of the LC matrix as well as hydrogen-bonded network between HPC and PEG molecules significantly reduce deformation at break and provide a strong nonlinear viscoelastic behavior at extension. Appearance of isotropic phase in solutions leads to a sharp drop of the elongation viscosity. The introduction of clay into LC solution only slightly affects the viscosity value but significantly suppresses the strain-hardening scale. In contrast, loading in biphasic state of HPC-PEG solution with even small amount (1 wt%) of MMT leads to the drastic viscosity increase that does not change in further growth of the filler concentration. Elastic properties of the systems under study demonstrate the similar behavior. This effect likely is caused by the interrelationship between deformability of the LC domain structure and the network strength formed by the clay particles. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Mechanical and oxygen barrier properties of organoclay-polyethylene nanocomposite filmsPOLYMER ENGINEERING & SCIENCE, Issue 7 2007Yang Zhong An organically modified montmorillonite was compounded with ethylene vinyl acetate copolymer (EVA), low density polyethylene (LDPE), and high density polyethylene (HDPE) in a twin-screw extruder. The resulting organoclay-polyethylene nanocomposites were then blown into films. Tensile properties and oxygen permeability of these nanocomposite films were investigated to understand the effects of organoclay on different types of polyethylene. It was found that the clay enhancing effects are function of the matrix. The mechanical and oxygen barrier properties of clay/EVA systems increased with clay loading. Both the tensile modulus and oxygen barrier of EVA doubled at 5 wt% clay. Maleic anhydride grafted polyethylene (MAPE) usually is used as a compatibilizer for LDPE and HDPE-based nanocomposites. However, the MAPEs were found to weaken the oxygen barrier of the PEs, especially for HDPE. This is believed to be a result of less compactness caused by the large side groups and the increase in polarity of the MAPEs. Incorporating 5 wt% clay improves the oxygen barrier by 30% and the tensile modulus by 37% for the LDPE/MAPE system. Incorporation of clay does not enhance the properties of the HDPE-based systems, likely due to large domain structure and poor bonding. Halpin,Tsai equation and the tortuous path equation were used to model the tensile modulus and oxygen permeability of the clay/EVA nanocomposite films. POLYM. ENG. SCI., 47:1101,1107, 2007. © 2007 Society of Plastics Engineers [source] The effect of stoichiometry on the fracture toughness of a liquid crystalline epoxyPOLYMER ENGINEERING & SCIENCE, Issue 2 2002Elizabeth J. Robinson The fracture toughness of a liquid crystalline epoxy was compared with that of a standard bisphenol-A based epoxy to understand how both the liquid crystalline structure and the crosslink density affect fracture toughness. For the liquid crystalline epoxy, the liquid crystalline domain size decreased with increasing temperature of cure and away from the stoichiometric formulation. Quantitative fractography showed that there is a competition between the liquid crystalline domain structure and the stoichiometry in determining the fracture toughness. At some cure conditions the effect of the domains is dominant. When the cure conditions are adjusted to reduce the domain size, the domains become too small to affect the fracture toughness, and thus the effect of the stoichiometry is dominant. The result is that the formation of liquid crystalline structure only increases the fracture toughness relative to that of a traditional epoxy at and near the stoichiometric formulation. [source] Structural characterization of unphosphorylated STAT5a oligomerization equilibrium in solution by small-angle X-ray scatteringPROTEIN SCIENCE, Issue 4 2009Pau Bernadó Abstract Signal transducer and activator of transcription (STAT) proteins play a crucial role in the activation of gene transcription in response to extracellular stimuli. The regulation and activity of these proteins require a complex rearrangement of the domains. According to the established models, based on crystallographic data, STATs convert from a basal antiparallel inactive dimer into a parallel active one following phosphorylation. The simultaneous analysis of small-angle X-ray scattering data measured at different concentrations of unphosphorylated human STAT5a core domain unambiguously identifies the simultaneous presence of a monomer and a dimer. The dimer is the minor species but could be structurally characterized by SAXS in the presence of the monomer using appropriate computational tools and shown to correspond to the antiparallel assembly. The equilibrium is governed by a moderate dissociation constant of Kd , 90 ,M. Integration of these results with previous knowledge of the N-terminal domain structure and dissociation constants allows the modeling of the full-length protein. A complex network of intermolecular interactions of low or medium affinity is suggested. These contacts can be eventually formed or broken to trigger the dramatic modifications in the dimeric arrangement needed for STAT regulation and activity. [source] Structure of the B3 domain from Arabidopsis thaliana protein At1g16640PROTEIN SCIENCE, Issue 9 2005Jeanette K. Waltner Abstract A novel DNA binding motif, the B3 domain, has been identified in a number of transcription factors specific to higher plant species, and was recently found to define a new protein fold. Here we report the second structure of a B3 domain, that of the Arabidopsis thaliana protein, At1g16640. As part of an effort to ,rescue' structural genomics targets deemed unsuitable for structure determination as full-length proteins, we applied a combined bioinformatic and experimental strategy to identify an optimal construct containing a predicted conserved domain. By screening a series of N- and C-terminally truncated At1g16640 fragments, we isolated a stable folded domain that met our criteria for structural analysis by NMR spectroscopy. The structure of the B3 domain of At1g16640 consists of a seven-stranded ,-sheet arranged in an open barrel and two short ,-helices, one at each end of the barrel. While At1g16640 is quite distinct from previously characterized B3 domain proteins in terms of amino acid sequence similarity, it adopts the same novel fold that was recently revealed by the RAV1 B3 domain structure. However, putative DNA-binding elements conserved in B3 domains from the RAV, ARF, and ABI3/VP1 subfamilies are largely absent in At1g16640, perhaps suggesting that B3 domains could function in contexts other than transcriptional regulation. [source] Denaturation of replication protein A reveals an alternative conformation with intact domain structure and oligonucleotide binding activityPROTEIN SCIENCE, Issue 5 2004Jonathan E. Nuss Abstract Replication protein A (RPA) is a heterotrimeric, multidomain, single-stranded DNA-binding protein. Using spectroscopic methods and methylene carbene-based chemical modification methods, we have identified conformational intermediates in the denaturation pathway of RPA. Intrinsic protein fluorescence studies reveal unfolding profiles composed of multiple transitions, with midpoints at 1.5, 2.7, 4.2, and 5.3 M urea. CD profiles of RPA unfolding are characterized by a single transition. RPA is stabilized with respect to the CD-monitored transition when bound to a dA15 oligonucleotide. However, oligonucleotide binding appears to exert little, if any, effect on the first fluorescence transition. Methylene carbene chemical modification, coupled with MALDI-TOF mass spectrometry analysis, was also used to monitor unfolding of several specific RPA folds of the protein. The unfolding profiles of the individual structures are characterized by single transitions similar to the CD-monitored transition. Each fold, however, unravels with different individual characteristics, suggesting significant autonomy. Based on results from chemical modification and spectroscopic analyses, we conclude the initial transition observed in fluorescence experiments represents a change in the juxtaposition of binding folds with little unraveling of the domain structures. The second transition represents the unfolding of the majority of fold structure, and the third transition observed by fluorescence correlates with the dissociation of the 70- and 32-kD subunits. [source] BTB and TAZ domain scaffold proteins perform a crucial function in Arabidopsis developmentTHE PLANT JOURNAL, Issue 1 2009Hélčne S. Robert Summary In Arabidopsis, bric-a-brac, tramtrack and broad (BTB) domain scaffold proteins form a family of 80 proteins that have involvement in various signaling pathways. The five members of the subfamily of BTB AND TAZ DOMAIN proteins (BT1,BT5) have a typical domain structure that is only observed in land plants. Here, we present a functional analysis of the BT family, of which at least four members are encoded by auxin-responsive genes. BT1 is a short-lived protein that is characteristically targeted for degradation by the 26S proteasome. Expression pattern, gene structure and sequence analyses indicate that BT1 and BT2 are closely related. They both localize to the nucleus and the cytosol, whereas the remaining BT proteins were determined as cytosolic proteins. Detailed molecular and phenotypic analysis of plants segregating for null mutations in the BT family revealed substantial redundancy among the BT members, and highlighted that BT proteins perform crucial roles in both male and female gametophyte development. BT2 seems to be the predominant gene in this process, in which it is functionally replaced by BT3 and BT1 through reciprocal transcription regulation. Compensational expression alters the steady-state mRNA levels among the remaining BT family members when other BT members are lost, and this contributes towards functional redundancy. Our data provide a surprising example of functional redundancy among genes required during gametophyte development, something that could not be detected in the current screens for gametophyte mutants. [source] (111)p microtwinning in SrRuO3 thin films on (001)p LaAlO3ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009Y. Han SrRuO3 (SRO) thin films grown on (001)p (p = pseudocubic) oriented LaAlO3 (LAO) by pulsed laser deposition have been characterized using transmission electron microscopy. Observations along the ,100,p directions suggests that although the SRO layer maintains a pseudocube-to-pseudocube orientation relationship with the underlying LAO substrate, it has a ferroelastic domain structure associated with a transformation on cooling to room temperature to an orthorhombic Pbnm phase (a,a,c+ Glazer tilt system). In addition, extra diffraction spots located at ±1/6(ooo)p and ±1/3(ooo)p (where `o' indicates an index with an odd number) positions were obtained in ,110,p zone-axis diffraction patterns. These were attributed to the existence of high-density twins on {111}p pseudocubic planes within the SrRuO3 films rather than to more conventional mechanisms for the generation of superstructure reflections. [source] X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinitesACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2001A. Guelylah The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100,300,K. Using DSC measurements, a phase transition has been detected at 213,K. The space group of the low-temperature phase was determined to be P1121 using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P213 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690,(8), b = 20.136,(2), c = 10.0329,(4),Ĺ, , = 90.01,(1)°]. A precise analysis of the BeF4 tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K2Mn2(BeF4)3 and also of a new type of low-temperature structure for langbeinite compounds. [source] Validation of the WHOQOL-BREF among women following childbirthAUSTRALIAN AND NEW ZEALAND JOURNAL OF OBSTETRICS AND GYNAECOLOGY, Issue 2 2010Joan WEBSTER Background:, There is increasing interest in measuring quality of life (QOL) in clinical settings and in clinical trials. None of the commonly used QOL instruments has been validated for use postnatally. Aim:, To assess the psychometric properties of the 26-item WHOQOL-BREF (short version of the World Health Organization Quality of Life assessment) among women following childbirth. Methods:, Using a prospective cohort design, we recruited 320 women within the first few days of childbirth. At six weeks postpartum, participants were asked to complete the WHOQOL-BREF, the Edinburgh Postnatal Depression Index and the Australian Unity Wellbeing Index. Validation of the WHOQOL-BREF included an analysis of internal consistency, discriminate validity, convergent validity and an examination of the domain structure. Results:, In all, 221 (69.1%) women returned their six-week questionnaire. All domains of the WHOQOL-BREF met reliability standards (alpha coefficient exceeding 0.70). The questionnaire discriminated well between known groups (depressed women and non-depressed women. P , 0.000) and demonstrated satisfactory correlations with the Australian Unity Wellbeing index (r , 0.45). The domain structure of the WHOQOL-BREF was also valid in this population of new mothers, with moderate-to-high correlation between individual items and the domain structure to which the items were originally assigned. Conclusion:, The WHOQOL-BRF is a well-accepted and valid instrument in this population and may be used in postnatal clinical settings or for assessing intervention effects in research studies. [source] The structure and domain organization of Escherichia coli isocitrate lyaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2001K. L. Britton Enzymes of the glyoxylate-bypass pathway are potential targets for the control of many human diseases caused by such pathogens as Mycobacteria and Leishmania. Isocitrate lyase catalyses the first committed step in this pathway and the structure of this tetrameric enzyme from Escherichia coli has been determined at 2.1,Ĺ resolution. E. coli isocitrate lyase, like the enzyme from other prokaryotes, is located in the cytoplasm, whereas in plants, protozoa, algae and fungi this enzyme is found localized in glyoxysomes. Comparison of the structure of the prokaryotic isocitrate lyase with that from the eukaryote Aspergillus nidulans reveals a different domain structure following the deletion of approximately 100 residues from the larger eukaryotic enzyme. Despite this, the active sites of the prokaryotic and eukaryotic enzymes are very closely related, including the apparent disorder of two equivalent segments of the protein that are known to be involved in a conformational change as part of the enzyme's catalytic cycle. [source] | ||||||||||||||||||||||||||||||||||