bluuebunny/crossref_metadata_2025 huggingface dataset:
Gephyrin: does splicing affect its function?
Authors: Paarmann I. , Saiyed T. , Schmitt B. , Betz H.
Published: January 2006

Gephyrin is a protein involved in both synaptic anchoring of inhibitory ligand-gated ion channels and molybdenum cofactor synthesis. Substantial progress has been made in understanding its gene and protein structures. Furthermore, numerous binding partners of gephyrin have been identified. The mechanisms by which these interactions occur are unclear at present. Alternative splicing has been proposed to contribute to gephyrin's functional diversity within single cells as well as in different cell types and tissues.
GRIF-1–kinesin-1 interactions: a confocal microscopy study
Authors: Pozo K. , Stephenson F.A.
Published: January 2006

GRIF-1 [GABAA (γ-aminobutyric acidA) receptor interacting factor-1] is a member of a coiled-coil family of proteins thought to function as adaptors in the anterograde trafficking of organelles utilizing the kinesin-1 motor proteins to synapses. To study in more detail the molecular interaction between GRIF-1 and the kinesin-1 family member KIF5C, fluorescent yellow- and fluorescent cyan-tagged GRIF-1, KIF5C, the KIF5C MD (motor domain) and the KIF5C NMD (non-motor domain) fusion proteins were generated. Each was characterized with respect to size and ability to co-associate by immunoprecipitation following expression in HEK-293 (human embryonic kidney 293) cells. Further, their distribution in transfected HEK-293 and transformed African green monkey kidney (COS-7) cells was analysed by confocal microscopy. The fluorescent GRIF-1 and KIF5C fusion proteins were all found to behave as wild-type. Double GRIF-1/KIF5C transfectants revealed co-localization. The GRIF-1/KIF5C and GRIF-1/KIF5C NMD double transfectants showed different subcellular distributions compared with single GRIF-1, KIF5C or KIF5C NMD transfections. These studies confirm the association between GRIF-1 and kinesin-1 NMDs. Fluorescence resonance energy transfer studies are ongoing to characterize this interaction in more detail.
Clathrin and synaptic vesicle endocytosis: studies at the squid giant synapse
Authors: Augustine G.J. , Morgan J.R. , Villalba-Galea C.A. , Jin S. , Prasad K. , Lafer E.M.
Published: January 2006

The role of clathrin-mediated endocytosis in SV (synaptic vesicle) recycling has been studied by combining molecular biology, physiology and electron microscopy at the squid giant synapse. Procedures that prevent clathrin from assembling into membrane coats, such as impairment of binding of the AP180 and AP-2 adaptor proteins, completely prevent membrane budding during endocytosis. These procedures also reduce exocytosis, presumably an indirect effect of a reduction in the number of SVs following block of endocytosis. Disrupting the binding of auxilin to Hsc70 (heat-shock cognate 70) prevents clathrin-coated vesicles from uncoating and also disrupts SV recycling. Taken together, these results indicate that a clathrin-dependent pathway is the primary means of SV recycling at this synapse under physiological conditions.
Polyunsaturated fatty acids and neurotransmission in Caenorhabditis elegans
Authors: Marza E. , Lesa G.M.
Published: January 2006

Changes in PUFA (polyunsaturated fatty acid) metabolism can cause mental retardation and cognitive impairment. However, it is still unclear why altered levels of PUFAs result in neuronal dysfunction. Recent studies on the nematode Caenorhabditis elegans suggest that PUFA depletion may cause cognitive impairment by compromising communication among neurons. Pharmacological and electrophysiological experiments showed that animals devoid of most PUFAs release abnormally low levels of neurotransmitters. In addition, ultrastructural analysis revealed that synapses in these mutants are severely depleted of synaptic vesicles. The conclusion of these studies is that PUFAs are required to maintain a normal pool of synaptic vesicles at pre-synaptic sites, thus ensuring efficient neurotransmission.
Overexpression of tau results in defective synaptic transmission in Drosophila neuromuscular junctions
Authors: Chee F. , Mudher A. , Newman T.A. , Cuttle M. , Lovestone S. , Shepherd D.
Published: January 2006

Synaptic dysfunction is believed to be an early pathological change in neurodegenerative diseases and may cause the earliest clinical symptoms. We have used Drosophila to model a tauopathy in order to analyse the earliest neuronal and synaptic dysfunction. Our work has shown that overexpression of human tau (0N3R) in larval motor neurons causes a disruption of axonal transport and a morphological and functional disruption of NMJs (neuromuscular junctions). Tau-expressing NMJs are smaller with an abnormal structure. Despite abnormal morphology, tau-expressing NMJs retain synaptotagmin expression and can form active zones. Tau-expressing NMJs are functionally abnormal and exhibit disrupted vesicle cycling and synaptic transmission. At low-frequency stimulation (1 Hz), ESPs (evoked synaptic potentials) produced by tau-expressing motor neurons were indistinguishable from wild-type; however, following high-frequency stimulation (50 Hz), ESPs from tau-expressing NMJs were significantly decreased in amplitude. To investigate the mechanism underlying the change in ESPs, we analysed the relative numbers and distribution of mitochondria. This revealed that motor neurons expressing tau had a significant reduction in the number of detectable mitochondria in the pre-synaptic terminal. Our results demonstrate that tau overexpression results in synaptic dysfunction, associated with a reduced complement of functional mitochondria. These findings suggest that disruption of axonal transport and synaptic transmission may be key components of the pathogenic mechanism that underlie neuronal dysfunction in the early stages of tauopathies.
The Escherichia coli cytochrome c maturation (Ccm) apparatus can mature cytochromes with an extra cysteine within or adjacent to the CXXCH motif
Authors: Allen J.W.A. , Ferguson S.J.
Published: January 2006

c-Type cytochromes are characterized by covalent attachment of haem to protein through thioether bonds between the vinyl groups of the haem and the thiols of a Cys-Xaa-Xaa-Cys-His motif. Proteins of this type play crucial roles in the biochemistry of the nitrogen cycle. Many Gram-negative bacteria use the Ccm (cytochrome c maturation) proteins for the post-translational haem attachment to their c-type cytochromes. The Ccm system can correctly mature c-type cytochromes with CCXXCH, CCXCH, CXCCH and CXXCHC motifs, even though these are not found naturally and the extra cysteine might, in principle, disrupt the biogenesis proteins. The non-occurrence of these motifs probably relates to the destructive chemistry that can occur if a free thiol reacts with haem iron to generate a radical.
Specificity of FNR-type regulators in Paracoccus denitrificans
Authors: Veldman R. , Reijnders W.N.M. , van Spanning R.J.M.
Published: January 2006

The three FNR (fumarate and nitrate reductase regulatory protein)-type transcription activators of Paracoccus denitrificans, NarR, NnrR and FnrP, appear to have specific tasks in gene regulation during the switch from aerobic growth to denitrification. We here set out a series of experiments to get a fundamental understanding of the mechanism underlying this specificity. In one of these, we changed the nucleotide sequence of an NnrR box, the binding site for NnrR, into one found in FnrP-regulated promoters. As a result, we observed a change in regulation of that promoter from NnrR to FnrP. In a second series, we constructed hybrid promoters of NnrR-, NarR- and FnrP-regulated promoters and analysed their expression profiles in cells grown under various growth conditions. Our results indicate that the specificity of the FNR-type regulators is determined in part by the quality of the FNR box and in part by the sequences downstream of the FNR box. The latter suggests that specific σ factors are involved in binding any of the Fnr-type regulators in P. denitrificans.
Use of functional genes to quantify denitrifiers in the environment
Authors: Philippot L.
Published: January 2006

During the last decade, application of molecular methods using cultivation-independent approaches has provided new insights into the composition and structure of denitrifying communities in various environments. However, little is known about their abundance, and quantification is still performed using cultivation-based approaches, which are not only biased by the inability to cultivate of many micro-organisms but also fastidious and time-consuming. Two types of cultivation-independent approaches have recently been developed to quantify denitrifiers. The first type, which is based on the hybridization technique, comprises the use of Southern hybridization and DNA arrays. The second type, based on PCR, comprises the use of MPN (most probable number)-PCR, competitive PCR or real-time PCR. In this review, these different approaches will be presented with examples of their application in environmental studies.
Different responses to nitrate and nitrite by the model organism Escherichia coli and the human pathogen Neisseria gonorrhoeae
Authors: Whitehead R.N. , Cole J.A.
Published: January 2006

The ability of Escherichia coli to use both nitrate and nitrite as terminal electron acceptors during anaerobic growth is mediated by the dual-acting two-component regulatory systems NarX-NarL and NarQ-NarP. In contrast, Neisseria gonorrhoeae responds only to nitrite: it expresses only NarQ-NarP. We have shown that although N. gonorrhoeae NarQ can phosphorylate E. coli NarL and NarP, the N. gonorrhoeae NarP is unable to regulate gene expression in E. coli. Mutagenesis experiments have revealed residues in E. coli NarQ that are essential for nitrate and nitrite sensing. Chimaeric proteins revealed domains of NarQ that are important for ligand sensing.
Multiple haem lyase genes indicate substrate specificity in cytochrome c biogenesis
Authors: Hartshorne S. , Richardson D.J. , Simon J.
Published: January 2006

c-Type cytochromes are a widespread class of proteins that play a vital role in the energy-conserving metabolism of prokaryotic and eukaryotic organisms. The key event in cytochrome c biogenesis is the covalent attachment of the haem cofactor to two (or rarely one) cysteine residues arranged in a haem c-binding motif such as CX2–4CH, CXXCK or X3CH. This reaction is catalysed by the membrane-bound enzyme CCHL (cytochrome c haem lyase). Different CCHLs have been described and some of them are dedicated to distinct haem c-binding motifs of cytochromes that are encoded in the vicinity of the respective CCHL gene. Various bacterial genomes contain multiple copies of CCHL-encoding genes, suggesting the presence of non-conventional or even as yet unrecognized haem c-binding motifs. This assumption is exemplified in the present study using the proteobacterium Wolinella succinogenes as a model organism whose genome encodes three CCHL isoenzymes. The discovery of a novel conserved multihaem cytochrome c (MccA) is described.
Approaches to assess the biodiversity of bacteria in natural habitats
Authors: Rösch C. , Eilmus S. , Bothe H.
Published: January 2006

Any attempt to characterize a bacterial community and their functional genes coding for enzymes of the nitrogen cycle is faced with its extreme biodiversity. Novel techniques, based on PCR amplification of target genes in DNA from environmental samples, have been developed for characterizing both cultured and as yet uncultured bacteria in the last few years. Computer-based assignment tools have now been developed utilizing terminal restriction fragments obtained from digestions with multiple restriction enzymes. Such programs allow the gross characterization of bacterial life in any complex bacterial community with confidence.
Mechanism of transcriptional regulation by the Escherichia coli nitric oxide sensor NorR
Authors: Tucker N.P. , D'Autréaux B. , Spiro S. , Dixon R.
Published: January 2006

Nitric oxide (NO) is a highly reactive water-soluble gas encountered by bacteria endogenously as an intermediate of denitrification and exogenously as one of the radical species deployed by macrophages against invading pathogens. Bacteria therefore require a mechanism to detoxify NO. Escherichia coli flavorubredoxin and its associated oxidoreductase, encoded by the norV and norW genes respectively, reduces NO to nitrous oxide under anaerobic conditions. Transcription of the norVW genes is activated in response to NO by the σ54-dependent regulator NorR, a member of the prokaryotic enhancer binding protein family. NorR binds co-operatively to three enhancer sites to regulate transcription of both norVW and the divergently transcribed norR gene. In the present paper, we show that disruption of any one of the three GT-(N7)-AC NorR binding sites in the norR–norVW intergenic region prevents both activation of norVW expression and autogenous repression of the norR promoter by NorR. We have recently demonstrated that the N-terminal GAF (cGMP-specific and -stimulated phosphodiesterases, Anabaena adenylate cyclases and Escherichia coli FhlA) domain of NorR contains a non-haem mononuclear iron centre and senses NO by formation of a mono-nitrosyl iron complex. Site-directed mutagenesis has identified candidate protein ligands to the ferrous iron centre in the GAF domain.
Increased plasma angiotensin II in postural tachycardia syndrome (POTS) is related to reduced blood flow and blood volume
Authors: Stewart Julian M. , Glover June L. , Medow Marvin S.
Published: January 2006

POTS (postural tachycardia syndrome) is associated with low blood volume and reduced renin and aldosterone; however, the role of Ang (angiotensin) II has not been investigated. Previous studies have suggested that a subset of POTS patients with increased vasoconstriction related to decreased bioavailable NO (nitric oxide) have decreased blood volume. Ang II reduces bioavailable NO and is integral to the renin–Ang system. Thus, in the present study, we investigated the relationship between blood volume, Ang II, renin, aldosterone and peripheral blood flow in POTS patients. POTS was diagnosed by 70° upright tilt, and supine calf blood flow, measured by venous occlusion plethysmography, was used to subgroup POTS patients. A total of 23 POTS patients were partitioned; ten with low blood flow, eight with normal flow and five with high flow. There were ten healthy volunteers. Blood volume was measured by dye dilution. All biochemical measurements were performed whilst supine. Blood volume was decreased in low-flow POTS (2.14±0.12 litres/m2) compared with controls (2.76±0.20 litres/m2), but not in the other subgroups. PRA (plasma renin activity) was decreased in low-flow POTS compared with controls (0.49±0.12 compared with 0.90±0.18 ng of Ang I·ml−1·h−1 respectively), whereas plasma Ang II was increased (89±20 compared with 32±4 ng/l), but not in the other subgroups. PRA correlated with aldosterone (r=+0.71) in all subjects. PRA correlated negatively with blood volume (r=−0.72) in normal- and high-flow POTS, but positively (r=+0.65) in low-flow POTS. PRA correlated positively with Ang II (r=+0.76) in normal- and high-flow POTS, but negatively (r=−0.83) in low-flow POTS. Blood volume was negatively correlated with Ang II (r=−0.66) in normal- and high-flow POTS and in five low-flow POTS patients. The remaining five low-flow POTS patients had reduced blood volume and increased Ang II which was not correlated with blood volume. The data suggest that plasma Ang II is increased in low-flow POTS patients with hypovolaemia, which may contribute to local blood flow dysregulation and reduced NO bioavailability.
How does endothelin induce vascular oxidative stress in mineralocorticoid hypertension?
Authors: Pollock David M.
Published: January 2006

Endothelin and reactive oxygen species have been identified as important mediators in the pathogenesis of hypertension and associated end-organ damage. In the present issue of Clinical Science, Callera and co-workers have provided new evidence that endothelin stimulates mitochondria to generate reactive oxygen species in the vascular wall during mineralocorticoid-induced hypertension in the rat. These studies open a new line of investigation that could be important for the development of therapeutic strategies; however, there still remains a great deal of uncertainty about the mechanisms that define the relationship between endothelin and oxidative stress in hypertension.
Nonadditivity in van der Waals interactions within multilayers
Authors: Podgornik R. , French R. H. , Parsegian V. A.
Published: January 2006

Working at the macroscopic continuum level, we investigate effective van der Waals interactions between two layers within a multilayer assembly. By comparing the pair interactions between two layers with effective pair interactions within an assembly we assess the significant consequences of nonadditivity of van der Waals interactions. This allows us to evaluate the best numerical estimate to date for the Hamaker coefficient of van der Waals interactions in lipid-water multilamellar systems.
Efficient step size selection for the tau-leaping simulation method
Authors: Cao Yang , Gillespie Daniel T. , Petzold Linda R.
Published: January 2006

The tau-leaping method of simulating the stochastic time evolution of a well-stirred chemically reacting system uses a Poisson approximation to take time steps that leap over many reaction events. Theory implies that tau leaping should be accurate so long as no propensity function changes its value “significantly” during any time step τ. Presented here is an improved procedure for estimating the largest value for τ that is consistent with this condition. This new τ-selection procedure is more accurate, easier to code, and faster to execute than the currently used procedure. The speedup in execution will be especially pronounced in systems that have many reaction channels.
Single-domain electromechanical constants for Pb(Zn1∕3Nb2∕3)O3–4.5%PbTiO3 from micro-Brillouin scattering
Authors: Ahart Muhtar , Asthagiri Aravind , Dera Przemyslaw , Mao Ho-kwang , Cohen R. E. , Hemley Russell J.
Published: January 2006

We report a complete set of elastic and piezoelectric constants for single-domain rhombohedral Pb(Zn1∕3Nb2∕3)O3–4.5%PbTiO3, poled in the ⟨111⟩ direction using micro-Brillouin scattering. We find the bulk modulus and elastic constants to agree with the values obtained from ultrasonic and resonance methods, but obtain smaller piezoelectric constants. Brillouin spectroscopy probes microregions of the crystal at high frequencies. The differences in material constants obtained by acoustic measurements on multidomain samples and Brillouin measurements of single domains are due to frequency dependence of the piezoelectric constants, and/or point to extrinsic contributions of domain boundaries to the electromechanical response in single-crystal relaxor ferroelectrics.
Early stage of implosion in inertial confinement fusion: Shock timing and perturbation evolution
Authors: Goncharov V. N. , Gotchev O. V. , Vianello E. , Boehly T. R. , Knauer J. P. , McKenty P. W. , Radha P. B. , Regan S. P. , Sangster T. C. , Skupsky S. , Smalyuk V. A. , Betti R. , McCrory R. L. , Meyerhofer D. D. , Cherfils-Clérouin C.
Published: January 2006

Excessive increase in the shell entropy and degradation from spherical symmetry in inertial confinement fusion implosions limit shell compression and could impede ignition. The entropy is controlled by accurately timing shock waves launched into the shell at an early stage of an implosion. The seeding of the Rayleigh-Taylor instability, the main source of the asymmetry growth, is also set at early times during the shock transit across the shell. In this paper we model the shock timing and early perturbation growth of directly driven targets measured on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. By analyzing the distortion evolution, it is shown that one of the main parameters characterizing the growth is the size of the conduction zone Dc, defined as a distance between the ablation front and the laser deposition region. Modes with kDc>1 are stable and experience oscillatory behavior [V. N. Goncharov, Phys. Rev. Lett. 82, 2091 (1999)]. The model shows that the main stabilizing mechanism is the dynamic overpressure due to modulations in the blow-off velocity inside the conduction zone. The long wavelengths with kDc<1 experience growth because of coupled Richtmyer-Meshkov-like and Landau-Darrieus instabilities [L. D. Landau and E. M. Lifshitz, Fluid Mechanics (Pergamon, New York, 1982)]. To match the simulation results with both the shock timing and perturbation growth measurements a new nonlocal thermal transport model is developed and used in hydrocodes.
A small and stable covalently bound trianion
Authors: Feuerbacher Sven , Cederbaum Lorenz S.
Published: January 2006

Stable doubly charged anions have become well known over the past decade, but the knowledge about higher-charged molecules is still sparse. Especially the minimum size of a covalently bound trianion which is still stable is an open question. Here, we present the smallest trianion of this kind known up to now, namely, B(C2CO2)33−. After establishing its geometrical parameters, we investigate its stability with respect to electron autodetachment and fragmentation of the molecular framework. Our results lend strong support to the notion that this trianion indeed represents a stable compound which should be observable in the gas phase.
Single attosecond pulse generation by nonlinear Thomson scattering in a tightly focused intense laser beam
Authors: Lan Pengfei , Lu Peixiang , Cao Wei
Published: January 2006

The relativistic nonlinear Thomson scattering of a tightly focused intense laser pulse by an electron is investigated, and the temporal and spectral characters of the radiation are discussed. In a tightly focused laser pulse with an intensity of approximately 1020W∕cm2 and a pulse duration of 20fs, the electron is scattered away from the focus quickly by the ponderomotive force and therefore the radiation emitted at the focus is much higher than that at other regions. As a result, a single ultrashort pulse of 3.8 as is generated and its corresponding spectrum is broadened to 200 orders of the frequency of the driving laser. With increasing the laser intensity, the signal-to-noise of the radiated pulse increases, and the pulse duration decreases. Moreover, the phase behavior of the spectral components and the dependence of the radiated power on the laser intensity are discussed.
The process of electron acceleration during collisionless magnetic reconnection
Authors: Fu X. R. , Lu Q. M. , Wang S.
Published: January 2006

Two-dimensional particle-in-cell simulations are performed to study electron acceleration in collisionless magnetic reconnection. The process of electron acceleration is investigated by tracing typical electron trajectories. When there is no initial guide field, the electrons can be accelerated in both the X-type and O-type regions. In the X-type region, the electrons can be reflected back and enter the acceleration region several times before they leave the diffusion region. In this way, the electrons can be accelerated by the inductive electric field to high energy. In the O-type region, the trapped electrons can be accelerated when they are trapped in the magnetic island. When there is an initial guide field, the electrons can only be accelerated in the X-type region, and no obvious acceleration is observed in the O-type region. In the X-type region, the electrons are not demagnetized and they gyrate with the force of the guide field. Although no electron reflection is observed in this region, the acceleration efficiency can be enhanced through staying longer time in the diffusion region due to their gyration motion.
Atomic-resolution observations of semicrystalline intergranular thin films in silicon nitride
Authors: Ziegler A. , Idrobo J. C. , Cinibulk M. K. , Kisielowski C. , Browning N. D. , Ritchie R. O.
Published: January 2006

Nanoscale intergranular films in doped silicon-nitride ceramics are known to markedly affect toughness and creep resistance. They are regarded as being fully amorphous, but are shown here to have a semicrystalline structure in a Ce-doped Si3N4. Using two different but complementary high-resolution electron-microscopy methods, the intergranular atomic structure, imaged with sub-angstrom resolution, reveals that segregated cerium ions take very periodic positions, along the intergranular-phase∕matrix-grain interface and as a semicrystalline structure spanning the width of the intergranular phase. This result has broad implications for the understanding of the structure and role of the intergranular phase in enhancing the mechanical properties of ceramics.
Long-lived, coherent acoustic phonon oscillations in GaN single crystals
Authors: Wu S. , Geiser P. , Jun J. , Karpinski J. , Park J.-R. , Sobolewski Roman
Published: January 2006

We report on coherent acoustic phonon (CAP) oscillations studied in high-quality bulk GaN single crystals with a two-color femtosecond optical pump-probe technique. Using a far-above-the-band gap ultraviolet excitation (∼270nm wavelength) and a near-infrared probe beam (∼810nm wavelength), the long-lived, CAP transients were observed within a 10 ns time-delay window between the pump and probe pulses, with a dispersionless (proportional to the probe-beam wave vector) frequency of ∼45GHz. The measured CAP attenuation corresponded directly to the absorption of the probe light in bulk GaN, indicating that the actual (intrinsic) phonon-wave attenuation in our crystals was significantly smaller than the measured 65.8cm−1 value. The velocity of the phonon propagation was equal to the velocity of sound in GaN.
Interaction of HfO2∕SiO2∕Si structures with deuterium gas
Authors: Driemeier C. , Miotti L. , Baumvol I. J. R. , Radtke C. , Gusev E. P. , Kim M. J. , Wallace R. M.
Published: January 2006

Hf O 2 films (2.5 to 12 nm) deposited on thermal SiO2 (1.5 nm) on Si were annealed in deuterium gas at 400–600 °C and incorporated D amounts were quantified using the D(He3,p)He4 nuclear reaction. We found ∼1013Dcm−2 in the SiO2 interlayer region and up to 2.2×1014Dcm−2 near the HfO2 surface, whereas D amounts in the bulk of the HfO2 films were determined to be below 1013cm−2. However, analyses employing the H1(N15,αγ)C12 nuclear resonant reaction showed much more spurious H present in the bulk of HfO2 films. Mechanisms of D incorporation and desorption as well as contribution of the present results to the understanding of HfO2-based devices are discussed.
Resonant Raman scattering from CdS nanowires
Authors: Abdi A. , Titova L. V. , Smith L. M. , Jackson H. E. , Yarrison-Rice J. M. , Lensch J. L. , Lauhon L. J.
Published: January 2006

Resonant Raman scattering (RRS) was used to probe the electronic states of CdS nanowires (∼10nm diameter) grown by chemical vapor deposition. Individual Ar+ laser lines were used to vary the excitation energy while observing scattering from CdS phonons; strong 1-longitudinal optical (LO) and 2-LO Raman resonances were readily observed within the broader photoluminescence emission. The energy separation between the peaks of the 1-LO and 2-LO resonance was found to be 34 meV, in good agreement with bulk values. These results demonstrate that RRS is a powerful tool for probing the electronic and vibrational properties of semiconductor nanowires.
Hexagonal Ba(Ti1−xMnx)O3 ceramics: Microstructural evolution and microwave dielectric properties
Authors: Wang Sea-Fue , Hsu Ya-Chi , Chu Jinn P. , Wu Cheng-Hui
Published: January 2006

Up to date, little work has been done to explore the possible application of the high-temperature 6H-hexagonal BaTiO3 polymorph (h-BaTiO3). In this letter, the feasibility for use of h-BaTiO3 ceramics as microwave dielectric resonators was evaluated through the Mn substitution in B sites. Based on the overall performance, the best results were acquired for the h-Ba(Ti0.65Mn0.35)O3 (εr:41.2, Q∙fr:14300, and τf:18.6ppm∕°C) and h-Ba(Ti0.50Mn0.50)O3 ceramics (εr:32.8, Q∙fr:6,450, and τf:3.6ppm∕°C). These results suggest the hexagonal Ba(Ti1−xMnx)O3 ceramics are suited for the dielectric resonator applications.
Ultrasonic anomalies in La1∕3Sr2∕3MO3 (M=Fe, Mn)
Authors: Kong Hui , Zhu Changfei
Published: January 2006

The longitudinal ultrasonic velocity (Vl), magnetization, specific heat, and resistivity of polycrystalline La1∕3Sr2∕3FeO3 have been measured between 20 and 300 K. The material undergoes charge-ordering (CO) transition at about 200 K accompanied by an antiferromagnetic ordering. Upon cooling down from 300 K, a substantial softening in Vl above the charge-ordering transition temperature TCO and dramatic stiffening below TCO are observed. This feature is similar in character to that of charge-ordered La1∕3Sr2∕3MnO3, and gives clear evidence for electron-phonon coupling in La1∕3Sr2∕3FeO3. Below 181 K, another unexpected softening in Vl is observed, which is attributed to the breathing-type distortion of an Fe-O octahedron.
High performance optically pumped antimonide lasers operating in the 2.4–9.3μm wavelength range
Authors: Kaspi R. , Ongstad A. P. , Dente G. C. , Chavez J. R. , Tilton M. L. , Gianardi D. M.
Published: January 2006

We provide an update on the further development of optically pumped semiconductor lasers based on the InAs∕InGaSb∕InAs type-II quantum wells. We show increased power generation, as well as the inherent flexibility to produce devices that can emit at any wavelength in the ∼2.4μm to ∼9.3μm range with consistently high photon-to-photon conversion rates.
Short‐term longitudinal study of a child with Williams syndrome
Authors: Stojanovik Vesna , James Deborah
Published: January 2006

Background: The superiority of language and communication skills in children and adults with Williams syndrome (WS) is currently being debated. Whilst there have been a number of reports of precursors of language in WS in children who have already developed language, there have not been many studies that have prospectively investigated precursors of language in pre‐verbal children with WS.

Aims: To investigate the development of early social communication skills before the onset of language in WS.

Methods & Procedures: A short‐term longitudinal single case study was carried out spanning 10 months. The child was assessed five times using parent report, observation of mother—child interactions and by administering the Pre‐verbal Communication Schedule, the Pragmatics Profile of Early Communication Skills and the Pre‐School Language Scale − 3.

Outcomes & Results: Longitudinal comparisons showed that the level of verbal communication in the child with WS always lagged behind the level of motor and cognitive development.

Conclusions: The results indicate that rather than being a strength, social communication was an area of weakness relative to other aspects of development in this case. This case raises the potential desirability for early speech and language assessment and intervention in infants with WS.
Distinct Roles for the Essential MYST Family HAT Esa1p in Transcriptional Silencing
Authors: Clarke Astrid S. , Samal Eva , Pillus Lorraine
Published: January 2006

Among acetyltransferases, the MYST family enzyme Esa1p is distinguished for its essential function and contribution to transcriptional activation and DNA double-stranded break repair. Here we report that Esa1p also plays a key role in silencing RNA polymerase II (Pol II)-transcribed genes at telomeres and within the ribosomal DNA (rDNA) of the nucleolus. These effects are mediated through Esa1p's HAT activity and correlate with changes within the nucleolus. Esa1p is enriched within the rDNA, as is the NAD-dependent protein deacetylase Sir2p, and the acetylation levels of key Esa1p histone targets are reduced in the rDNA in esa1 mutants. Although mutants of both ESA1 and SIR2 have enhanced rates of rDNA recombination, esa1 effects are more modest yet result in distinct structural changes of rDNA chromatin. Surprisingly, increased expression of ESA1 can bypass the requirement for Sir2p in rDNA silencing, suggesting that these two enzymes with seemingly opposing activities both contribute to achieve optimal nucleolar chromatin structure and function.
Senescence of Human Fibroblasts after Psoralen Photoactivation Is Mediated by ATR Kinase and Persistent DNA Damage Foci at Telomeres
Authors: Hovest Miriam Grosse , Brüggenolte Nicole , Hosseini Kijawasch Shah , Krieg Thomas , Herrmann Gernot
Published: January 2006

Cellular senescence is a phenotype that is likely linked with aging. Recent concepts view different forms of senescence as permanently maintained DNA damage responses partially characterized by the presence of senescence-associated DNA damage foci at dysfunctional telomeres. Irradiation of primary human dermal fibroblasts with the photosensitizer 8-methoxypsoralen and ultraviolet A radiation (PUVA) induces senescence. In the present study, we demonstrate that senescence after PUVA depends on DNA interstrand cross-link (ICL) formation that activates ATR kinase. ATR is necessary for the manifestation and maintenance of the senescent phenotype, because depletion of ATR expression before PUVA prevents induction of senescence, and reduction of ATR expression in PUVA-senesced fibroblasts releases cells from growth arrest. We find an ATR-dependent phosphorylation of the histone H2AX (γ-H2AX). After PUVA, ATR and γ-H2AX colocalize in multiple nuclear foci. After several days, only few predominantly telomere-localized foci persist and telomeric DNA can be coimmunoprecipitated with ATR from PUVA-senesced fibroblasts. We thus identify ATR as a novel mediator of telomere-dependent senescence in response to ICL induced by photoactivated psoralens.
Uncoupling the Central Spindle-associated Function of the Chromosomal Passenger Complex from Its Role at Centromeres
Authors: Lens Susanne M.A. , Rodriguez Jose A. , Vader Gerben , Span Simone W. , Giaccone Giuseppe , Medema René H.
Published: January 2006

Survivin is a component of the chromosomal passenger complex (CPC) that plays a role in maintenance of an active spindle checkpoint and in cytokinesis. To study whether these different functions can be attributed to distinct domains within the Survivin protein, we complemented Survivin-depleted cells with a variety of point- and deletion-mutants of Survivin. We show that an intact baculovirus IAP repeat (BIR) domain is required for proper spindle checkpoint functioning, but dispensable for cytokinesis. In line with this, mutants lacking an intact BIR domain localized normally to the central spindle, but their localization to inner centromeres was severely perturbed. Consequently, these mutants failed to recruit Aurora B, Borealin/Dasra B, and BubR1 to centromeres and kinetochores, but they had retained the ability to recruit Aurora B and Borealin/Dasra B to the midzone and midbody. Thus, the C terminus of Survivin is sufficient for central spindle localization and execution of cytokinesis, but the additional presence of a functional BIR domain is essential for centromere targeting and spindle checkpoint function. Importantly, our data show that the function of the CPC at the centromere can be separated from its function at the central spindle and that execution of cytokinesis does not require prior concentration of the CPC at centromeres.
Phosphorylation ofXenopusRad1 and Hus1 Defines a Readout for ATR Activation That Is Independent of Claspin and the Rad9 Carboxy Terminus
Authors: Lupardus Patrick J. , Cimprich Karlene A.
Published: January 2006

The DNA damage checkpoint pathways sense and respond to DNA damage to ensure genomic stability. The ATR kinase is a central regulator of one such pathway and phosphorylates a number of proteins that have roles in cell cycle progression and DNA repair. Using the Xenopus egg extract system, we have investigated regulation of the Rad1/Hus1/Rad9 complex. We show here that phosphorylation of Rad1 and Hus1 occurs in an ATR- and TopBP1-dependent manner on T5 of Rad1 and S219 and T223 of Hus1. Mutation of these sites has no effect on the phosphorylation of Chk1 by ATR. Interestingly, phosphorylation of Rad1 is independent of Claspin and the Rad9 carboxy terminus, both of which are required for Chk1 phosphorylation. These data suggest that an active ATR signaling complex exists in the absence of the carboxy terminus of Rad9 and that this carboxy-terminal domain may be a specific requirement for Chk1 phosphorylation and not necessary for all ATR-mediated signaling events. Thus, Rad1 phosphorylation provides an alternate and early readout for the study of ATR activation.
Synergistic effects of plant‐growth promoting rhizobacteria andRhizobiumon nodulation and nitrogen fixation by pigeonpea (Cajanus cajan)
Authors: Tilak K. V. B. R. , Ranganayaki N. , Manoharachari C.
Published: January 2006

Plant‐growth promoting rhizobacteria (PGPR), in conjuction with efficientRhizobium, can affect the growth and nitrogen fixation in pigeonpea by inducing the occupancy of introducedRhizobiumin the nodules of the legume. This study assessed the effect of different plant‐growth promoting rhizobacteria (Azotobacter chroococcum,Azospirillum brasilense,Pseudomonas fluorescens,Pseudomonas putidaandBacillus cereus) on pigeonpea (Cajanus cajan(L) Milsp.) cv. P‐921 inoculated withRhizobiumsp. (AR‐2–2 k). A glasshouse experiment was carried out with a sandy‐loam soil in which the seeds were treated withRhizobiumalone or in combination with several PGPR isolates. It was monitored on the basis of nodulation, N2fixation, shoot biomass, total N content in shoot and legume grain yield. The competitive ability of the introducedRhizobiumstrain was assessed by calculating nodule occupancy. The PGPR isolates used did not antagonize the introducedRhizobiumstrain and the dual inoculation with eitherPseudomonas putida,P. fluorescensorBacillus cereusresulted in a significant increase in plant growth, nodulation and enzyme activity overRhizobium‐inoculated and uninoculated control plants. The nodule occupancy of the introducedRhizobiumstrain increased from 50% (withRhizobiumalone) to 85% in the presence ofPseudomonas putida. This study enabled us to select an ideal combination of efficientRhizobiumstrain and PGPR for pigeonpea grown in the semiarid tropics.
Root, rhizosphere and root‐free respiration in soils under grassland and forest plants
Authors: Chen C. R. , Condron L. M. , Xu Z. H. , Davis M. R. , Sherlock R. R
Published: January 2006

Plants significantly affect rates of carbon (C) turnover in soils, both because they are sources of carbon through exudation in the rhizosphere and litter‐fall, and because rhizosphere microbes stimulated by roots also metabolize native soil carbon. Different plant species affect these components of soil carbon turnover in different ways, but the quantitative information on this is lacking for different ecosystems and soil‐plant combinations. To compare the effects of grassland and forest plant species on the components of rhizosphere respiration in different soils, we grew ryegrass (Lolium perenne) and radiata pine (Pinus radiata D. Don) in two silt loam soils in pots in a glasshouse, and in seven samplings over 45 weeks measured total (Rtotal), root (Rroot) and root‐free soil respiration (Rrfs), the latter from respiration in unplanted controls. We calculated rhizosphere respiration (Rrhizo), defined here as the net of that fuelled by native soil C and root‐derived C, from Rtotal less Rroot+Rrfs. We also measured plant growth and total, water‐soluble and microbial biomass C in the soils at each sampling. Results showed that Rrfs decreased over the experimental period in both soils. Under ryegrass, Rroot, Rrhizo and Rtotal increased up to 14 weeks after planting and then stabilized, whereas under radiata pine, they continued to increase throughout the experiment. By the end of the experiment, the Rroot, Rrhizo and Rrfs components accounted for 49–58, 31–50 and 1–11% of soil total respiration under ryegrass, respectively, and 43–66, 29–53 and 1–5% under radiata pine. The greater Rroot, Rrhizo and Rtotal values under radiata pine were related to greater root biomass and root‐derived organic C, and enhanced microbial mineralization of native soil organic C.
Modelling the rhizosphere: a review of methods for ‘upscaling’ to the whole‐plant scale
Authors: Darrah P. R. , Jones D. L. , Kirk G. J. D. , Roose T.
Published: January 2006

The rhizosphere is a dynamic region where multiple interacting processes in the roots and surrounding soil take place, with dimensions set by the distance to which the zone of root influence spreads into the soil. Its complexity is such that some form of mathematical modelling is essential for understanding which of the various processes operating are important, and a minimal model of the rhizosphere must provide information on (a) the spatiotemporal concentration changes of mobile solutes in the root‐influenced soil, and (b) the cumulative uptake of solutes per unit length of root over time. Both are unique for a given set of parameters and initial conditions and hence the model is fully deterministic. ‘Up‐scaling’ to uptake by whole plants by integrating individual fluxes requires a measure of the growth and senescence of the root system. Root architecture models are increasingly successful in providing this. The spatio‐temporal scales of the rhizosphere and roots are sufficiently different that they can be treated separately, and this greatly simplifies modelling. The minimal model has been successfully applied to the more‐mobile nutrients in soil, such as nitrate or potassium, but much less successfully to less‐soluble nutrients such as phosphorus, because other, undescribed processes become important. These include transfers from unavailable forms, heterogeneity of resource distribution, root competition, water redistribution and adaptive processes. Incorporating such processes into models can disrupt independent scaling. In general, scaling from the scale of the individual root to that of the whole plant does not pose insuperable problems. Paradoxically, the major challenge in introducing more complexity is that experimental corroboration of the model is required at the individual root scale.
Global tectonics under g having a minute westward tilt
Authors: Bostrom Robert C.
Published: January 2006

The convection seen to affect Moon's mantle takes place under gravity having a component of asymmetry, in the form of a minute westward slope or tilt constituting the external part of the field. Its effect is explored employing the equivalent potential, denominated . Its nature is to bias convection of internal origin, inducing east–west polarization of a type prominent in global tectonics. Separately, research at Harvard has shown that by causing advection of non‐hydrostatic masses within the heterogeneous mantle, deep‐seated convection inevitably displaces the axis of maximum moment, compelling polar wander. A reconstruction based on observed dissipation suggests that the combined effect of these factors is to contribute a not inconsiderable low‐latitude, surface‐west component to the structure of the convection. Cumulative alteration in the direction ‘west’ must eventually require global rearrangement of its cell structure, offering explanation of the abrupt Mesozoic–Tertiary transition and progressive net lithosphere rotation.
Methods and concepts in quantifying resistance to drought, salt and freezing, abiotic stresses that affect plant water status
Authors: Verslues Paul E. , Agarwal Manu , Katiyar‐Agarwal Surekha , Zhu Jianhua , Zhu Jian‐Kang
Published: January 2006

The abiotic stresses of drought, salinity and freezing are linked by the fact that they all decrease the availability of water to plant cells. This decreased availability of water is quantified as a decrease in water potential. Plants resist low water potential and related stresses by modifying water uptake and loss to avoid low water potential, accumulating solutes and modifying the properties of cell walls to avoid the dehydration induced by low water potential and using protective proteins and mechanisms to tolerate reduced water content by preventing or repairing cell damage. Salt stress also alters plant ion homeostasis, and under many conditions this may be the predominant factor affecting plant performance. Our emphasis is on experiments that quantify resistance to realistic and reproducible low water potential (drought), salt and freezing stresses while being suitable for genetic studies where a large number of lines must be analyzed. Detailed protocols for the use of polyethylene glycol‐infused agar plates to impose low water potential stress, assay of salt tolerance based on root elongation, quantification of freezing tolerance and the use of electrolyte leakage experiments to quantify cellular damage induced by freezing and low water potential are also presented.
Practical approaches to plant volatile analysis
Authors: Tholl Dorothea , Boland Wilhelm , Hansel Armin , Loreto Francesco , Röse Ursula S.R. , Schnitzler Jörg‐Peter
Published: January 2006

Plants emit volatile organic compounds (VOCs) that play important roles in their interaction with the environment and have a major impact on atmospheric chemistry. The development of static and dynamic techniques for headspace collection of volatiles in combination with gas chromatography–mass spectrometry analysis has significantly improved our understanding of the biosynthesis and ecology of plant VOCs. Advances in automated analysis of VOCs have allowed the monitoring of fast changes in VOC emissions and facilitated in vivo studies of VOC biosynthesis. This review presents an overview of methods for the analysis of plant VOCs, including their advantages and disadvantages, with a focus on the latest technical developments. It provides guidance on how to select appropriate instrumentation and protocols for biochemical, physiological and ecologically relevant applications. These include headspace analyses of plant VOCs emitted by the whole organism, organs or enzymes as well as advanced on‐line analysis methods for simultaneous measurements of VOC emissions with other physiological parameters.
Measuring multiple fluxes through plant metabolic networks
Authors: Ratcliffe R.G. , Shachar‐Hill Y.
Published: January 2006

Fluxes through metabolic networks are crucial for cell function, and a knowledge of these fluxes is essential for understanding and manipulating metabolic phenotypes. Labeling provides the key to flux measurement, and in network flux analysis the measurement of multiple fluxes allows a flux map to be superimposed on the metabolic network. The principles and practice of two complementary methods, dynamic and steady‐state labeling, are described, emphasizing best practice and illustrating their contribution to network flux analysis with examples taken from the plant and microbial literature. The principal analytical methods for the detection of stable isotopes are also described, as well as the procedures for obtaining flux maps from labeling data. A series of boxes summarizing the key concepts of network flux analysis is provided for convenience.