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TonB-dependent outer-membrane proteins and siderophore utilization in Pseudomonas fluorescens Pf-5

HARTNEY, Sierra L.; MAZURIER, Sylvie; KIDARSA, Teresa A.; QUECINE, Maria Carolina; LEMANCEAU, Philippe; LOPER, Joyce E.
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
ENG
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The soil bacterium Pseudomonas fluorescens Pf-5 produces two siderophores, a pyoverdine and enantio-pyochelin, and its proteome includes 45 TonB-dependent outer-membrane proteins, which commonly function in uptake of siderophores and other substrates from the environment. The 45 proteins share the conserved beta-barrel and plug domains of TonB-dependent proteins but only 18 of them have an N-terminal signaling domain characteristic of TonB-dependent transducers (TBDTs), which participate in cell-surface signaling systems. Phylogenetic analyses of the 18 TBDTs and 27 TonB-dependent receptors (TBDRs), which lack the N-terminal signaling domain, suggest a complex evolutionary history including horizontal transfer among different microbial lineages. Putative functions were assigned to certain TBDRs and TBDTs in clades including well-characterized orthologs from other Pseudomonas spp. A mutant of Pf-5 with deletions in pyoverdine and enantio-pyochelin biosynthesis genes was constructed and characterized for iron-limited growth and utilization of a spectrum of siderophores. The mutant could utilize as iron sources a large number of pyoverdines with diverse structures as well as ferric citrate, heme, and the siderophores ferrichrome, ferrioxamine B...

Chronic ouabain treatment increases the contribution of nitric oxide to endothelium-dependent relaxation

ARAS-LOPEZ, R.; BLANCO-RIVERO, J.; HERNANZ, R.; BRIONES, A. M.; ROSSONI, L. V.; FERRER, M.; SALAICES, M.; BALFAGON, G.
Fonte: SERVICIO PUBLICACIONES UNIVERSIDAD NAVARRA Publicador: SERVICIO PUBLICACIONES UNIVERSIDAD NAVARRA
Tipo: Artigo de Revista Científica
ENG
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The aim of this study was to analyze the contribution of nitric oxide, prostacyclin and endothelium-dependent hyperpolarizing factor to endothelium-dependent vasodilation induced by acetylcholine in rat aorta from control and ouabain-induced hypertensive rats. Preincubation with the nitric oxide synthase inhibitor N-omega-nitro-L-arginine methyl esther (L-NAME) inhibited the vasodilator response to acetylcholine in segments from both groups but to a greater extent in segments from ouabain-treated rats. Basal and acetylcholine-induced nitric oxide release were higher in segments from ouabain-treated rats. Preincubation with the prostacyclin synthesis Inhibitor tranylcypromine or with the cyclooxygenase inhibitor indomethacin inhibited the vasodilator response to acetylcholine in aortic segments front both groups. The Ca(2+)-dependent potassium channel blocker charybdotoxin inhibited the vasodilator response to acetylcholine only In segments from control rats. These results indicate that hypertension induced by chronic ouabain treatment is accompanied by increased endothelial nitric oxide participation and impaired endothelium-dependent hyperpolarizing factor contribution In acetylcholine-induced relaxation. These effects might explain the lack of effect of ouabain treatment oil acetylcholine responses in rat aorta.; Instituto de Salud Carlos III; Instituto de Salud Carlos III[PI051767]; Instituto de Salud Carlos III[RD06/0014/0011]; Instituto de Salud Carlos III; Ministerio de Educacion y Ciencia[SAF2006-02376]; Ministerio de Educacion y Ciencia; Ministerio de Educacion y Ciencia[SAF2006-07888]; Ministerio de Educacion y Ciencia; Fundacion Medica Mutua Madrilena; Fundacion Medica Mutua Madrilena[MMA-06]; Branco de Santander Central Hispano; Branco de Santander Central Hispano

Analysis of the Caulobacter crescentus Zur regulon reveals novel insights in zinc acquisition by TonB-dependent outer membrane proteins

Mazzon, Ricardo Ruiz; Braz, Vânia Santos; Silva Neto, José Freire da; Marques, Marilis do Valle
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
EN
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Abstract Background Intracellular zinc concentration needs to be maintained within strict limits due to its toxicity at high levels, and this is achieved by a finely regulated balance between uptake and efflux. Many bacteria use the Zinc Uptake Regulator Zur to orchestrate zinc homeostasis, but little is known regarding the transport of this metal across the bacterial outer membrane. Results In this work we determined the Caulobacter crescentus Zur regulon by global transcriptional and in silico analyses. Among the genes directly repressed by Zur in response to zinc availability are those encoding a putative high affinity ABC uptake system (znuGHI), three TonB-dependent receptors (znuK, znuL and znuM) and one new putative transporter of a family not yet characterized (zrpW). Zur is also directly involved in the activation of a RND and a P-type ATPase efflux systems, as revealed by β-galactosidase and site-directed mutagenesis assays. Several genes belonging to the Fur regulon were also downregulated in the zur mutant, suggesting a putative cross-talk between Zur and Fur regulatory networks. Interestingly, a phenotypic analysis of the znuK and znuL mutants has shown that these genes are essential for growth under zinc starvation...

Shot Noise dependente de spin em sistemas com tunelamento: modelo semiclássico; Spin-dependent shot noise in systems with scattering: semiclassical model

Brito, Fernando Graciano de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 13/04/2000 PT
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Neste trabalho investigamos pela primeira vez flutuações dependentes de spin em correntes eletrônicas polarizadas através de estruturas magnéticas. Nosso sistema físico consiste de uma heteroestrutura com tunelamento ressonante formada por um poço ou "ponto" quântico contendo Mn, confinado entre duas barreiras de potencial. Usamos um modelo semiclássico baseado em equações de taxa para calcular as ocupações dos estados ressonantes up e down. Estas equações são derivadas de uma equação mestra que descreve a probabilidade de ocupação dos estados de spin em um dado tempo. Funções correlação corrente-corrente são expressas em termos das funções correlação hop-hop (associadas à transições entre os níveis ressonantes up e down) e o shot noise dependente de spin é determinado em termos da matriz variância do sistema, também derivada da equação mestra. Quando consideramos um feixe polarizado e tempos distintos (τ ↑ ↓ ≠ τ ↓ ↑), podemos obter ambas "correlações positivas" (‹ Δ ↑ Δ ↓ › ≥ 0) e/ou "negativas" (‹ Δ ↑ Δ ↓ › ≤ 0) no nosso modelo. A generalização e reinterpretação do modelo de ilhas nos possibilitou (i) investigar flutuações dependentes de spin em correntes polarizadas; (ii) observar aumento e atenuação do shot noise; (iii) verificar que processos de "spin-flip" com (τ ↑ ↓ ≠ τ ↓ ↑) são relevantes na atenuação do shot noise e (iv) verificar que o ruído contém informações sobre o processo de "spin-flip"; In this work we investigate for the first time spin-dependent fluctuations in spin-polarized electronic currents through magnetic structures. Our physical model consists of a resonant-tunneling heterostructure formed by a Mn-based quantum well or "point"...

Time-dependent or state-dependent pricing? Evidence from a large devaluation episode

FELTRIN JR., CELIO; GUIMARAES, BERNARDO
Fonte: Fundação Getúlio Vargas Publicador: Fundação Getúlio Vargas
Tipo: Relatório
EN_US
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State-dependent and time-dependent price setting models yield distinct implications for how frequency and magnitude of price changes react to shocks. This note studies pricing behavior in Brazil following the large devaluation of the Brazilian Real in 1999 to distinguish between models. The results are consistent with state-dependent pricing

Time-dependent or state-dependent pricing? Evidence from firms’ response to inflation shocks

GUIMARAES, Bernardo; MAZINI, André; MENDONÇA, Diogo de Prince
Fonte: Fundação Getúlio Vargas Publicador: Fundação Getúlio Vargas
Tipo: Relatório
EN_US
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This paper proposes a test for distinguishing between time-dependent and state-dependent pricing based on whether the timing of pricing changes is affected by realized or expeted inflation. Using Brazilian data and exploring a large discrepancy between realized and expected inflation in 2002-3, we obtain a strong relation between expected inflation and duration of price spells, but little effect of inflation shocks on the frequency of price adjustment. The results thus support models with timedependent pricing, where the timing for following changes is optimally chosen whenever firms adjust prices

Coordinate and time-dependent diffusion dynamics in protein folding

Oliveira, Ronaldo J.; Whitford, Paul C.; Chahine, Jorge; Leite, Vitor B. P.; Wang, Jin
Fonte: Academic Press Inc. Elsevier B.V. Publicador: Academic Press Inc. Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 91-98
ENG
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); We developed both analytical and simulation methods to explore the diffusion dynamics in protein folding. We found the diffusion as a quantitative measure of escape from local traps along the protein folding funnel with chosen reaction coordinates has two remarkable effects on kinetics. At a fixed coordinate, local escape time depends on the distribution of barriers around it, therefore the diffusion is often time distributed. on the other hand, the environments (local escape barriers) change along the coordinates, therefore diffusion is coordinate dependent. The effects of time-dependent diffusion on folding can lead to non-exponential kinetics and non-Poisson statistics of folding time distribution. The effects of coordinate dependent diffusion on folding can lead to the change of the kinetic barrier height as well as the position of the corresponding transition state and therefore modify the folding kinetic rates as well as the kinetic routes. Our analytical models for folding are based on a generalized Fokker-Planck diffusion equation with diffusion coefficient both dependent on coordinate and time. Our simulation for folding are based on structure-based folding models with a specific fast folding protein CspTm studied experimentally on diffusion and folding with single molecules. The coordinate and time-dependent diffusion are especially important to be considered in fast folding and single molecule studies...

Structural basis for inhibition of cyclin-dependent kinase 9 by flavopiridol

Filgueira de Azevedo Jr., Walter; Canduri, Fernanda; Freitas da Silveira, Nelson José
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 566-571
ENG
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Flavopiridol has been shown to potently inhibit CDK1 and 2 (cyclin-dependent kinases 1 and 2) and most recently it has been found that it also inhibits CDK9. The complex CDK9-cyclin T1 controls the elongation phase of transcription by RNA polymerase II. The present work describes a molecular model for the binary complex CDK9-flavopiridol. This structural model indicates that the inhibitor strongly binds to the ATP-binding pocket of CDK9 and the structural comparison of the complex CDK2-flavopiridol correlates the structural differences with differences in inhibition of these CDKs by flavopiridol. This structure opens the possibility of testing new inhibitor families, in addition to new substituents for the already known leading structures such as flavones and adenine derivatives. © 2002 Elsevier Science (USA). All rights reserved.

Culture-dependent and culture-independent diversity surveys target different bacteria: a case study in a freshwater sample

Vaz-Moreira, Ivone; Egas, Conceição; Nunes, Olga C.; Manaia, Célia M.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2011 ENG
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Compared with culture-independent approaches, traditionally used culture-dependent methods have a limited capacity to characterizewatermicrobiota. Nevertheless, for almost a century the latter have been optimized to detect and quantify relevant bacteria. A pertinent question is if culture-independent diversity surveys give merely an extended perspective of the bacterial diversity or if, even with a higher coverage, focus on a different set of organisms. We compared the diversity and phylogeny of bacteria in a freshwater sample recovered by currently used culture-dependent and culture-independent methods (DGGE and 454 pyrosequencing). The culture-dependent diversity survey presented lower coverage than the other methods. However, it allowed bacterial identifications to the species level, in contrast with the other procedures that rarely produced identifications below the order. Although the predominant bacterial phyla detected by both approaches were the same (Proteobacteria, Actinobacteria, Bacteroidetes), sequence similarity analysis showed that, in general, different operational taxonomical units were targeted by each method. The observation that culture-dependent and independent approaches target different organisms has implications for the use of the latter for studies in which taxonomic identification has a predictive value. In comparison to DGGE...

Application of alternative regression models to deal with proportions as dependent variables

Marques, José Lourenço Pires
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em 09/03/2012 ENG
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Mestrado em Finanças; The main purpose of this thesis is to consider different approaches to deal with proportions as dependent variables in regression models. The Classical Linear Regression Model (CLRM) is the approach that most researchers apply to their data. However, the CLRM is inappropriate to deal with bounded variables whose response is restricted into the interval (0, 1) as dependent variables since it may possibly yield fitted values for the variable of interest that surpass its lower and upper limits. Due to the CLRM weaknesses, in this thesis we will consider some alternative parametric regression models that include the additive logistic normal distribution, the censored normal distribution, the Beta distribution and the normal distribution with nonlinear response function. A quasi-parametric regression approach will also be considered. In the empirical case we consider a dataset with financial information from US firms. The dependent variable of the models we intend to estimate is the debt to maturity, which is measured as a proportion of the total debt of the firm that has a maturity larger than three years. The explanatory variables are the abnormal earnings, the asset maturity and the size of the firm. To compare the above models will be used the Akaike’s information criterion (AIC) and Schwarz criterion (SBC). The distribution that displays the lowest values on both criteria is the best to study proportions as dependent variables. We will also study the adjusted value of each model.; Com esta tese pretendem-se considerar vários modelos de regressão alternativos ao lidar com proporções...

The role of Ca2+/calmodulin-dependent protein kinase II and calcineurin in TNF-α-induced myocardial hypertrophy

Wang,Gui-Jun; Wang,Hong-Xin; Yao,Yu-Sheng; Guo,Lian-Yi; Liu,Pei
Fonte: Associação Brasileira de Divulgação Científica Publicador: Associação Brasileira de Divulgação Científica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/11/2012 EN
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We investigated whether Ca2+/calmodulin-dependent kinase II (CaMKII) and calcineurin (CaN) are involved in myocardial hypertrophy induced by tumor necrosis factor α (TNF-α). The cardiomyocytes of neonatal Wistar rats (1-2 days old) were cultured and stimulated by TNF-α (100 μg/L), and Ca2+ signal transduction was blocked by several antagonists, including BAPTA (4 µM), KN-93 (0.2 µM) and cyclosporin A (CsA, 0.2 µM). Protein content, protein synthesis, cardiomyocyte volumes, [Ca2+]i transients, CaMKIIδB and CaN were evaluated by the Lowry method, [³H]-leucine incorporation, a computerized image analysis system, a Till imaging system, and Western blot analysis, respectively. TNF-α induced a significant increase in protein content in a dose-dependent manner from 10 µg/L (53.56 µg protein/well) to 100 μg/L (72.18 µg protein/well), and in a time-dependent manner from 12 h (37.42 µg protein/well) to 72 h (42.81 µg protein/well). TNF-α (100 μg/L) significantly increased the amplitude of spontaneous [Ca2+]i transients, the total protein content, cell size, and [³H]-leucine incorporation in cultured cardiomyocytes, which was abolished by 4 µM BAPTA, an intracellular Ca2+ chelator. The increases in protein content...

Effects of temperature-dependent viscosity on fluid flow and heat transfer in a helical rectangular duct with a finite pitch

Wang,Cuihua; Liu,Shengju; Wu,Jianhua; Li,Zhang
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2014 EN
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An incompressible fully developed laminar flow in a helical rectangular duct having finite pitch and curvature with temperature-dependent viscosity under heating condition is studied in this work. Both the cases of one wall heated and four walls heated are studied. The cross-sectional dimensions of the rectangular duct are 2a and 2b. The aspect ratio n=2b/2a is 0.5. Water is used as the fluid and Reynolds number (Re) is varied in the range of 100 to 400. The secondary flow with temperature-dependent viscosity is enhanced markedly as compared to constant viscosity. An additional pair of vortices is obtained near the center of the outer wall at Re=400 for the model of four walls heated with temperature-dependent viscosity, y, while for constant viscosity, the appearance of two additional vortices near the outer wall cannot be found. Besides, the axial velocity decreases and the temperature increases at the central region of the rectangular duct when the temperature-dependent viscosity is considered. Due to the decrease of the viscosity near the walls, the friction factor obtained with temperature-dependent viscosity is lower than that of constant viscosity, while the convective heat transfer for temperature-dependent viscosity is significantly enhanced owing to the strengthened secondary flow. Especially for four heated walls...

New statistical methods to assess the effect of time-dependent exposures in case-control studies

Cao, Zhirong
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
EN
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Contexte. Les études cas-témoins sont très fréquemment utilisées par les épidémiologistes pour évaluer l’impact de certaines expositions sur une maladie particulière. Ces expositions peuvent être représentées par plusieurs variables dépendant du temps, et de nouvelles méthodes sont nécessaires pour estimer de manière précise leurs effets. En effet, la régression logistique qui est la méthode conventionnelle pour analyser les données cas-témoins ne tient pas directement compte des changements de valeurs des covariables au cours du temps. Par opposition, les méthodes d’analyse des données de survie telles que le modèle de Cox à risques instantanés proportionnels peuvent directement incorporer des covariables dépendant du temps représentant les histoires individuelles d’exposition. Cependant, cela nécessite de manipuler les ensembles de sujets à risque avec précaution à cause du sur-échantillonnage des cas, en comparaison avec les témoins, dans les études cas-témoins. Comme montré dans une étude de simulation précédente, la définition optimale des ensembles de sujets à risque pour l’analyse des données cas-témoins reste encore à être élucidée, et à être étudiée dans le cas des variables dépendant du temps. Objectif: L’objectif général est de proposer et d’étudier de nouvelles versions du modèle de Cox pour estimer l’impact d’expositions variant dans le temps dans les études cas-témoins...

Calcium-dependent K current in plasma membranes of dermal cells of developing bean cotyledons

Zhang, W.H.; Walker, N.; Patrick, J.; Tyerman, S.
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Publicado em //2004 EN
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In developing seeds of bean (Phaseolus vulgaris L.), phloem-imported assimilates (largely sucrose and potassium) are released from coats to seed apoplasm and subsequently retrieved by the dermal cell complexes of cotyledons. To investigate the mechanisms of K⁺ uptake by the cotyledons, protoplasts of dermal cell complexes were isolated and whole-cell currents across their plasma membranes were measured with the patch-clamp technique. A weakly rectified cation current displaying a voltage-dependent blockade by external Ca²⁺ and acidic pH, dominated the conductance of the protoplasts. The P haseolus v ulgaris Cotyledon Dermal-cell pH and Calcium-dependent Cation Conductance (Pv-CD-pHCaCC) was highly selective for K⁺ over Ca²⁺ and Cl⁻. For K⁺ current through Pv-CD-pHCaCC a sigmoid shaped current–voltage (I–V) curve was observed with negative conductance at voltages between −200 and −140 mV. This negative K⁺ conductance was Ca²⁺ dependent. With other univalent cations (Na⁺, Rb⁺, NH₄⁺) the currents were smaller and were not Ca²⁺ dependent. Reversal potentials remained constant when external K⁺ was substituted with these cations, suggesting that Pv-CD-pHCaCC channels were non-selective. The Pv-CD-pHCaCC would provide a pathway for K⁺ and other univalent cation influx into developing cotyledons. These cation influxes could be co-ordinated with sucrose influx via pH and Ca²⁺ dependence.

Einfluss von Homocystein auf die endothelabhängige Gefäßrelaxation bei normalen und Streptozotocin induzierten diabetischen Ratten; Effects of homocysteine on endothelium dependent relaxation in control and streptozotocin-induced diabetic rats

Häntschel, Eva Natalie
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
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Sowohl Diabetes mellitus als auch Hyperhomocysteinämie (HHcy) werden in Zusammenhang mit der Entwicklung endothelialer Dysfunktion diskutiert. Ob die Verminderung des Methylierungspotentials (MP) bei erhöhtem Homocystein-Spiegel für die Entwicklung endothelialer Schädigungen verantwortlich ist, wurde in dieser Studie mittels Hemmung der S-Adenosylhomocystein-Hydrolase überprüft. Des Weiteren wurde die Wirkung des simultanen Bestehens von Typ 1 Diabetes und HHcy im Tiermodell auf die endothelabhängige Relaxation (EDR) untersucht, wobei es zu folgenden Ergebnissen kam: 1. Homocystein (Hcy) wirkt in konzentrationsabhängiger Weise hemmend auf die endothelabhängige Vasorelaxation, die endothelunabhängige Relaxation bleibt unverändert. 2. Die Inkubation von Aortenringen mit Adenosin-2´,3´-Dialdehyd (Adodia) resultiert in einer konzentrations- und zeitabhängigen Abschwächung der endothelabhängigen Relaxation, was auf einen möglichen Zusammenhang zwischen vermindertem MP und Beeinträchtigung der endothelabhängigen Relaxationsfähigkeit hindeutet. 3. Die simultane Inkubation der Gefäßsegmente mit Hcy und Adenosin für eine Stunde gefolgt von Adodia für 10 min (je 100 µM) zeigte denselben schwächenden Effekt auf die EDR wie die alleinige Inkubation mit Homocystein (100 µM) für eine Stunde. 4. Streptozotocin-induzierter Diabetes mellitus führte nach einem Zeitraum von vier Wochen zu einer unveränderten maximalen endothelabhängigen sowie –unabhängigen Relaxation gegenüber der Kontrolle. 5. Eine experimentell induzierte HHcy resultierte in einer abgeschwächten EDR sowie einer unbeeinträchtigten endothelunabhängigen Relaxation. 6. Das zeitgleiche Bestehen von Typ 1 Diabetes mellitus und HHcy führte nach vierwöchiger Erkrankungsdauer zu einer verminderten...

A Computer Language Transformation System Capable of Generalized Context-Dependent Parsing

Thurston, Adrian
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 739299 bytes; application/pdf
EN; EN
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Source transformation systems are special-purpose programming languages, or in some cases suites of languages, that are designed for the analysis and transformation of computer languages. They enable rapid prototyping of programming languages, source code renovation, language-to-language translation, design recovery, and other custom analysis techniques. With the emergence of these systems a serious problem is evident: expressing a parser for common computer languages is sometimes very difficult. Source transformation systems employ generalized parsing algorithms, and while these are well suited for the kind of agile parsing techniques in use by transformation practitioners, they are not well suited for parsing languages that are context-dependent. Traditional deterministic parser generators do not stumble in this area, but they sacrifice the generalized parsing abilities that transformation systems depend on. When it is hard to get the input into the system as a correct and accurate parse tree the utility of the unified transformation environment is degraded and more ad hoc approaches become attractive for processing input. This thesis is about the design of a new computer language transformation system with a focus on enhancing the parsing system to support generalized context-dependent parsing. We argue for the use of backtracking LR as the generalized parsing algorithm. We present an enhancement to backtracking LR that allows us to control the parsing of an ambiguous grammar by ordering the productions of the grammar definitions. We add a grammar-dependent lexical solution and integrate it with our ordered choice parsing strategy. We design a transformation language that is closer to general-purpose programming languages...

The ADP-dependent Sugar Kinase Family: Kinetic and Evolutionary Aspects

Merino, Felipe; Guixé Leguía, Victoria Cristina
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artículo de revista
EN
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Artículo de publicación ISI; Some archaea of the Euryarchaeota present a unique version of the Embden–Meyerhof pathway where glucose and fructose- 6-phosphate are phoshporylated using ADP instead of ATP as the phosphoryl donor. These are the only ADP-dependent kinases known to date. Although initially they were believed to represent a new protein family, they can be classified as members of the ribokinase superfamily, which also include several ATP-dependent kinases. As they were first identified in members of the thermococcales it was proposed that the presence of these ADP-dependent kinases is an adaptation to high temperatures. Later, homologs of these enzymes were identified in the genomes of mesophilic and thermophilic methanogenic archaea and even in the genomes of higher eukaryotes, suggesting that the presence of these proteins is not related to the hyperthermophilic life. The ADP-dependent kinases are very restrictive to their ligands being unable to use triphosphorylated nucleotides such as ATP. However, it has been shown that they can bind ATP by competition kinetic experiments. The hyperthermophilic methanogenic archaeon Methanocaldococcus jannaschii has a homolog of these genes, which can phosphorylate glucose and fructose-6- phosphate. For this reason...

Novel Modes of Regulation of Cyclin Dependent Kinase Cdk1

Zeng, Fanli
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis; info:eu-repo/semantics/publishedVersion
Publicado em //2014 ENG
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Les quinases dependents de ciclina (CDKs) dirigeixen la progressió del cicle cel·lular a les cèl·lules eucariotes. A l'organisme eucariota model Saccharomyces cerevisiae (llevat de gemmació) una sola quinasa dependent de ciclina, Cdk1, és essencial i suficient per dirigir el cicle cel·lular. Unida alternativament a ciclines de fase G1, S i G2/M, Cdk1 regula els programes transcripcionals del cicle cel·lular, la replicació i segregació dels cromosomes, la dinàmica del fus mitòtic, el creixement cel·lular polar, la morfogènesi, etc. La desregulació de l'activitat CDK promou la proliferació descontrolada i la inestabilitat genòmica. Donada la seva funció essencial en la progressió del cicle cel·lular, Cdk1 és estretament regulada per proteïnes associades (les ciclines, Cks1, i inhibidors de les CDKs –CKIs) i per modificacions post-traduccionals. Tanmateix, molts detalls de la regulació de Cdk1 romanen desconeguts, com és el cas de com les activitats CDK de fase G1 o de fase M són inhibides en resposta a determinats estressos cel·lulars. Quan la progressió del cicle cel·lular és amenaçada per la presència d'estressos genotòxics tals com l'estrès replicatiu o la presència de dany al DNA, un mecanisme de vigilància...

The effect of ICK1, a plant cyclin dependent kinase inhibitor, on mitosis in living plant cells

Cleary, Ann L; Fowke, L; Wang, Hong; John, Peter Crook
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
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The inhibitory activity of Arabidopsis thaliana ICK1, a plant cyclin-dependent kinase inhibitor, has previously been characterised by its effect on plant cyclin-dependent kinase activity in vitro and its effect on growth in transgenic plants. Herein, we examine cyclin-dependent kinase-driven cell-cycle events, probed by testing the sensitivity of living cells to introduced ICK1 protein. The microinjection of ICK1 into individual Tradescantia virginiana stamen hair cells during late prophase and prometaphase resulted in a clear protein-specific increase in the metaphase transit time (time from nuclear envelope breakdown to the onset of anaphase) in a manner dependent on load and injection time. The results indicate a continuing role for cyclin-dependent kinases in mitotic progression and provide in vivo evidence at the cellular level that ICK1 can restrict growth in the plant by inhibiting cell division.

Modulation of voltage-dependant Ba2+ currents in the guinea-pig gastric antrum by cyclic nucleotide-dependent pathways

Zhu, Hai-Lei; Hirst, George; Ito, Yushi; Teramoto, Noriyoshi
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
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We have investigated whether the activation of cAMP- and cGMP-dependent pathways modifies the properties of voltage-dependent Ba 2+ currents (I Ba) recorded from guinea-pig gastric myocytes using patch-clamp techniques. All experiments were carried on single smooth muscle cells, dispersed from the circular layer of the guinea-pig gastric antrum. Both dibutyryl cAMP (db-cAMP, 0.1-1 mM), a membrane-permeable ester of cAMP, and isoproterenol, a selective β-stimulant, inhibited I Ba in a concentration-dependent manner. Forskolin, but not dideoxy-forskolin, an inactive isomer of forskolin, inhibited the peak amplitude of I Ba. In the presence of either Rp-cAMP or the PKA (cAMP-dependent protein kinase) inhibitor peptide 5-24 (PKA-IP), neither forskolin nor db-cAMP inhibited I Ba. After establishing a conventional whole-cell recording, the peak amplitude of I Ba gradually decreased when the catalytic subunit of PKA was included in the pipette. The further application of Rp-cAMP reversibly enhanced I Ba. Sodium nitroprusside (0.1-1 mM) and 8-Br-cGMP (0.1-1 mM) also inhibited I Ba in a concentration-dependent manner. The inhibitory effects of forskolin or db-cAMP on I Ba were not significantly changed by pretreatment with a cGMP-dependent protein kinase (PKG) inhibitor. Similarly...