bluuebunny/crossref_metadata_2025 huggingface dataset:
Ordered Nucleation and Spreading of Silenced Chromatin inSaccharomyces cerevisiae
Authors: Rusché Laura N. , Kirchmaier Ann L. , Rine Jasper
Published: July 2002

In Saccharomyces cerevisiae, silencing at theHM loci depends on Sir proteins, which are structural components of silenced chromatin. To explore the structure and assembly of silenced chromatin, the associations of Sir proteins with sequences across the HMR locus were examined by chromatin immunoprecipitation. In wild-type cells, Sir2p, Sir3p, and Sir4p were spread throughout and coincident with the silenced region atHMR. Sir1p, in contrast, associated only with theHMR-E silencer, consistent with its role in establishment but not maintenance of silencing. Sir4p was required for the association of other Sir proteins with silencers. In contrast, in the absence of Sir2p or Sir3p, partial assemblies of Sir proteins could form at silencers, where Sir protein assembly began. Spreading acrossHMR required Sir2p and Sir3p, as well as the deacetylase activity of Sir2p. These data support a model for the spreading of silenced chromatin involving cycles of nucleosome deacetylation by Sir2p followed by recruitment of additional Sir2p, Sir3p, and Sir4p to the newly deacetylated nucleosome. This model suggests mechanisms for boundary formation, and for maintenance and inheritance of silenced chromatin. The principles are generalizable to other types of heritable chromatin states.
The chemical organization of signaling interactions
Authors: Bhalla Upinder S.
Published: July 2002

Motivation: Cellular chemical signaling pathways form complex networks that are beginning to be studied at the level of chemical kinetics and databases of reactions. Chemical reaction details are traditionally represented as lists of reactions and rates. This does not map readily to the block diagram representation familiar to biologists, and obscures the functional organization of signaling networks. This study examines motifs in signaling chemistry and reports common features that may help to formalize such a mapping between pathway block diagrams and the chemistry. The same motifs may facilitate data representation and provide functional abstraction of the chemistry.

Results: I classified 74 interactions between 25 signaling pathways in terms of shared chemical motifs. All interactions in this dataset consist of a few communicating molecules from one set of pathways, and a replicating set of reactions and molecules from another. Each unique combination of interacting pathways duplicates the chemical reaction scheme of this replicating set, but involves different rate constants. Signaling pathways can therefore be described in an object-oriented manner as sets of core reactions with well-defined interfaces between pathways. This generalization lends itself to designing simulators and databases for signaling networks.

Availability: Software and example models are freely available from http://www.ncbs.res.in/~bhalla/examples/EGFR_example.html

Contact: bhalla@ncbs.res.in

* To whom correspondence should be addressed.
Do Minimum Wages Fight Poverty?
Authors: Neumark David , Wascher William
Published: July 2002

We present evidence on the effects of minimum wages on family incomes. The results indicate that minimum wages increase both the probability that poor families escape poverty and the probability that previously nonpoor families fall into poverty. The estimated increase in the flow into poverty is larger, although this difference is not statistically significant. We also find that minimum wages tend to boost the incomes of poor families that remain below the poverty line. On net, the various trade‐offs created by minimum wage increases more closely resemble income redistribution among low‐income families than income redistribution from high‐ to low‐income families.
Scale Economies and the Dynamics of Recurring Auctions
Authors: Jeitschko Thomas D. , Wolfstetter Elmar
Published: July 2002

We analyze the dynamics of a game of sequential bidding in the presence of stochastic scale effects, either economies or diseconomies of scale. We show that economies of scale give rise to declining expected equilibrium prices, whereas the converse is not generally true. Moreover, first‐ and second‐price auctions are not always revenue equivalent. Economies of scale make second‐price auctions more profitable for the seller, whereas revenue equivalence may be preserved in the case of diseconomies.
The Confederate Constitution, Tariffs, and the Laffer Relationship
Authors: McGuire Robert A. , Van Cott T. Norman
Published: July 2002

This article offers an example of a national constitution, that of the Confederate States of America, which effectively constrained its fiscal authorities to tax rates on the lower end of the Laffer relationship. The taxes were Confederate import tariffs. Drawing on primary sources, the paper documents the role that this de facto capping of tariff rates played in the history of the drafting of the Confederate Constitution. That the Laffer relationship found constitutional expression for an important tax suggests that the “tariff” might have played a more significant role in the North–South conflict than is currently acknowledged.
International Charity: For the Poor?
Authors: Calmette Marie‐Françoise , Kilkenny Maureen
Published: July 2002

We show how international charity leads to reduced self‐help, exacerbated internal income inequality, and less charity for needy countries when international funds transfer is costly and there are information asymmetries. Mechanism design techniques are used to analyze international income transfer programs in the context of moral hazard, principal‐agent, and adverse selection problems. We show that the burden of information asymmetry is borne by the most needy even when charities design incentive contracts which limit informational rents.
Control of plant cytokinesis by an NPK1–mediated mitogen–activated protein kinase cascade
Authors: Soyano Takashi , Ishikawa Masaki , Nishihama Ryuichi , Araki Satoshi , Ito Mayumi , Ito Masaki , Machida Yasunori
Published: July 2002

Cytokinesis is the last essential step in the distribution of genetic information to daughter cells and partition of the cytoplasm. In plant cells, various proteins have been found in the phragmoplast, which corresponds to the cytokinetic apparatus, and in the cell plate, which corresponds to a new cross wall, but our understanding of the functions of these proteins in cytokinesis remains incomplete. Reverse genetic analysis of NPK1 MAPKKK (nucleus– and phragmoplast–localized protein kinase 1 mitogen–activated protein kinase kinase kinase) and investigations of factors that might be functionally related to NPK1 have helped to clarify new aspects of the mechanisms of cytokinesis in plant cells. In this review, we summarize the evidence for the involvement of NPK1 in cytokinesis. We also describe the characteristics of a kinesin–like protein and the homologue of a mitogen–activated protein kinase that we identified recently, and we discuss possible relationships among these proteins in cytokinesis.
Molecular basis of cold adaptation
Authors: D'Amico Salvino , Claverie Paule , Collins Tony , Georlette Daphné , Gratia Emmanuelle , Hoyoux Anne , Meuwis Marie-Alice , Feller Georges , Gerday Charles
Published: July 2002

Cold–adapted, or psychrophilic, organisms are able to thrive at low temperatures in permanently cold environments, which in fact characterize the greatest proportion of our planet. Psychrophiles include both prokaryotic and eukaryotic organisms and thus represent a significant proportion of the living world. These organisms produce cold–evolved enzymes that are partially able to cope with the reduction in chemical reaction rates induced by low temperatures. As a rule, cold–active enzymes display a high catalytic efficiency, associated however, with a low thermal stability. In most cases, the adaptation to cold is achieved through a reduction in the activation energy that possibly originates from an increased flexibility of either a selected area or of the overall protein structure. This enhanced plasticity seems in turn to be induced by the weak thermal stability of psychrophilic enzymes. The adaptation strategies are beginning to be understood thanks to recent advances in the elucidation of the molecular characteristics of cold–adapted enzymes derived from X–ray crystallography, protein engineering and biophysical methods. Psychrophilic organisms and their enzymes have, in recent years, increasingly attracted the attention of the scientific community due to their peculiar properties that render them particularly useful in investigating the possible relationship existing between stability, flexibility and specific activity and as valuable tools for biotechnological purposes.
Lysine methylation within the globular domain of histone H3 by Dot1 is important for telomeric silencing and Sir protein association
Authors: Ng Huck Hui , Feng Qin , Wang Hengbin , Erdjument-Bromage Hediye , Tempst Paul , Zhang Yi , Struhl Kevin
Published: July 2002

The amino-terminal histone tails are subject to covalent post-translational modifications such as acetylation, methylation, and phosphorylation. In the histone code hypothesis, these exposed and unstructured histone tails are accessible to a repertoire of regulatory factors that specifically recognize the various modified histones, thereby generating altered chromatin structures that mediate specific biological responses. Here, we report that lysine (Lys) 79 of histone H3, which resides in the globular domain, is methylated in eukaryotic organisms. In the yeast Saccharomyces cerevisiae, Lys 79 of histone H3 is methylated by Dot1, a protein shown previously to play a role in telomeric silencing. Mutations of Lys 79 of histone H3 and mutations that abolish the catalytic activity of Dot1 impair telomeric silencing, suggesting that Dot1 mediates telomeric silencing largely through methylation of Lys 79. This defect in telomeric silencing might reflect an interaction between Sir proteins and Lys 79, becausedot1 and Lys 79 mutations weaken the interaction of Sir2 and Sir3 with the telomeric region in vivo. Our results indicate that histone modifications in the core globular domain have important biological functions.
Spot 42 RNA mediates discoordinate expression of the E. coli galactose operon
Authors: Møller Thorleif , Franch Thomas , Udesen Christina , Gerdes Kenn , Valentin-Hansen Poul
Published: July 2002

The physiological role of Escherichia coli Spot 42 RNA has remained obscure, even though the 109-nucleotide RNA was discovered almost three decades ago. Structural features of Spot 42 RNA and previous work suggested to us that the RNA might be a regulator of discoordinate gene expression of the galactose operon, a control that is only understood at the phenomenological level. The effects of controlled expression of Spot 42 RNA or deleting the gene (spf) encoding the RNA supported this hypothesis. Down-regulation ofgalK expression, the third gene in the gal operon, was only observed in the presence of Spot 42 RNA and required growth conditions that caused derepression of the spf gene. Subsequent biochemical studies showed that Spot 42 RNA specifically bound at thegalK Shine-Dalgarno region of the galETKM mRNA, thereby blocking ribosome binding. We conclude that Spot 42 RNA is an antisense RNA that acts to differentially regulate genes that are expressed from the same transcription unit. Our results reveal an interesting mechanism by which the expression of a promoter distal gene in an operon can be modulated and underline the importance of antisense control in bacterial gene regulation.
Brn-1 and Brn-2 share crucial roles in the production and positioning of mouse neocortical neurons
Authors: Sugitani Yoshinobu , Nakai Shigeyasu , Minowa Osamu , Nishi Miyuki , Jishage Kou-ichi , Kawano Hitoshi , Mori Kensaku , Ogawa Masaharu , Noda Tetsuo
Published: July 2002

Formation of highly organized neocortical structure depends on the production and correct placement of the appropriate number and types of neurons. POU homeodomain proteins Brn-1 and Brn-2 are coexpressed in the developing neocortex, both in the late precursor cells and in the migrating neurons. Here we show that double disruption of bothBrn-1 and Brn-2 genes in mice leads to abnormal formation of the neocortex with dramatically reduced production of layer IV–II neurons and defective migration of neurons unable to express mDab1. These data indicate that Brn-1 and Brn-2 share roles in the production and positioning of neocortical neuron development.
Rap1–Sir4 binding independent of other Sir, yKu, or histone interactions initiates the assembly of telomeric heterochromatin in yeast
Authors: Luo Kunheng , Vega-Palas Miguel A. , Grunstein Michael
Published: July 2002

In Saccharomyces cerevisiae, heterochromatin-like regions are found near telomeres and at the silent mating-type loci, where they can repress genes in an epigenetic manner. Several proteins are involved in telomeric heterochromatin structure including Rap1, Sir2, Sir3, Sir4, yKu70 (Hdf1), yKu80 (Hdf2), and the N termini of histones H3 and H4. By recognizing cis-acting DNA-binding sites, Rap1 is believed to recruit Sir and other silencing proteins and determine where heterochromatin forms. The integrity of heterochromatin also requires the binding of Sir proteins to histones that may form a scaffold for Sir protein interactions with chromatin. In this study we describe how the heterochromatin complex may form initially and how it differs from the complex that spreads along the chromosome. We found that close to the telomere end, Sir4 can bind Rap1 independently of Sir2, Sir3, yKu70/yKu80, and the intact H4 N terminus. In contrast, Sir4 binding requires all of the silencing factors further along telomeric heterochromatin. These data indicate that Sir4 binding to Rap1 initiates the sequential association of Sir and other proteins, allowing the subsequent spreading of the heterochromatin proteins along the chromosome.
Successive Olfactory Reversal Learning in Honeybees
Authors: Komischke Bernhard , Giurfa Martin , Lachnit Harald , Malun Dagmar
Published: July 2002

HoneybeesApis melliferacan associate an originally neutral odor with a reinforcement of sucrose solution. Forward pairings of odor and reinforcement enable the odor to release the proboscis extension reflex in consecutive tests. Bees can also be conditioned differentially: They learn to respond to a reinforced odor and not to a nonreinforced one. They can also learn to reverse their choice. Here we ask whether honeybees can learn successive olfactory differential conditioning tasks involving different overlapping pairs of odors. The conditioning schedules were established in order to train the animals with 3, 2, 1, or 0 reversals previous to a last differential conditioning phase in which two additional reversals were present. We studied whether or not successive reversal learning is possible and whether or not learning olfactory discrimination reversals affects the solving of subsequent discrimination reversals. Therefore we compared the responses of bees that had experienced reversals with those of bees that had not experienced such reversals when both are confronted with a new reversal situation. In experiment 1 we showed that bees that had experienced three previous reversals were better in solving the final reversal task than bees with no previous reversal experience. In experiment 2, we showed that one reversal learning is enough for bees to perform better in the final reversal task. The successive different reversals trained in our experiments resemble the natural foraging situation in which a honeybee forager has to switch successively from an initial floral species to different ones. The fact that experiencing such changes seems to improve a bee's performance in dealing with further new exploited food sources has therefore an adaptive impact for the individual and for the colony as a whole.
Expression Profiling of Reciprocal Maize Hybrids Divergent for Cold Germination and Desiccation Tolerance
Authors: Kollipara Krishna P. , Saab Imad N. , Wych Robert D. , Lauer Michael J. , Singletary George W.
Published: July 2002

Recombinant inbred lines (RILs) derived from B73 × M017 were screened for cold germination (CG) and desiccation tolerance (DT) phenotypes. Reciprocal F1 hybrids were made between divergent RILs, and hybrids that showed differential phenotypes (parent-of-origin effect) for CG or DT were selected for profiling mRNA and protein expression. mRNA and proteins were extracted from embryo axes of seed germinated for 11 d at 12.5°C in the dark and developing embryos at 40% seed moisture (R5 stage) for CG and DT, respectively. GeneCalling analysis, an open-ended mRNA profiling method, identified 336 of 32,496 and 656 of 32,940 cDNA fragments that showed ≥1.5-fold change in expression between the reciprocal F1 hybrids for CG and DT, respectively. Protein expression map (PEM) analysis, an open-ended two-dimensional polyacrylamide gel electrophoresis, identified 117 of 2,641 and 205 of 1,876 detected proteins to be differentially expressed with ≥1.5-fold change between the reciprocal F1 hybrids in CG and DT samples, respectively. A subset of these proteins was identified by tandem mass spectrometry followed by database query of the spectra. The differentially expressed genes/proteins were classified into various functional groups including carbohydrate and amino acid metabolism, ion transporters, stress and defense response, polyamine metabolism, chaperonins, cytoskeleton associated, etc. Phenotypic analysis of seed from self-pollinated ears of the reciprocal F1 hybrids displayed small differences compared with the reciprocal hybrids themselves, suggesting a negligible effect of cytoplasmic factors on CG and DT traits. The results provide leads to improving our understanding of the genes involved in stress response during seed maturation and germination.
Influence of the Diadinoxanthin Pool Size on Photoprotection in the Marine Planktonic Diatom Phaeodactylum tricornutum
Authors: Lavaud Johann , Rousseau Bernard , van Gorkom Hans J. , Etienne Anne-Lise
Published: July 2002

The pool size of the xanthophyll cycle pigment diadinoxanthin (DD) in the diatom Phaeodactylum tricornutum depends on illumination conditions during culture. Intermittent light caused a doubling of the DD pool without significant change in other pigment contents and photosynthetic parameters, including the photosystem II (PSII) antenna size. On exposure to high-light intensity, extensive de-epoxidation of DD to diatoxanthin (DT) rapidly caused a very strong quenching of the maximum chlorophyll fluorescence yield (F  m, PSII reaction centers closed), which was fully reversed in the dark. The non-photochemical quenching of the minimum fluorescence yield (F  o, PSII centers open) decreased the quantum efficiency of PSII proportionally. For bothF  m and F  o, the non-photochemical quenching expressed asF/F′ − 1 (with F′ the quenched level) was proportional to the DT concentration. However, the quenching of F  o relative to that ofF  m was much stronger than random quenching in a homogeneous antenna could explain, showing that the rate of photochemical excitation trapping was limited by energy transfer to the reaction center rather than by charge separation. The cells can increase not only the amount of DT they can produce, but also its efficiency in competing with the PSII reaction center for excitation. The combined effect allowed intermittent light grown cells to down-regulate PSII by 90% and virtually eliminated photoinhibition by saturating light. The unusually rapid and effective photoprotection by the xanthophyll cycle in diatoms may help to explain their dominance in turbulent waters.
Remodeling of DNA Methylation and Phenotypic and Transcriptional Changes in Synthetic Arabidopsis Allotetraploids
Authors: Madlung Andreas , Masuelli Ricardo W. , Watson Brian , Reynolds Steve H. , Davison Jerry , Comai Luca
Published: July 2002

The joining of different genomes in allotetraploids played a major role in plant evolution, but the molecular implications of this event are poorly understood. In synthetic allotetraploids of Arabidopsis and Cardaminopsis arenosa, we previously demonstrated the occurrence of frequent gene silencing. To explore the involvement of epigenetic phenomena, we investigated the occurrence and effects of DNA methylation changes. Changes in DNA methylation patterns were more frequent in synthetic allotetraploids than in the parents. Treatment with 5-aza-2′-deoxycytidine, an inhibitor of DNA methyltransferase, resulted in the development of altered morphologies in the synthetic allotetraploids, but not in the parents. We profiled mRNAs in control and 5-aza-2′-deoxycytidine-treated parents and allotetraploids by amplified fragment length polymorphism-cDNA. We show that DNA demethylation induced and repressed two different transcriptomes. Our results are consistent with the hypothesis that synthetic allotetraploids have compromised mechanisms of epigenetic gene regulation.
Excess Copper Predisposes Photosystem II to Photoinhibition in Vivo by Outcompeting Iron and Causing Decrease in Leaf Chlorophyll
Authors: Pätsikkä Eija , Kairavuo Marja , Šeršen Frantisek , Aro Eva-Mari , Tyystjärvi Esa
Published: July 2002

Photoinhibition of photosystem II was studied in vivo with bean (Phaseolus vulgaris) plants grown in the presence of 0.3 (control), 4, or 15 μm Cu2+. Although photoinhibition, measured in the presence of lincomycin to block concurrent recovery, is faster in leaves of Cu2+-treated plants than in control leaves, thylakoids isolated from Cu-treated plants did not show high sensitivity to photoinhibition. Direct effects of excess Cu2+ on chloroplast metabolism are actually unlikely, because the Cu concentration of chloroplasts of Cu-treated plants was lower than that of their leaves. Excess Cu in the growth medium did not cause severe oxidative stress, collapse of antioxidative defenses, or loss of photoprotection. Thus, these hypothetical effects can be eliminated as causes for Cu-enhanced photoinhibition in intact leaves. However, Cu treatment lowered the leaf chlorophyll (Chl) concentration and reduced the thylakoid membrane network. The loss of Chl and sensitivity to photoinhibition could be overcome by adding excess Fe together with excess Cu to the growth medium. The addition of Fe lowered the Cu2+ concentration of the leaves, suggesting that Cu outcompetes Fe in Fe uptake. We suggest that the reduction of leaf Chl concentration, caused by the Cu-induced iron deficiency, causes the high photosensitivity of photosystem II in Cu2+-treated plants. A causal relationship between the susceptibility to photoinhibition and the leaf optical density was established in several plant species. Plant species adapted to high-light habitats apparently benefit from thick leaves because the rate of photoinhibition is directly proportional to light intensity, but photosynthesis becomes saturated by moderate light.
Targeting Tryptophan Decarboxylase to Selected Subcellular Compartments of Tobacco Plants Affects Enzyme Stability and in Vivo Function and Leads to a Lesion-Mimic Phenotype
Authors: Di Fiore Stefano , Li Qiurong , Leech Mark James , Schuster Flora , Emans Neil , Fischer Rainer , Schillberg Stefan
Published: July 2002

Tryptophan decarboxylase (TDC) is a cytosolic enzyme that catalyzes an early step of the terpenoid indole alkaloid biosynthetic pathway by decarboxylation of l-tryptophan to produce the protoalkaloid tryptamine. In the present study, recombinant TDC was targeted to the chloroplast, cytosol, and endoplasmic reticulum (ER) of tobacco (Nicotiana tabacum) plants to evaluate the effects of subcellular compartmentation on the accumulation of functional enzyme and its corresponding enzymatic product. TDC accumulation and in vivo function was significantly affected by the subcellular localization. Immunoblot analysis demonstrated that chloroplast-targeted TDC had improved accumulation and/or stability when compared with the cytosolic enzyme. Because ER-targeted TDC was not detectable by immunoblot analysis and tryptamine levels found in transient expression studies and in transgenic plants were low, it was concluded that the recombinant TDC was most likely unstable if ER retained. Targeting TDC to the chloroplast stroma resulted in the highest accumulation level of tryptamine so far reported in the literature for studies on heterologous TDC expression in tobacco. However, plants accumulating high levels of functional TDC in the chloroplast developed a lesion-mimic phenotype that was probably triggered by the relatively high accumulation of tryptamine in this compartment. We demonstrate that subcellular targeting may provide a useful strategy for enhancing accumulation and/or stability of enzymes involved in secondary metabolism and to divert metabolic flux toward desired end products. However, metabolic engineering of plants is a very demanding task because unexpected, and possibly unwanted, effects may be observed on plant metabolism and/or phenotype.
The White Clover enod40 Gene Family. Expression Patterns of Two Types of Genes Indicate a Role in Vascular Function
Authors: Varkonyi-Gasic Erika , White Derek William Richard
Published: July 2002

Enod40 is one of the genes associated with legume nodule development and has a putative role in general plant organogenesis. We have isolated a small enod40 gene family from white clover (Trifolium repens), with three genes designated Trenod40-1, Trenod40-2, and Trenod40-3, all containing the conservedenod40 regions I and II. Trenod40-1 andTrenod40-2 share over 90% homology in the transcribed regions and high levels of similarity in their upstream regulatory sequences. Trenod40-1 and Trenod40-2 are similar to the enod40 genes of legumes forming indeterminate nodules (group II) and are predominantly expressed in nodules. Trenod40-3 shares only 32.8% identity withTrenod40-1 and Trenod40-2 within the transcribed region. Trenod40-3 is similar to theenod40 genes of legumes with determinate nodules (group I) and is not predominantly expressed in nodules. To our knowledge, this is the first report of both group I- and group II-typeenod40 genes being expressed in a single legume species. In situ hybridization studies revealed that Trenod40genes were highly expressed in non-symbiotic tissues, particularly in stolon nodes during nodal root and lateral shoot development. High levels of Trenod40 transcripts were also present in the vascular bundles of mature plant organs, mainly at sites of intensive lateral transport, suggesting a role in vascular tissue function. The expression pattern of Trenod40 genes was analyzed further using Trenod40 promoter-gusfusions in transgenic white clover and tobacco (Nicotiana tabacum), indicating that white clover and tobacco share the regulatory mechanisms for Trenod40-1/2 promoters and some aspects of Trenod40-3 regulation.
Reorientation of Seedlings in the Earth's Gravitational Field Induces Cytosolic Calcium Transients
Authors: Plieth Christoph , Trewavas Anthony J.
Published: July 2002

The gravitational field controls plant growth, morphology, and development. However, the underlying transduction mechanisms are not well understood. Much indirect evidence has implicated the cytoplasmic free calcium concentration ([Ca2+]c) as an important factor, but direct evidence for changes in [Ca2+]c is currently lacking. We now have made measurements of [Ca2+]c in groups of young seedlings of Arabidopsis expressing aequorin in the cytoplasm and reconstituted in vivo with cp-coelenterazine, a synthetic high-affinity luminophore. Distinct [Ca2+]c signaling occurs in response to gravistimulation with kinetics very different from [Ca2+]c transients evoked by other mechanical stimuli (e.g. movement and wind). [Ca2+]cchanges produced in response to gravistimulation are transient but with a duration of many minutes and dependent on stimulus strength (i.e. the angle of displacement). The auxin transport blockers 2,3,5-tri-iodo benzoic acid and N-(1-naphthyl) phthalamic acid interfere with gravi-induced [Ca2+]cresponses and addition of methyl indole-3-acetic acid to whole seedlings induces long-lived [Ca2+]ctransients, suggesting that changes in auxin transport may interact with [Ca2+]c. Permanent nonaxial rotation of seedlings on a two-dimensional clinostat, however, produced a sustained elevation of the [Ca2+]c level. This probably reflects permanent displacement of gravity-sensing cellular components and/or disturbance of cytoskeletal tension. It is concluded that [Ca2+]c is part of the gravity transduction mechanism in young Arabidopsis seedlings.
A Cell Plate–Specific Callose Synthase and Its Interaction with Phragmoplastin
Authors: Hong Zonglie , Delauney Ashton J. , Verma Desh Pal S.
Published: July 2002

Callose is synthesized on the forming cell plate and several other locations in the plant. We cloned an Arabidopsis cDNA encoding a callose synthase (CalS1) catalytic subunit. The CalS1 gene comprises 42 exons with 41 introns and is transcribed into a 6.0-kb mRNA. The deduced peptide, with an approximate molecular mass of 226 kD, showed sequence homology with the yeast 1,3-β-glucan synthases and is distinct from plant cellulose synthases. CalS1 contains 16 predicted transmembrane helices with the N-terminal region and a large central loop facing the cytoplasm. CalS1 interacts with two cell plate–associated proteins, phragmoplastin and a novel UDP-glucose transferase that copurifies with the CalS complex. That CalS1 is a cell plate–specific enzyme is demonstrated by the observations that the green fluorescent protein–CalS1 fusion protein was localized at the growing cell plate, that expression of CalS1 in transgenic tobacco cells enhanced callose synthesis on the forming cell plate, and that these cell lines exhibited higher levels of CalS activity. These data also suggest that plant CalS may form a complex with UDP-glucose transferase to facilitate the transfer of substrate for callose synthesis.
The calculation of a parent grain orientation from inherited variants for approximate (b.c.c.–h.c.p.) orientation relations
Authors: Humbert M. , Gey N.
Published: July 2002

The orientations of parent β grains are evaluated from several α variants inherited from the same parent during the body-centred cubic (b.c.c.) to hexagonal close packed (h.c.p.) phase transformation. The proposed calculation, based on orientation correlating and orientation averaging, is particularly useful when the inherited variants are not strictly related to the parent orientation by a strict Burgers orientation relation or when the orientations of the inherited volumes vary slightly at different locations of the variant. This method of parent identification from variant orientations is an improvement of a previously published method.
Completion of crystal structure by powder diffraction data: a new method for locating atoms with polyhedral coordination
Authors: Giacovazzo Carmelo , Altomare Angela , Cuocci Corrado , Moliterni Anna Grazia Giuseppina , Rizzi Rosanna
Published: July 2002

Ab initiocrystal structure solutionviapowder diffraction data is often incomplete: frequently, the heavy atoms are correctly located but the light-atom positions are usually unreliable. The recently developed procedurePOLPO[Altomareet al.(2000).J. Appl. Cryst.33, 1305–1310], implemented in theEXPOprogram [Altomareet al.(1999).J. Appl. Cryst.32, 339–340], aims at completing a partial structure model provided by direct methods by exploiting the prior information on the polyhedral coordination of the located atoms (tetrahedral or octahedral) and their connectivity. ThePOLPOprocedure requires that all the cations are correctly labelled and rightly located. This condition does not always occur, particularly when the data quality is poor. A new method is described which is able to locate missing cations and surrounding anions when the cation coordination is tetrahedral or octahedral. The procedure has been successfully checked on different test structures.
Elimination of minimal FFT grid-size limitations
Authors: Langs David A.
Published: July 2002

The fast Fourier transform (FFT) algorithm as normally formulated allows one to compute the Fourier transform of up toNcomplex structure factors,F(h),N/2 ≥h> −N/2, if the transform ρ(r) is computed on anN-point grid. Most crystallographic FFT programs test the ranges of the Miller indices of the input data to ensure that the total number of grid divisions in thex,yandzdirections of the cell is sufficiently large enough to perform the FFT. This note calls attention to a simple remedy whereby an FFT can be used to compute the transform on as coarse a grid as one desires without loss of precision.
Three-dimensional Pt-nanoparticle networks studied by anomalous small-angle X-ray scattering and X-ray absorption spectroscopy
Authors: Vad T. , Haubold H.-G. , Waldöfner N. , Bönnemann H.
Published: July 2002

Anomalous small-angle X-ray scattering (ASAXS) experiments with synchrotron radiation were performed to study the three-dimensional nanostructures of metal/organic hybrids formed by crosslinking aluminium-organic-stabilized platinum nanoparticles with various bifunctional organic spacer molecules. The advantage of ASAXS is the possibility of separating the particle scattering from that of the organic components, thus providing unbiased information about particle size distributions and interparticle correlation. In order to obtain the structural information from the scattering data, a model function based on Vrij's analytical solution for a multicomponent system of hard spheres is proposed. The model is applied to three different samples and the results are compared with those obtained from the application of Fourier methods (characteristic function) and X-ray absorption measurements.
On the handling of atomic anisotropic displacement parameters
Authors: Grosse-Kunstleve R. W. , Adams P. D.
Published: July 2002

A number of conventions for the parameterization of atomic anisotropic displacements are used in the literature and in crystallographic programs. Here we summarize the commonly used conventions, with a special emphasis on their application in macromolecular crystallography. We then describe a new software toolbox for the handling of the various parameterizations of atomic anisotropic displacements and their interconversion. All algorithms are integrated into the freely availableComputational Crystallography Toolbox.
Modeling growth and equilibrium form of α-SiO2
Authors: Nicolov Mirela F. , Woensdregt Cornelis F.
Published: July 2002

The α phase of SiO2is known as a technologically important material. According to the Hartman–Perdok theory, so-calledFforms are present: the hexagonal prismm{10\bar{1}0}, the major rhombohedronr{10\bar{1}1} and the minor rhombohedronz{01\bar{1}1}.Ffaces grow according to a two-dimensional growth mechanism and are the only forms to be expected on the growth form. Computation of attachment energies, which are considered to be directly related to the growth rates of the correspondingFfaces, has been performed using an electrostatic point-charge model, taking into account Born repulsion and van der Waals contributions computed by means of the Gilbert equation or the van Beest and van Santen potential. All the theoretical growth forms are prismatic with the two aforementioned rhombohedra, which are almost equally important and independent of the corrections for the van der Waals and Born interactions. The equilibrium form is prismatic and shorter as a result of the hexagonal prism form being less important. On the atomic scale, the differences in surface topologies between theFforms depend on the variation in depth below the surface boundary of those central Si atoms that are partially unshielded because of the incomplete tetrahedral coordination.
Mapping of unstressed lattice parameters using pulsed neutron transmission diffraction
Authors: Santisteban Javier Roberto , Steuwer A. , Edwards L. , Withers P. J. , Fitzpatrick M. E.
Published: July 2002

Stress measurement by neutron diffraction depends critically on knowledge of the unstressed lattice parameter (a0) of the specimen under study. As a result, measurement of stress profiles in components wherea0is not homogeneous throughout the sample, such as welds or carburized surfaces, can be particularly difficult. An efficient solution to this problem is proposed based on the pulsed neutron transmission diffraction technique. This technique exploits the sharp steps in intensity, the so-called Bragg edges, appearing in the transmitted neutron spectra of polycrystalline materials, such steps being produced by coherent scattering from lattice planes. The position of these Bragg edges as defined by the time-of-flight technique is used to determine precisely local interplanar distances. In this work it is shown that the unstressed lattice parameter of thin specimens subjected to plane stress fields can be defined by recording transmission spectra at different sample inclinations, in complete analogy with the sin2ψ technique used in X-ray diffraction. Moreover, by using an array of detectors it is possible to produce a radiographic `image' ofa0for plane specimens or thin sections out of three-dimensional ones. The capability of the technique is exemplified by mapping the changes ina0for a ferritic weld that was used as a round robin sample in an international program for standardization of stress measurements by neutron diffraction.
The effect of the temperature change rate on determination of the critical pitting temperature of stainless steels
Authors: Krakowiak Stefan , Darowicki Kazimierz
Published: July 2002

Results have been presented of investigations on the effect of the temperature change rate on the critical temperature of pitting corrosion. Investigations of 316L stainless steel have been conducted by cyclic thermometry. An increase has been stated of the critical pitting temperature with increase of the temperature change rate. The dependence of the pitting critical temperature is linear in character for all investigated temperature change rates. Values of the critical temperature of pitting corrosion for stationary conditions (E−ES=0) were obtained by using the extrapolation procedure. The critical pitting temperature obtained by extrapolation practically does not depend on the temperature change rate in the investigated range and is equal to 336.9 K (63.9°C).
Imported Beer in the Hong Kong Market
Authors: Speece Mark W. , Kawahara Yukiko , So Stella L.M.
Published: July 2002

Argues that successful exporting to East Asian markets requires a good
understanding of local conditions. One important issue is how consumers
decide on products and how they view products from various countries.
Hong Kong is representative of newly affluent markets which are growing
throughout East Asia. In the beer market, Hong Kong consumers choose
brands based on quality characteristics, especially taste. Other
important aspects include the beer′s image and the country‐of‐origin.
Brand loyalty is strong. Price is relatively unimportant to most
consumers. Many beer drinkers believe that German beer is the best,
though they may not always buy beer from Germany.
Mutual Recognition and the Food Industries:
Authors: Swinbank Alan
Published: July 2002

Examines Article 30 EC which provides for the free movement of goods between the member states of the European Union. Following theCassis de Dijoncase the Commission of the European Communities articulated the principle of mutual recognition under which products lawfully manufactured and marketed in one member state should have unrestricted access to the markets of all member states. It now appears that Article 30 freedoms do not depend on the coupled requirement of manufacture and marketing, and that these freedoms would apply to any products lawfully marketed in the member states. This being so, Third Country products can presumably benefit from Article 30 freedoms, though many authors had previously thought they could not. Nonetheless much uncertainty remains regarding the application of mutual recognition to Third Country products.
Microbiological Hazards from Red Meat and Their Control
Authors: Mead Geoff C.
Published: July 2002

Contamination of red meat with foodborne pathogens is associated with
symptom‐less carriage of the organisms in the live animal. In the United
Kingdom, meat is an acknowledged source of human food poisoning from
Salmonella and Clostridium perfringens, and other pathogens that are
sometimes present may also be important in this respect. Within the EU,
much attention has been given to improving the design and structure of
abattoirs, although, in themselves, such changes do not ensure low
levels of microbial contamination. However, it has been suggested that,
with due care in slaughtering and meat handling, microbial counts from
carcasses can be reduced from around 103‐104 to 102‐103/cm2 and
that contamination with any foodborne pathogens can also be reduced.
Discusses those stages in meat handling which have the greatest effect
on carcass contamination and the importance of using a system of quality
assurance that incorporates the hazard analysis critical control point
concept (HACCP). As an adjunct to good abattoir hygiene, possible
processes for decontamination of finished carcasses, especially with hot
water or lactic acid, are considered.
Implementation of the Fresh Meat (Hygiene and Inspection) Regulations
1992
Authors: Hewson Peter
Published: July 2002

Explains how the implementation of the regulations was managed and how
the new system is risk‐based, with the emphasis placed on hygiene of
operation rather than on structural matters.
Food Hygiene Training: The Chance to Create a Coherent Policy
Authors: Smith Roger
Published: July 2002

In September this year, the Government issued its draft Regulations on
Food Safety (General Food Hygiene) 1995, which acknowledges for the
first time the importance of a programme to make food handlers, their
supervisors and managers, properly aware of the importance of food
hygiene for the protection of the consumer and what they can do to
prepare food safely. However, the regulation is specific neither about
how training should best be implemented nor on the most important aspect
of the policy, its end result. The standards of food hygiene awareness
to be achieved through training have not been specified. The Department
of Health, and the Ministry of Agriculture, Fisheries and Food (MAFF)
cannot delegate their responsibility to protect the public health.
Therefore, levels of food hygiene awareness, regardless of industrial
sector, should be their prime concern. If the departments could set
their minimum required standard of food hygiene awareness, the national
framework of training which has evolved could naturally regulate the
quality of training itself.
Knowledge, attitudes and eating habits of teenagers with respect to
salt in their diet
Authors: North Sadie L. , Neale Roger J.
Published: July 2002

Secondary school children′s knowledge, attitudes and eating habits
towards dietary salt (NaC1) were measured by self‐completed
questionnaires in schools in Nottinghamshire (East Midlands of England)
and analysed on the basis of age and sex. The results showed that a very
high proportion (86 to 98 per cent) of children (both boys and girls)
add salt to foods, with approximately 70 per cent of the younger
children adding salt before tasting. The most popular food to which salt
was added was chips (94 per cent of all children) and the least popular
were pasta, soup and salad. The majority of the children perceived their
own salt intake as medium in level, but this perception did not
discriminate between added salt and salt present in processed food,
about which their knowledge was fairly poor. Comparison of the sodium
(Na) content of pastry samples produced by an in‐house recipe in several
Nottingham schools showed them to vary five‐fold, but in every case
except one they were lower than the Na level of a commercial pastry mix
marketed to school meals authorities. Consideration should be given to a
substantial reduction in Na contents of a range of both in‐house recipe
foods and prepacked processed foods provided to children in school
meals.
Meat inspection costs ‐ a charge too far?
Authors: Thompson Katharine , Upson Joan
Published: July 2002

Presents the recent case of Woodspring District Council v. Bakers of Nailsea Ltd which has highlighted several contentious points of EU legislation for the meat industry, especially the cost of abattoir inspections. EU law states that these inspections should be carried out by official veterinary surgeons thus incurring great cost. Bakers of Nailsea contended that these inspections could have been done by qualified meat inspectors at a greatly reduced cost. Proposes that, although the judge ruled against Bakers of Nailsea, this case has implications for other similar cases. Discusses EU Directives and Regulations concerning food safety and hygiene.
Fat content and sponge cake quality
Authors: Seaman Claire E.A. , Woods Maggie , MacKenzie Dionne
Published: July 2002

Reports a recipe modification exercise which was undertaken to determine whether an acceptable sponge cake could be produced using low‐fat spreads in place of full‐fat margarine or butter. The textural and sensory qualities of the cakes were studied and a price analysis carried out to identify price differences between low‐fat and full‐fat spreads. Presents results which indicate that, as the fat content of cakes decreases, the sensory quality also decreases, although an acceptable product can be produced using a spread containing 65 per cent fat. Finds that low‐fat spreads are in many cases more expensive than their full‐fat equivalents. Highlights the need for further work to identify a fat replacer which can be used successfully in baking.
Customer‐supplier relationships in the UK trade of rice
Authors: Hogg Annik , Kalafatis Stavros P. , Blankson Charles
Published: July 2002

Deals with some issues associated with relationship‐forming patterns within the UK trade of rice. In particular examines the importance of 16 variables, through a telephone survey, at three levels of the distribution chain, millers/ importers, manufacturers and retailers. The results indicate an overall uniformity in the importance of the variables between the channel intermediaries. In relative terms, finds soft/ personal variables to be perceived as less important than hard/product‐related variables. Furthermore, consistent with existing literature, identifies the following relationship‐forming groups of variables: interpersonal or intanintegrative criteria, relationship monitoring criteria, price criteria and product criteria.
The supply chains of perishable products in northern Europe
Authors: Wilson Natasha
Published: July 2002

Looks at the concept of supply chain management, discussing the theory and its relevance to perishables distribution and marketing. Shows how supply chain management (SCM) moves on from neoclassical theories of the firm to a new paradigm for business where competition pits channel against channel, and where supply chain partners combine skills and resources which none of the participants would be able to achieve independently. Argues that a growing recognition of the competitive advantage that can be gained through improving co‐ordination in the supply chain is the starting point for SCM initiatives that are evolving in the fresh produce sector. Observes that the fruit and vegetable supply chain has traditionally been fragmented but the last decade has seen rapid structural change. Briefly analyses the results of a qualitative survey of several northern European markets, in context, to highlight the differing degrees of pipeline integration within each system.