2009年03月25日

telomerase RNA

Telomeres cap the ends of chromosomes and provide a means to complete replication. The DNA portion of telomeres is synthesized by the enzyme telomerase using part of an RNA subunit as a tenplate for reverse transcription. How the mature 3' end of telomerase RNA is generated has so far remained elusive.

Here we show that in Schizosaccharomyces pombe telomerase RNA transcriots must be rocessed to generate functional telomerase. Charecterization of the maturation pathway uncovered un unexpected role for the spliceosome, which normally catalyses splicing of pre-messenger RNA.

The first spliceosomal cleavage reaction generates the mature 3' end of telomerase RNA (TER1, the functional RNA encoded by the ter1^+ gene), releasing the active from of the RNA without exon ligation.

Blocking the first step or permitting completion of spllicing generates inactive forms of TER1 and causes progressive telomere shortening.

We establish that 3'end processing of TER1 is critical for telomerase function and describe a previously unknown mechanism for RNA maturation that uses the ability of the spliceosome to mediate site-specific cleavage.


### DataBace ###
nature Vol.456 837-1008 no.7224
Spliceosome meets tekimerase / Sophie Bonnal & Juan Valacarcel
Spliceosomal clavage generates the 3' end of telomerase RNA / J A Box et al. (Stowers Institure for Medical Research)

posted by 0≠素子 at 09:46| Comment(0) | biogeochemistry | このブログの読者になる | 更新情報をチェックする

2009年03月21日

Reassessing the first appearance of eukaryotes and cyanobacteria

The evolution of oxygenic photosynthesis had a profound impact on the Earth's surface chemistry, leading to sharp rise in atomo-spheric oxygen between 2.45 and 2.32 billion years (Gyr) ago and the onset of extreme ice ages.(Beekker,A. at al. Dating the rise of atmospheric oxygen. nature427,117-120/2004)(Canfield,D.E The early history of atmospheric oxygen annu. Rev. Earth Planet. Sci. 33,1-36/2005)(Kopp,R.E., Kirschvink, J.L., Hilburn,I.A. &Nash,C.Z. The Paleoproterozoic snowball Earth : a climate disaster triggered by the evolution of oxygenic photosynthesis.Proc. Natl Acad. Sci. USA 102,11131-11136/2005)

The oldest widely accepted evidace for oxygenic photosynthesis has come from hydorocarbons extracted from 〜2.7-Gyr-old shales in the Pilbara Craton, Australia,whicth contain traces of biomarkers (molecular fossils) indicative of eukaryotes and suggestive of oxygen-producing cyanobacteria.(brocks,J.J., Logan,G.A., Buick,R. & Summons,R.E. Archean molecular fossils and the early rise of eukaryotes. Science 285,1033-1036/1999)(Brocks,J.J., Logan,G.A., Buick,R. & Summons,R.E. Composition and sungeneity of molecular fossils from the 2.38 to 2.45 billion-year-old Mount Bruce Supergroup, Pilbara Craton, Western Australia. Geochim. Cosmochim. Acta 67,4289-4319-/2003)(Brocks,J.J., Buick,R., Summons, R. E. & G. A. A reconstruction of Archean biological diversity based on molecular fossils from the 2.78 to 2.45 billion-year-old Mount Bruce Supergroup, Hamersley Basin, Western Australia. Geochim. Cosmochim. Acta 67,4321-4335/2003)(Simmons,R.E., Jahnke,L.L., Hope,J.M. & Logan,G.A. 2-Methylhopanoids as biomarkers for cyanobacterial oxygenic photosynthesis. Nature 400,554-557/1999)

The soluble hydrocarbons were interpreted to be indigenous and syngentic despite metamorphic alteration and extreme enrichment (10-20‰) of ^13~C relative to bulk sedimentary organic matter.(Brocks,J.J., Logan,G.A., Buick,R. & Summons,R.E. Composition and sungeneity of molecular fossils from the 2.38 to 2.45 billion-year-old Mount Bruce Supergroup, Pilbara Craton, Western Australia. Geochim. Cosmochim. Acta 67,4289-4319-/2003)(Heyes, J.M., Kaplan,I.R> & Wedeking,K.W. in Earth's Earliest Biosphere : Its Oligin and Evolution / Ed. Schopf,J.W / 93-134 / Princeton Iniv. Press,1983)

Here we present micrometre-scale, in situ ^13~C/^12~C measurements of pyrobitumen (thermally altered petroleum) and kerogen from these metamorphosed shales, including samples that priginally yielded biomarkers.

Our results show that both kerogen and pyrobitumen are stotongly depleted in ^13~C, indicating that indigenous petroleum is 10-20‰ lighter than the extracted hydrocarbons.(brocks,J.J., Logan,G.A., Buick,R. & Summons,R.E. Composition and sungeneity of molecular fossils from the 2.38 to 2.45 billion-year-old Mount Bruce Supergroup, Pilbara Craton, Western Australia. Geochim. Cosmochim. Acta 67,4289-4319-/2003)

These ersults are inconsistent with an indigenous origin for the biomarkers.

Whatever their origin, the biomarkers must have entered the rock after peak metamorphism 〜2.2Gyr ago and thusdo not provide evidence for the existence of eukaryotes and cyanobacteria in the Archaean eon.(Rasmussen,B., Fletcher,I.R. & Sheppard,S. Isotopic dating of the migration of a low-grade metamorphic front during orogensis. Geology 33,773-776/2005)

The old est fossil evidence for eukaryotes and cyanobacteria therefore reverts to 1.78-1.68Gyr ago and 〜2.15Gyr ago, respectively(Knoll,A.H., Javaux, E.J., Hewitt,D & Cohen, P. Eukarryyotic organisms in Proterrozoic oceans. Phil. Trans R. Soc. B 361,1023-1038/2006)(Hofmann,H.J. Precambrian microflora, Belcher Lslands, Canada:Significance and systematics. J.Paleontol, 50,1040-1073/1976)

Our results eliminate the evidence for oxygenic photosynthesis 〜2.7Gyr ago and exclude previous biomarker evidence for a long delay (〜300 million years) between the appearance of oxygen-producing cyanobacteria and tha rise in atmospheric axygen 2.45-2.32Gyr ago.(Beekker,A. at al. Dating the rise of atmospheric oxygen. nature427,117-120/2004)


### DataBace ###
nature Vol.445 1007-1148 Issue no.7216 23 October 2008
Letter p.1101 / Reassessing the first appearance of eukaryotes and cyanobacteria / B Rasmussen et al. (Cartin Univercity of technology)


posted by 0≠素子 at 12:26| Comment(0) | evolution | このブログの読者になる | 更新情報をチェックする

2009年03月19日

Life before the rise of oxgen

The discovery og molecular fossils in 2.7-billion-year-old rocks prompted are-evaluation og microbial evolution, and of the advent of photosynthesis and rize of atmospheric oxgen.

That discovery now comes into question.


Go Back to Archaean time, the interval of Earth's History between about 4 billion and 2.5 bilion years ago, and we're in largely unknown biological territory.

Attenpts to identifly a fossil recorf of life have prodused meager ersults. and controversy presists obout whether certain microfossil-like structuress are of biological orgin.(Schopf,J.W.Phill Trans. R. Soc B.361-869-885/2006)(Brasier,M.D.et.al. Nature416,76-81/2002)

Almost a decade ago, however, Archaean palaeontology received a big boost with the discovery by Brocks et al. of a diverse assenblage og lipid 'biomarkers' in 2.7-billion year-old geological samples from Western Australia.

Biomarkers, or molecular fossils, are natural products (often hydrocarbons) whose synthesis can be linked to a specific biological origin - and, by physiological proxy, to enbiron mental conditions.

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2009年03月15日

Oxidation in transtion

Many important biological and chemical processes, including photocatalytic water oxydation to molecular oxgen (of interrest as a route to artifical photosynthesis) and the activation of dioxygen on metal surfaces, are thought to involve transition metal terminal oxo complexes.

Poverenv et al. now report the synthersis of a platinum-based oxdizing reagent with potentially uzeful characteristics.

It's d^6 Pt(IV) terminal oxo complex that is not stabilized by anelectron accepting ligand framework, and so exhivits reactivity as both an inter-and intra-molecular oxygen donor and as an electrophile.

It also undergoes water activation to produce a terminal dihydroxo complex, which may be of relevance to the mechanism of water oxidation and other catalytic reactions.

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2009年03月14日

Plant invaders

The current episode of climate warming is resulting in range shifts of some plants and animals from lower to hugher latitudes and altitudes.

A study of the growth of fifteen plant species - six that had shoen rapid range expansion and nine related natives - now shows that exotic plant species expanding therir range into North-Western Europe will have less exposure than natives to both below-ground enemies and above-ground generalist herbivores.

One implication of this work is that some of the plants shifting their range towards higher katitudes and altitudes will be invasive with potential deleterious effects on biodiversity in temperate and notrthern latitudes.


### DataBace ###
nature Vol.456 837-1008 Issue no.7224


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2009年03月12日

Patteerning of sodium ions and the control of electrons in sodium bobaltate

Sodium cobaltate (NaxCoO2) has emierged as material of exceptional scientific interest due to the potential for thermoelectric applications, and because the strong interplay between the magnetic and superconducting properties has led to close comparisons with the physis of the superconducting copper oxides.(Terasaki,I., Sasago,Y., & Uchinokuma,K. Large thermoelectic power in NaxCoO2 single crystals. Phys. Rev. B56, R12685-12687/1997)(Lee,M.et al. Large enhancement of the thermopower in NaxCoO2 at high Na doing Nture Mater. 5,537-540/2006)(Takada,K. et al. Superconductivity in tow-dimensional NaxCoO2 layers. Nature 422,53-55/2003)

The densty x of the sodium in the intercalation layers can be altered electrochemically, directly changing the number of conduction electrons on the triangular Co layers.(Dalmas,C. et al Electrochemical interclation of sodium in NaxCoO2 bronzes. Soild State lonics 3/4,165-169/1981)

Recent electron diffraction measurements revel a kaleidoscope of Na^+ ion patterns as a function of concentration.(Zandbergen,H.W. et al. Sodium ion ordering in NaxCoO2 : Electron diffraction study. Phys. Rev. B70, 024101/2004)

Here we use single-crystal neutron diffraction supported by numerical simulations to determine the long-rage three-dimensional superstructures of these ions.

We are goveerned by pure electrostaties, and that the origanizational principle is the stabilization of charge droplets that order long range at some simple fractional fillings.

Our results provide a good startingpoint to understand the electronic properties in terms of a Hubbard hamiltonian that takes into account the electrostaric potential from the Na superstructures.(Hubbard,J, Electron correlations in narrow energy bands. Proc. R. Soc Land. A276,238-257/1963)

The resulting depth of potential wells in the Co layer is greater than the single-particle hopping kinetic energy and as a consequence, holes perferentially occupy the lowest potential regions.

Thus we conclude that the Na^+ ion patterning has a decisive role in the transpot and magnatic properties.


### DataBace ###
nature Vol.445 567-682 Issue no.7128 8 Febuary 2007
Letter p.631 / Patteerning of sodium ions and the control of electrons in sodium bobaltate / M Roger et al. (CEA Saclay)

posted by 0≠素子 at 04:16| Comment(0) | matter physics | このブログの読者になる | 更新情報をチェックする

STRUCTURL BIOLOGY : Molecular mecanichnery in action

If biology were a car, structural biologists would be looking under the bonnet to find out how the engine works.

Put more prosaically, structural biology aims to understand how biology works at the molecular level.

Much information is gleaned by studying at atomic resolution the three-dimensional structurs of molecules that make up living organisms, and the interactions of these molecules with one another.


### DataBace ###
nature Vol.445 567-682 Issue no.7128 8 Febuary 2007
News and Views p.609 / STRUCTURL BIOLOGY : Molecular mecanichnery in action / Ad Bax and Dennis A. Torchia
Articles p.618 / Quantitative dynamics and binding studies of the 20S proteasome by NMR / R Sprangers & L E Kay (The Universuty of Tronto)


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posted by 0≠素子 at 00:10| Comment(0) | sturacuture - biology | このブログの読者になる | 更新情報をチェックする

2009年03月05日

Earthquaks : the endgame

Once on Earthquake has been initiated the question arises, where will it end ? Hou big an earthque will it be? Analysis of the mapped surface rupture trances of 22 historical strike-slip earthquaks, the first at San Andreas, California in 1857 and the moust reccent at Denali, Alaska in 2002, Shows that rupture endpoints frequenty coincide with fault steps or the termini of active fault traces, and that a fault step of more than 3 or 4 km effectively stops an earthquake rupture in tracks.

These findings are relevant to seismic hazard analysis by suggesting limits on the probable extent of future earthquaks on known active faults.


### DataBace ###
nature Vol.444 243-400 Issue no.7117 16 November 2007
News and Views p.276 / SEISMOLOGY : Greatness Thrust upon then / James F. Doldan
Letter p.358 / Predicting the endpoints of earthquake rupturs / Steven G. Wesnousky (University of Nevada)

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posted by 0≠素子 at 10:07| Comment(0) | quantum information | このブログの読者になる | 更新情報をチェックする

Pandemic potential

The fact that the H5N1 bird flu virus circulating in Asia, Europe and Africa is unable to attach to fuman-type cell receptors has heleped to prevent it from causing world-wide epidemic of a human viriant of the disease.

Now a study of H5N1 isolates from some of the new humans that have been identified two mutations in a virlhaemagglutinin that allow it toboth human and avain receptors.

These mutations might be of use as molecular markers for assesing the pandemic potential of H5N1.


### DataBace ###
nature Vol.444 243-400 Issue no.7117 16 November 2007
Letter p.378 / Haemagglutinin mutations responsible for the bunding of H5N1 influenza A Viruses to human-type receptors / S Yamada (University of Tokyo, Japan Science and Technology Agency)/ www.nature.com/podcast


posted by 0≠素子 at 09:39| Comment(1) | diary | このブログの読者になる | 更新情報をチェックする

complement : The risks

from "TAKE 5 : Save handling of nanotechnoiogy".

As research leaders in our respective fields, we recognize that systematic risk research is need if emerging nano-industries are to thrive.

We cannot set the international reserch agenda on our own, but can inspire the scientific community - including government, industry, academia and other stakeholders - to move in the right direction.

So we prppose five grand callenges to stimulate research that is imaginative, innvative and avove all relevant to the safery of nanotechnology.

Fears over the possible dangers of somme nanotechnologyes may be exaggerated, but they are not necessarily unfounded.

Recent studies examiming the toxicity of engineered nanomaterials in cell cultures and animals have shown that size, surface area, surface chemistry solubility and possibly shape all play a role in determining the potential for engineerd nano-meterials to couse harm.(Oberdorster,G., Oberdorster,E. & Oberdorster, J. Environ Health Perspect. 13,823-840/2005)

This is not suprising : we have known for many years that inhaled dusts cause disease, and that their harmfulness depends on both what they are made of and their physical nature.

For instance, small particles of inhaled quartz lead to lung damage and the potential development of progressive lung disease, yet the same particles with a thin coating of clay are less harmful.(Donaldson,K. & Borm,P.J.A.Ann. Occup.Hyg. 42,287-294/1998)

Asbestos presents a far more dramatic example : thin, long fibress of the material can lead to lung disease if inhaled, but grind the fibres down to shorter particles with the same chemical make-up and the harmful ness is signficantly reduced.(Davis, J. G. et al. Br. J. Exp. Pathol. 67,415-430/1986)

It is generally accepted that, in principle, some nanomaterials may have the potential to cause harm to people and the enbironment.

But the way science is done is often ill-equipped to address novel ridks associated with emerging technologyes.

Reserch into understanding and preventing risk often has a low priority in the compertitive worlds of intellectual property, research funding and technology development.

And yet there is much at stake in how potential nano-specific riskes are understood and managed.

without strategic and targeted risk research, people producing and using nano-materials could develop unanticipated illness arising from their exposure ; public confidence in nanotechnoligies could be reduced through real or perceived dangers ; and fears of litigation may make nanotechnologies less attractive to investors and the insurance industry.


(...to be continue...)


### DataBace ###
nature Vol.444 243-400 Issue no.7117 16 November 2007
Commentary p.267 / Save handling of nanotechnoiogy / Andrew D. Maynard

posted by 0≠素子 at 02:05| Comment(0) | nanotechnology | このブログの読者になる | 更新情報をチェックする

2009年03月04日

TAKE 5 : Save handling of nanotechnoiogy

The pursuit og responsible nanotechnologies can be tackled through a series of grand challengs, argue Andrew D. Maynard and his co-authors.

When the physist and Nobel laureate Richard Feynman challenged the science community to think small in his 1959 lecture 'There's Plenty of Room at The Bottom', he planted the seeds of a new era in science and technology.

Nanotechnology, which is about controlling matter at near-atomic scals to produce unique or enhanced materials, products and devices, is now maturing rapidly with more than 300 claimed nanotechnology products already on the market.(The Nanotechnology Consumer Products Inventory / Washington DC,2006/Published online at -www.nanotechproject.org/consimerproducts)

Yet concerns have been raised that the very properties of nanostructured materials that make them so attractive could potentially lead to unforeseen health or environmental hazards.(Nsnoscience and Nanotechnologies : Opportunities and Uncertainties / The RoyalSociety and The Royal Academy of Engineering, London,2004)

The spectre of possible harm - whether real or imagined - is threatening to slow the development of nanotechnology unless sound, independent and authoritative information is developed on what the risk are, and how to aboid them.(Takling Action on Nanotech Environmental, Health and safety Risks / Lux Research, New York,2006)

In what may be unprecedented pre-emptive action in the face of a new technology, governments,industries and research organizations around the world are beginning to address how the benefits of emerging nanotechnologies can be realized while while minimizing potential risks.(Report of the OECD Workshop on the safety of Manufactured Nanomaterials : Building Co-operation and Communication / Organization for Economic Co-operation and Develoment,Paris,2006)

Yet despite a clear commitment to support risk-focused ersearch,opportunities to establish collaborative, integrated and targeted reserch programies are being missed .(Maynard,A.D Nanotechnology : A Research Strategy for Addressing Risk / Woodrw Wilson International Center for Scholars, washington DC,2006)

In september, Sherwood Boehlert, chair of the US House Sience Commitee, commented in a hearing that "we're on the right path to dealing with the problem, but we're sauntering down it when it when a sense of urgency is required".

And in October, Britain's Royal Society reised concerns that the UK government had not made enough progerss on reducing the uncertain ties surrounding the health and environmental impacts of nanomaterials.(Two-Year Review of Progress on Government Actions : Joint Academies'Response to the Council for Science and Technology's Call for Evidence / The Royal Society and the Royal Academy of Engineering, London,2006)


### DataBace ###
nature Vol.444 243-400 Issue no.7117 16 November 2007
Commentary p.267 / Save handling of nanotechnoiogy / Andrew D. Maynard

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posted by 0≠素子 at 03:37| Comment(0) | nanotechnology | このブログの読者になる | 更新情報をチェックする

2009年03月03日

Planetary gears

The Antikythera Mechaninm is an intricate bronze construction discovered damaged and fragmented in the wreck of a cargo ship pff the Greep island of Antikythera in 1900.

Made towards the end of the second century BC, it contains 30 bronza gear wheels and many astronomical isscriptions.

The mechanism is technically more complex than any known device for at least a millennium afterwords.

It acted as a lunar-solar calender, but its specific functions have remained controversial.

Now a joint British-Greek team has reconstructed the device based on surface imaging and X-ray tomography of the surviving fragments.

The reconstruction shows how the gears worked, and doubles the number of deciphered inscriptions.

The Mechanism seems to have been a sophisticated predictor for the Sun/Moon/Earth system, and can justfiably be caimed as the world's oldest known analogue computer.


### DataBace ###
nature Vol.444 519-652 Issue no.7119 30 November 2007
News Feature p.534 / Insearch of lost time / Jo Marchant reports.
News & Views p.551 / ARCHAEOGY : High thech from Ancient Greece / Francois Charette
Letter p.587 / Decoding the anciment Greek astronomical calculator known as the Antikythera Mechanism / T Freeth et al. (Cardiff University, Images First Ltd)

posted by 0≠素子 at 22:02| Comment(0) | archaeology | このブログの読者になる | 更新情報をチェックする

Structural basis for messenger RNA movement on the ribosome

Translation initiation is a major determinant of the overall expression level of a gene.(Gold,L. Posttranscriptional regulatory mechanisms in Escherichia coli. Annu. Rev. Biochem 57,199-233/1988)(Draper,D.E. in Eschericha coli and Salmonella : Cellular and Moecular Biology 2nd edn /eds Neidhardt,F.C. et al./902-908/ASM Press, Washington,DC,1996/)(Kozak,M. Regulation of translation via mRNA structure in prokaryotes and eukaryotes. Gene 361,13-37/2005)

The translation of functionally active protein requires the messenger RNA to be positioned on the ribosome such that the syart/initiation codon will be read first and in the correct frame.

Little is Known about the molecular basis for the interaction of mRNA with the ribosome at different states of translation.

Recent crystal structures of the ribosomal subunits (Wimberly,B.T. et al. structure of the 30S ribosomal subunit. Nature 407,327-339/2000)(Ogle,J.M. et al. Recognition of cognate transfar RNA by the 30S ribosomal subunit. Scrence 292,897-902/2001)(Ban,N. et al. The complete atomic structure of the large ribosomal subunit at 2.4 Å resolution. Science 289,905-920/2000)(Schluenzen,F. et al. Structure of functionally activated samall ribosomal subunit at 3.3 Å resolution. Cell 102,615-623/2000)(Haems,J. et al. High resolution structure of the large ribosomal subunit from a mesophilic eubacterium. Cell 107,679-688/2001), the empty 70S ribosome (Schuwirth,B.S. et al. structures of the bacterial ribosome at 3.5 Å resolution. Science 310,827-834/2005) and the 70S ribosome containing functional ligands (Yusupov,M.M. et al. Crystal structure of the ribosome at 5.5 Å resolution. Science 292,883-896/2001)(Yusupova,G.Z. et al. The path of messenger RNA through the ribosome. Cell 106, 233-241/2001)(Jenner,L. et al. Translational operator of mRNA on the ribosome : how reperssor proteins exclude ribosome binding. Science 308,120-123/2005)(Petry,S. et al. Crystal structures of the ribosome in complex with release factors RF1 and RF2 bound to a cognate stop codon. Cell 123, 1255-1266/2005) have provided information about the general organization of the robosome and its functional centres.

Hare we compare the X-ray structures of eight ribosome complexes modelling the translation initiation, post-initiation and elongation states.

In the initiation and post-initiation complexes, the presence of the Shine-Dalgarno (SD) duplex causes strong anchoring of the 5'- end of mRNA onto the platform of the 30S subunit, with numerous interactions between mRNA and the ribosome.

Conversely, the 5' end of the 'elongator' mRNA lacking SD interctions is flexible, suggesting a different exit path for mRNA during elongation.

After the initiation of translation, but while an SD interaction is still present, mRNA moves in the 3'→5' direction with simultaneous clockwise rotation and lengthening of the SD duplex, bringing it into contact with robosomal protein S2.


### DataBace ###
nature Vol.444 243-400 Issue no.7117 16 November 2007
Letters p.391 / Structural basis for messenger RNA movement on the ribosome / G Yusupova et al. (IGBMC)


posted by 0≠素子 at 12:15| Comment(0) | sturacuture - biology | このブログの読者になる | 更新情報をチェックする

STURUCTUAL BIOROGY : Dangerros liaisons on newrons

Crystal structures show that botulinum toxins bind simultaneously to two sites on neurons. This dual interaction allows them to use a trojan-horse strategy to enter nerve terminals, with deadly effect.

Botulinum neurotoxins (BoNTs) are some of the most deadly substances known to mankind. By blocking nerve function, they cause botulism, a severe condition that may ultimately lead to muscular and respiratory paralysis.

These sophisticated bacterial proteins owe their toxicity to their extraordinary specificity for neurons and to their enzymatic activity.

In this issue, papers by Jin et al. and Chai et al. describe the mechanisms by which BoNT/B - a toxin that causes human botulism - recognizes the surface of neuron junctions(syn apses - * This article and the papers concerned -were published online on 13 December 2006).(Jin,R., Rummel,A. Binz,A.T. Nature 444,1092-1095/2006)(Chai,Q. et al. Nature 444,1096-1100/2006)

This work provides insight in to how other BoNTs may exert their lethal action, and describes a mode of binding that night be used by other biological compounds.

Once inside a neuron, a single molecule of BoNT is, in principle, capable of deactivating the whole synapse. NoNTs consist of two protein segments, known, as the heavy and light chains.

IT is the light chain that deactivates neuromuscular junctions - the synapses that connect muscles to their contorolling neurons - by specifically inhibiting members of the SNARE protein family.(Schiavo,G., Matteoli, M. & Montecucco,C. Physiol. Rev. 717-766/2000).

SNARE proteins are distributed over the membranes of all animal and plant cells and are also found on the membranes of synaptic vesicles, the bubble-shaped organelles that store and release neurotrans-mitter chemicals at neuron terminals.

SNARE proteins are essential for membrane fusion, during which vesicles merge with the cell membrane and release their load. Once the synapticvesicles have done this, they are recycled by the neuron for further use.


### DataBace ###
nature Vol.444 243-400 Issue no.7117 16 November 2007
News and Vews p.1019/ STURUCTUAL BIOROGY : Dangerros liaisons on newrons / Giampietro Schiavo
Letters p.1092 / Botulinum newrotoxin B recognizes its protein receptor with high affinity and specificity / R Jin et al. (Stanfoed University)
Letters p,1096 / Structural basis of cell surface receptor recognition by botulinum newrotoxin B / Q Chai et al. (Scripps Research Institute)

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posted by 0≠素子 at 06:25| Comment(0) | sturacuture - biology | このブログの読者になる | 更新情報をチェックする

CONDENSED-MATTER PHYSICS : Let's twist agein

The spins of a layer of manganese atoms on a tungusten surface from a spiral pattern with a unique truning sense.

such 'chirial maganitic order' might exist in other, similar contexts, and have many useful applications.


Objects that differ from their mirror image - fuman hands, for instance - have a turn ing sense. This phenomenon of handedness, or chirality, is found in many natural contexts, from the elementary particles participating in electroweak interactions, via organic molecules and furricanes, all the way to galaxies.

Solids with a magnetic order of unique chirality could have many useful practical applications, becouse their peculiar symmetry allows the mixing of electronic, optical, magnetic and structural properties.

On page 190 of this isse, Bode et al. present compelling evidence for chiral magnetic order in a atrikingly simple solid-state system : a single layer of manganese atoms on a tungsten substrate.(Bode,M. et al. Nature 447,190-193/2007)

The authors achieved this by combining highly sophisticated, spin-sensitive scanning tunnelling micros-copy (STM) with an equally sophisticated first-principles calculation of the electronic structure of the manganese surface.

The amount of electrical current tunnelling from the manganese sample to the authors 'STM tip, which was coated with chromium or iron, depended on the electrons' derection of spin.

What Bode et al. observed was a long-period, spiral-shaped magnetic modulation of the STM intensity distoribution, superimposed on a basic antiferromagnetic structure (one in which adjacent spins point in opposite directions) .

When a magnetic field was applied, the pattern shifted in a given direction, identifying its unique chirality.


### DataBace ###
nature Vol.447 115-230 Issue no.7141 10 May 2007
News & Views p.157 /CONDENSED-MATTER PHYSICS : Let's twist agein / Cristien Pfleiderer and Urich K Robler
Letter p.190 / Chiral magnetic order at surfaces driven by inversion asymmetry / M Bode et al. (University of Hambrg)

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posted by 0≠素子 at 00:49| Comment(0) | condensed-matter physics | このブログの読者になる | 更新情報をチェックする

2009年03月01日

SEISMLOGY : Greatness thrust upon them

The latest research seems to imply that all earthquakes are born eaual. But combining that insight with earlier, seemingly contradictory, work could help us to tell which tremors grow to become more equal than others.

In an analysis on page 358 of this issue, Steven Wesnousky provides strong evidence that the ultimate size of a seismic ruputure is largely controlled by the structure of the underlyng fault, and therebefore that big earthquakes do not differ from small earthquakes in their beginnings.(Wesnousky,S.G et Nature444,358-360/2006)

These data might seen to conflict with earlier observations implying that the size of an earthquake is determined by the dynamics of ruputure onset.

In fact, both conclusions could be true, and combining these two data sets in future analyses of seismic hazards might result in a better prediction of the eventual size of an earthquake before the shaking stops.

Many Earth scientists have long suspected that the limit of an earthquake rupture, and therefore the magnitude of an event, is largely controlled by the structure of the fault zone and variations in stress along the fault itself.(Segall,P. & Pollard,D.D.J. Geophys.Res.85,4337-4350/1980)(Sibson,R.H. Nature316,248-251/1985)(Harris,R.A & Day,S.M,Geophys. Lett.26,2089-2092/1999)

In this view, all earthquakes begin in the same way, and continue to propagate until they reach a barrier, in the from of a structural complexity or a part of the fault on which the stresses are sufficiently low to stop rupture. Bur the alternative standpoint - that large earthquakes are in some way born differenty from their smaller brethren - is attractive becouse it holds thepromise of determining the evevntual size of anearthquake during the first fewseconds of the rupture.(Ellsworth, W.L. & Beroza, G. C. Science 268,851-855/1995)(Olsen,E.L. & Allen, R.M. Nature438,212-215/2005)

That could provide the basis for an wffective eary-waring system.


### DataBace ###
nature Vol.444 243-400 Issue no.7117 16 November 2007
News & Views p.276 / SEISMLOGY : Greatness thrust upon them / James F. Dolan
posted by 0≠素子 at 02:47| Comment(0) | earth | このブログの読者になる | 更新情報をチェックする

Rotation at faults

An early finding of the San Andress Fault Ovservatory at Depth (SAFOD) project, currently drilling an inclined borehole across the San Andreas Fault Zone to a 4-km depth, is that strees is rotated in the vicinity of the fault zoone.

Why this should occur here and at other similar 'weak' faults is not yet clear. A new model to help explain the phenomenon has been developed, based on field structure date of a large fault zone, lab measurements of rock elasticity, and numerical modelling.

The model suggests that is re-oriented around faults by the change in rock elasticity resulting from microscale damage produced by the fault.

### DataBace ###
nature Vol.454 789-970 Issue no.7121 14 December 2007
Letter p.922 / Slip on 'weak' faults by the rotation of regional stress in the fracture damage zone / D R Faulkner et al.(University of Liverpool)


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posted by 0≠素子 at 01:08| Comment(0) | earth | このブログの読者になる | 更新情報をチェックする
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