Subscribe: Science: Current IssueScience: This Week's NewsThis Week in ScienceEditors' ChoiceNetWatchScience Magazine PodcastScienceNOW
http://sciencenow.sciencemag.org/rss/current.xml
Added By: Feedage Forager Feedage Grade C rated
Language: English
Tags:
black hole  chiral  electron  exon ligation  exon  human  kidney  ligation  magnetic  model  ndash  rubisco  splice site  structure 
Rate this Feed
Rate this feedRate this feedRate this feedRate this feedRate this feed
Rate this feed 1 starRate this feed 2 starRate this feed 3 starRate this feed 4 starRate this feed 5 star

Comments (0)

Feed Details and Statistics Feed Statistics
Preview: Science: Current IssueScience: This Week's NewsThis Week in ScienceEditors' ChoiceNetWatchScience Magazine PodcastScienceNOW

Science current issue



Science RSS feed -- current issue



 



Designing river flows to improve food security futures in the Lower Mekong Basin

2017-12-07T10:23:19-08:00

Rivers provide unrivaled opportunity for clean energy via hydropower, but little is known about the potential impact of dam-building on the food security these rivers provide. In tropical rivers, rainfall drives a periodic flood pulse fueling fish production and delivering nutrition to more than 150 million people worldwide. Hydropower will modulate this flood pulse, thereby threatening food security. We identified variance components of the Mekong River flood pulse that predict yield in one of the largest freshwater fisheries in the world. We used these variance components to design an algorithm for a managed hydrograph to explore future yields. This algorithm mimics attributes of discharge variance that drive fishery yield: prolonged low flows followed by a short flood pulse. Designed flows increased yield by a factor of 3.7 relative to historical hydrology. Managing desired components of discharge variance will lead to greater efficiency in the Lower Mekong Basin food system.




Harassment in science is real

2017-12-07T10:23:19-08:00




News at a glance

2017-12-07T10:23:19-08:00






















Last stands

2017-12-07T10:23:19-08:00




Best books for curious kids

2017-12-07T10:23:19-08:00




Can dams be designed for sustainability?

2017-12-07T10:23:19-08:00




Putting the RuBisCO pieces together

2017-12-07T10:23:19-08:00




Coherent nanoparticles in calcite

2017-12-07T10:23:19-08:00




TRP'ing up chronic kidney disease

2017-12-07T10:23:19-08:00




Concerns for ozone recovery

2017-12-07T10:23:19-08:00







EU can help Spain's endangered seabird

2017-12-07T10:23:19-08:00




Broad conservation: Protect the unknowns

2017-12-07T10:23:19-08:00




Quake warning funds on shaky ground

2017-12-07T10:23:19-08:00




Probing the metabolism of microorganisms

2017-12-07T10:23:19-08:00




Metabolic markers as cancer clues

2017-12-07T10:23:19-08:00




Reading the genome like a history book

2017-12-07T10:23:19-08:00







The flight of the narwhal

2017-12-07T10:23:19-08:00




Gaining a foothold on kidney disease?

2017-12-07T10:23:19-08:00




Conditions in a black hole outburst

2017-12-07T10:23:19-08:00




Watching electrons lose steam in graphene

2017-12-07T10:23:19-08:00




FAK directs tumor immune evasion

2017-12-07T10:23:19-08:00




Understanding splicing from the 3' end

2017-12-07T10:23:19-08:00




A sweet source to make acrylonitrile

2017-12-07T10:23:19-08:00




One cause of accidental deaths

2017-12-07T10:23:19-08:00




Taking a direct route to the brain

2017-12-07T10:23:19-08:00




The peopling of Asia

2017-12-07T10:23:19-08:00




Optimizing flow in dammed rivers

2017-12-07T10:23:19-08:00




Computer or human?

2017-12-07T10:23:19-08:00




Probing an excitonic condensate

2017-12-07T10:23:19-08:00




Building a brain

2017-12-07T10:23:19-08:00




A magnetic tip reconfigures edge states

2017-12-07T10:23:19-08:00




A biotech tour de force

2017-12-07T10:23:19-08:00




Clocking departures from chiral origins

2017-12-07T10:23:19-08:00




Many roads to being tough

2017-12-07T10:23:19-08:00




A source of methane in the upper ocean

2017-12-07T10:23:19-08:00




An even longer road to recovery?

2017-12-07T10:23:19-08:00




Priming T follicular helper cells

2017-12-07T10:23:19-08:00




Detecting skeletal growth

2017-12-07T10:23:19-08:00







Multifactorial response to drought

2017-12-07T10:23:19-08:00




The health hazards of fiber intake

2017-12-07T10:23:19-08:00




Downplaying versus embracing differences

2017-12-07T10:23:19-08:00




The metabolic needs of migrating Tregs

2017-12-07T10:23:19-08:00




Softly getting a grip

2017-12-07T10:23:19-08:00




Pulling versus heating

2017-12-07T10:23:19-08:00




Plant RuBisCo assembly in E. coli with five chloroplast chaperones including BSD2

2017-12-07T10:23:19-08:00

Plant RuBisCo, a complex of eight large and eight small subunits, catalyzes the fixation of CO2 in photosynthesis. The low catalytic efficiency of RuBisCo provides strong motivation to reengineer the enzyme with the goal of increasing crop yields. However, genetic manipulation has been hampered by the failure to express plant RuBisCo in a bacterial host. We achieved the functional expression of Arabidopsis thaliana RuBisCo in Escherichia coli by coexpressing multiple chloroplast chaperones. These include the chaperonins Cpn60/Cpn20, RuBisCo accumulation factors 1 and 2, RbcX, and bundle-sheath defective-2 (BSD2). Our structural and functional analysis revealed the role of BSD2 in stabilizing an end-state assembly intermediate of eight RuBisCo large subunits until the small subunits become available. The ability to produce plant RuBisCo recombinantly will facilitate efforts to improve the enzyme through mutagenesis.




Structure of the yeast spliceosomal postcatalytic P complex

2017-12-07T10:23:19-08:00

The spliceosome undergoes dramatic changes in a splicing cycle. Structures of B, Bact, C, C*, and intron lariat spliceosome complexes revealed mechanisms of 5'–splice site (ss) recognition, branching, and intron release, but lacked information on 3'-ss recognition, exon ligation, and exon release. Here we report a cryo–electron microscopy structure of the postcatalytic P complex at 3.3-angstrom resolution, revealing that the 3' ss is mainly recognized through non–Watson-Crick base pairing with the 5' ss and branch point. Furthermore, one or more unidentified proteins become stably associated with the P complex, securing the 3' exon and potentially regulating activity of the helicase Prp22. Prp22 binds nucleotides 15 to 21 in the 3' exon, enabling it to pull the intron-exon or ligated exons in a 3' to 5' direction to achieve 3'-ss proofreading or exon release, respectively.




Postcatalytic spliceosome structure reveals mechanism of 3'-splice site selection

2017-12-07T10:23:19-08:00

Introns are removed from eukaryotic messenger RNA precursors by the spliceosome in two transesterification reactions—branching and exon ligation. The mechanism of 3'–splice site recognition during exon ligation has remained unclear. Here we present the 3.7-angstrom cryo–electron microscopy structure of the yeast P-complex spliceosome immediately after exon ligation. The 3'–splice site AG dinucleotide is recognized through non–Watson-Crick pairing with the 5' splice site and the branch-point adenosine. After the branching reaction, protein factors work together to remodel the spliceosome and stabilize a conformation competent for 3'–splice site docking, thereby promoting exon ligation. The structure accounts for the strict conservation of the GU and AG dinucleotides at the 5' and 3' ends of introns and provides insight into the catalytic mechanism of exon ligation.




Attosecond-resolved photoionization of chiral molecules

2017-12-07T10:23:19-08:00

Chiral light-matter interactions have been investigated for two centuries, leading to the discovery of many chiroptical processes used for discrimination of enantiomers. Whereas most chiroptical effects result from a response of bound electrons, photoionization can produce much stronger chiral signals that manifest as asymmetries in the angular distribution of the photoelectrons along the light-propagation axis. We implemented self-referenced attosecond photoelectron interferometry to measure the temporal profile of the forward and backward electron wave packets emitted upon photoionization of camphor by circularly polarized laser pulses. We measured a delay between electrons ejected forward and backward, which depends on the ejection angle and reaches 24 attoseconds. The asymmetric temporal shape of electron wave packets emitted through an autoionizing state further reveals the chiral character of strongly correlated electronic dynamics.




Coherently aligned nanoparticles within a biogenic single crystal: A biological prestressing strategy

2017-12-07T10:23:19-08:00

In contrast to synthetic materials, materials produced by organisms are formed in ambient conditions and with a limited selection of elements. Nevertheless, living organisms reveal elegant strategies for achieving specific functions, ranging from skeletal support to mastication, from sensors and defensive tools to optical function. Using state-of-the-art characterization techniques, we present a biostrategy for strengthening and toughening the otherwise brittle calcite optical lenses found in the brittlestar Ophiocoma wendtii. This intriguing process uses coherent nanoprecipitates to induce compressive stresses on the host matrix, functionally resembling the Guinier–Preston zones known in classical metallurgy. We believe that these calcitic nanoparticles, being rich in magnesium, segregate during or just after transformation from amorphous to crystalline phase, similarly to segregation behavior from a supersaturated quenched alloy.




A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni

2017-12-07T10:23:19-08:00

Observations of binary stars containing an accreting black hole or neutron star often show x-ray emission extending to high energies (>10 kilo­–electron volts), which is ascribed to an accretion disk corona of energetic particles akin to those seen in the solar corona. Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its 2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the corona. This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems.




Imaging resonant dissipation from individual atomic defects in graphene

2017-12-07T10:23:19-08:00

Conversion of electric current into heat involves microscopic processes that operate on nanometer length scales and release minute amounts of power. Although central to our understanding of the electrical properties of materials, individual mediators of energy dissipation have so far eluded direct observation. Using scanning nanothermometry with submicrokelvin sensitivity, we visualized and controlled phonon emission from individual atomic-scale defects in graphene. The inferred electron-phonon "cooling power spectrum" exhibits sharp peaks when the Fermi level comes into resonance with electronic quasi-bound states at such defects. Rare in the bulk but abundant at graphene’s edges, switchable atomic-scale phonon emitters provide the dominant dissipation mechanism. Our work offers insights for addressing key materials challenges in modern electronics and enables control of dissipation at the nanoscale.




Renewable acrylonitrile production

2017-12-07T10:23:19-08:00

Acrylonitrile (ACN) is a petroleum-derived compound used in resins, polymers, acrylics, and carbon fiber. We present a process for renewable ACN production using 3-hydroxypropionic acid (3-HP), which can be produced microbially from sugars. The process achieves ACN molar yields exceeding 90% from ethyl 3-hydroxypropanoate (ethyl 3-HP) via dehydration and nitrilation with ammonia over an inexpensive titanium dioxide solid acid catalyst. We further describe an integrated process modeled at scale that is based on this chemistry and achieves near-quantitative ACN yields (98 ± 2%) from ethyl acrylate. This endothermic approach eliminates runaway reaction hazards and achieves higher yields than the standard propylene ammoxidation process. Avoidance of hydrogen cyanide as a by-product also improves process safety and mitigates product handling requirements.




Quantized chiral edge conduction on domain walls of a magnetic topological insulator

2017-12-07T10:23:19-08:00

Electronic ordering in magnetic and dielectric materials forms domains with different signs of order parameters. The control of configuration and motion of the domain walls (DWs) enables nonvolatile responses against minute external fields. Here, we realize chiral edge states (CESs) on the magnetic DWs of a magnetic topological insulator. We design and fabricate the magnetic domains in the quantum anomalous Hall state with the tip of a magnetic force microscope and prove the existence of the chiral one-dimensional edge conduction along the prescribed DWs through transport measurements. The proof-of-concept devices based on reconfigurable CESs and Landauer-Büttiker formalism are realized for multiple-domain configurations with well-defined DW channels. Our results may lead to the realization of low-power-consumption spintronic devices.




Signatures of exciton condensation in a transition metal dichalcogenide

2017-12-07T10:23:19-08:00

Bose condensation has shaped our understanding of macroscopic quantum phenomena, having been realized in superconductors, atomic gases, and liquid helium. Excitons are bosons that have been predicted to condense into either a superfluid or an insulating electronic crystal. Using the recently developed technique of momentum-resolved electron energy-loss spectroscopy (M-EELS), we studied electronic collective modes in the transition metal dichalcogenide semimetal 1T-TiSe2. Near the phase-transition temperature (190 kelvin), the energy of the electronic mode fell to zero at nonzero momentum, indicating dynamical slowing of plasma fluctuations and crystallization of the valence electrons into an exciton condensate. Our study provides compelling evidence for exciton condensation in a three-dimensional solid and establishes M-EELS as a versatile technique sensitive to valence band excitations in quantum materials.




Spatiotemporal gene expression trajectories reveal developmental hierarchies of the human cortex

2017-12-07T10:23:19-08:00

Systematic analyses of spatiotemporal gene expression trajectories during organogenesis have been challenging because diverse cell types at different stages of maturation and differentiation coexist in the emerging tissues. We identified discrete cell types as well as temporally and spatially restricted trajectories of radial glia maturation and neurogenesis in developing human telencephalon. These lineage-specific trajectories reveal the expression of neurogenic transcription factors in early radial glia and enriched activation of mammalian target of rapamycin signaling in outer radial glia. Across cortical areas, modest transcriptional differences among radial glia cascade into robust typological distinctions among maturing neurons. Together, our results support a mixed model of topographical, typological, and temporal hierarchies governing cell-type diversity in the developing human telencephalon, including distinct excitatory lineages emerging in rostral and caudal cerebral cortex.




Firearms and accidental deaths: Evidence from the aftermath of the Sandy Hook school shooting

2017-12-07T10:23:19-08:00

Exposure to firearms increased substantially after the December 2012 shooting at Sandy Hook Elementary School in Newtown, Connecticut, where 20 children and 6 adults were killed. Gun sales spiked by 3 million, on the basis of the increase in the number of background checks for firearm purchases. Google searches for buying and cleaning guns increased. We used Vital Statistics mortality data to examine whether a spike in accidental firearm deaths occurred at the same time as the greater exposure to firearms. We also assessed whether the increase in these deaths was larger in those states where the spike in gun sales per capita was larger. We find that an additional 60 deaths overall, including 20 children, resulted from unintentional shootings in the immediate aftermath of Sandy Hook.




Paradoxical escape responses by narwhals (Monodon monoceros)

2017-12-07T10:23:19-08:00

Until recent declines in Arctic sea ice levels, narwhals (Monodon monoceros) have lived in relative isolation from human perturbation and sustained predation pressures. The resulting naïvety has made this cryptic, deep-diving cetacean highly susceptible to disturbance, although quantifiable effects have been lacking. We deployed a submersible, animal-borne electrocardiograph-accelerometer-depth recorder to monitor physiological and behavioral responses of East Greenland narwhals after release from net entanglement and stranding. Escaping narwhals displayed a paradoxical cardiovascular down-regulation (extreme bradycardia with heart rate ≤4 beats per minute) superimposed on exercise up-regulation (stroke frequency >25 strokes per minute and energetic costs three to six times the resting rate of energy expenditure) that rapidly depleted onboard oxygen stores. We attribute this unusual reaction to opposing cardiovascular signals—from diving, exercise, and neurocognitive fear responses—that challenge physiological homeostasis.




A small-molecule inhibitor of TRPC5 ion channels suppresses progressive kidney disease in animal models

2017-12-07T10:23:19-08:00

Progressive kidney diseases are often associated with scarring of the kidney’s filtration unit, a condition called focal segmental glomerulosclerosis (FSGS). This scarring is due to loss of podocytes, cells critical for glomerular filtration, and leads to proteinuria and kidney failure. Inherited forms of FSGS are caused by Rac1-activating mutations, and Rac1 induces TRPC5 ion channel activity and cytoskeletal remodeling in podocytes. Whether TRPC5 activity mediates FSGS onset and progression is unknown. We identified a small molecule, AC1903, that specifically blocks TRPC5 channel activity in glomeruli of proteinuric rats. Chronic administration of AC1903 suppressed severe proteinuria and prevented podocyte loss in a transgenic rat model of FSGS. AC1903 also provided therapeutic benefit in a rat model of hypertensive proteinuric kidney disease. These data indicate that TRPC5 activity drives disease and that TRPC5 inhibitors may be valuable for the treatment of progressive kidney diseases.




Structural basis for methylphosphonate biosynthesis

2017-12-07T10:23:19-08:00

Methylphosphonate synthase (MPnS) produces methylphosphonate, a metabolic precursor to methane in the upper ocean. Here, we determine a 2.35-angstrom resolution structure of MPnS and discover that it has an unusual 2-histidine-1-glutamine iron-coordinating triad. We further solve the structure of a related enzyme, hydroxyethylphosphonate dioxygenase from Streptomyces albus (SaHEPD), and find that it displays the same motif. SaHEPD can be converted into an MPnS by mutation of glutamine-adjacent residues, identifying the molecular requirements for methylphosphonate synthesis. Using these sequence markers, we find numerous putative MPnSs in marine microbiomes and confirm that MPnS is present in the abundant Pelagibacter ubique. The ubiquity of MPnS-containing microbes supports the proposal that methylphosphonate is a source of methane in the upper, aerobic ocean, where phosphorus-starved microbes catabolize methylphosphonate for its phosphorus.







New Products

2017-12-07T10:23:19-08:00










An unexpected career resource

2017-12-07T10:23:19-08:00




Comment on "Cognition-mediated evolution of low-quality floral nectars"

2017-12-07T10:23:19-08:00

Nachev et al. (Reports, 6 January 2017, p. 75) present dilute nectar in bat-pollinated plants as "paradoxical" because bats prefer concentrated nectar, but paradox disappears with realistic assumptions about nectar evolution. We argue that they make unrealistic assumptions about the cognitive abilities of bat pollinators, invoke Weber’s law inappropriately, and cannot predict observed nectar concentrations of bat flowers or negative correlations between pollinator body size and average concentration.




A generative vision model that trains with high data efficiency and breaks text-based CAPTCHAs

2017-12-07T10:23:19-08:00

Learning from a few examples and generalizing to markedly different situations are capabilities of human visual intelligence that are yet to be matched by leading machine learning models. By drawing inspiration from systems neuroscience, we introduce a probabilistic generative model for vision in which message-passing–based inference handles recognition, segmentation, and reasoning in a unified way. The model demonstrates excellent generalization and occlusion-reasoning capabilities and outperforms deep neural networks on a challenging scene text recognition benchmark while being 300-fold more data efficient. In addition, the model fundamentally breaks the defense of modern text-based CAPTCHAs (Completely Automated Public Turing test to tell Computers and Humans Apart) by generatively segmenting characters without CAPTCHA-specific heuristics. Our model emphasizes aspects such as data efficiency and compositionality that may be important in the path toward general artificial intelligence.




Response to Comment on "Cognition-mediated evolution of low-quality floral nectars"

2017-12-07T10:23:19-08:00

Pyke and Waser claim that our virtual pollination ecology model makes unrealistic assumptions and fails to predict observed nectar concentrations of bat flowers and negative correlations between pollinator body size and sugar concentration. In their comment, crucial model features are misrepresented, misunderstood, or ignored. Sensitivity to the supply/demand ratio explains both the equilibrium concentrations and the selection for lower concentrations by larger pollinators.







On the origin of modern humans: Asian perspectives

2017-12-07T10:23:19-08:00

The traditional "out of Africa" model, which posits a dispersal of modern Homo sapiens across Eurasia as a single wave at ~60,000 years ago and the subsequent replacement of all indigenous populations, is in need of revision. Recent discoveries from archaeology, hominin paleontology, geochronology, genetics, and paleoenvironmental studies have contributed to a better understanding of the Late Pleistocene record in Asia. Important findings highlighted here include growing evidence for multiple dispersals predating 60,000 years ago in regions such as southern and eastern Asia. Modern humans moving into Asia met Neandertals, Denisovans, mid-Pleistocene Homo, and possibly H. floresiensis, with some degree of interbreeding occurring. These early human dispersals, which left at least some genetic traces in modern populations, indicate that later replacements were not wholesale.