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Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

Making the paperTrevor Ireland Moon dust offers a fresh perspective on the origins of the Solar System. Abstractions Senior AuthorFish oil has a reputation as ?brain food?, but whether this is justified and, if so, how the oil works, is unclear. Working with his colleague Frédéric Darios, Bazbek Davletov at the MRC Laboratory of Molecular Biology in Cambridge, UK, was studying protein?protein QuantifiedSouth Africa A numerical perspective on Nature authors.Nigel Bennett at the University of Pretoria, South Africa, is part of an international collaboration that has been working hard to put Damaraland mole-rats (Cryptomys damarensis) on the map. Bennett takes his group on regular field Towards better biosecurity Slowly but surely, a key advisory committee is helping the scientific community act more responsibly when conducting and publishing biological research that could carry security risks. Shooting the messenger The abolition of a science advisory board to the US government sends the wrong signal. Rightful owners Research into anthropological artefacts must acknowledge claims of prior ownership. Research highlights Cancer biology: Tumour assassinsScience311, 1780?1784 (2006)Although targeted therapies hold great potential for curing cancer, they often miss the mark because of inefficient delivery to the tumour. To improve their aim, Christopher Contag and his colleagues at Stanford University School of Medicine, Further accusations rock Japanese RNA laboratory Suspicion of fraud hangs over pioneering RNA work. Doubts over evolution block funding by Canadian agency Study of ?intelligent design? refused funds. Korean science powerhouse sends Nobel laureate packing Clash of cultures means early return for physics prizewinner. Guinea experts cry foul on tribal exhibits A new exhibition of Melanesian artefacts raises questions about how the pieces ended up in a Californian art museum. Rex Dalton investigates. Energy secretary ditches science advisers Independent panel dismissed after nearly 30 years. Wellcome Trust fuelled bid to save British science treasure Private donors finance return of Hooke's manuscript. From the front lines As the H5N1 flu virus continues to sweep across the globe, researchers in some of the countries affected describe in their own words the political and scientific challenges that they face. Sidelines On the Record?Luckily criminals wear trainers. If they all wore Oxford brogues we would be in a very difficult position.?Nigel Allinson of the University of Sheffield describes a computerized system being developed in Britain to identify shoeprints at crime scenes.?This Pope has News in brief Fantasy reference list leads to the sackWhat's in a name? Hui Liu, assistant dean of the medical school at Tsinghua University in Beijing, got his job after submitting a résumé that cited, among other things, a paper by ?H. Liu? in the Journal of Cell biologyThe story of i Multicellular creatures can be battlegrounds for competing populations of cells. Claire Ainsworth learns how this way of looking at an individual is feeding into immunology and cancer biology. Climate scienceA sinking feeling The floods are getting worse in Tuvalu. As scientists argue over climate change and struggle to measure rising seas, Samir S. Patel meets the locals of this tiny island nation. Biologist aims to ease the pain for entrepreneurs Biotech start-ups face a struggle to survive. Virginia Gewin reports on an initiative that brings cash and experience together to improve their chances. In brief Totally wiredThe United States has reclaimed pole position in a league table of the ?most-wired? nations, according to the World Economic Forum. Singapore, Denmark, Iceland and Finland fleetingly supplanted it last year as the nations where telecommunications and information technology had the widest and Market watch Wood Mackenzie, an Edinburgh-based research and consulting firm, reviews recent trends in biotechnology stocks. The Nasdaq biotechnology index rose in February and dropped back in March, but the overall trend remains positive, with a gain of 6% since the start of the year. February Avoiding hazards of best-guess climate scenarios SirYour Special Report ?The costs of global warming? (Nature439, 374?375; 2006) gives an unbalanced picture of the emissions scenarios developed by the Intergovernmental Panel on Climate Change (IPCC).In contrast to the claim that these scenarios are Physician?scientists are needed now more than ever SirYour News Feature ?Them and us no longer? (Nature439, 779?780; 2006), about the narrowing divide between medical doctors and PhD scientists, ends with a disturbing assumption: that ?the era of the physician?scientist [is drawing] to a close?. India's concern about both security and sea research SirI share marine researchers' feelings about restrictions on carrying out research in Indian waters, as expressed in your News story ?India's ban on foreign boats hinders tsunami research? (Nature439, 380; 200610.1038/439380b). But few countries allow foreign vessels into Tools needed to navigate landscape of the genome SirI enjoyed your News Feature ?The web-wide world? (Nature439, 776?778; 2006), highlighting the impact of Google Earth on the scientific community. The success of this program underscores the importance of open standards for data and easy interoperation Feline friend or potential foe? What role do cats play in the epidemiology of H5N1 avian flu virus? We don't yet have all the answers, but it's time to consider new precautions, argue Thijs Kuiken, Albert Osterhaus, Peter Roeder and their colleagues. The making of geology In the late eighteenth century, ideas about the age of rocks and fossils gave rise to a new science. Men of astronomy As a youth, Ian Glass was inspired by Eric Temple Bell's book Men of Mathematics (Simon & Schuster, 1937), which profiled more than 30 mathematicians. In Revolutionaries of the Cosmos, Glass has attempted to do much the same for astronomy. He has restricted The puzzle of cooperation Robert May began his last presidential address to the Royal Society on 30 November 2005 by saying: ?The most important unanswered question in evolutionary biology, and more generally in the social sciences, is how cooperative behaviour evolved and can be maintained in human or other Back to the drawing board? Among the many services that Michael Faraday rendered to science was his innovation of illustrating theoretical ideas by means of pictures and diagrams. For Faraday, who knew next to no mathematics but had a powerful visual imagination, the image was the concept. But as his Science in culture: High impact From protons to galaxies, Cosmic Collisions shows us what happens when things go bump. PalaeontologyA firm step from water to land A project designed to discover fossils that illuminate the transition between fishes and land vertebrates has delivered the goods. At a stroke, our picture of that transition is greatly improved. EvolutionIt pays to laze Hidden beneath small mounds in the Kalahari Desert in southern Africa, Damaraland mole-rats (Cryptomys damarensis, pictured) have developed a remarkable caste system. In the life cycle of these animals, which is spent entirely underground, a single ?queen? female mates with one or two SemiconductorsSpray-on silicon Reports of the death of silicon electronics may well have been exaggerated. A technique that allows the deposition of silicon films from solution could harbinger the era of the inkjet-printed circuit. ImmunologyThe pick of the nibbled bits How does the immune system avoid potentially damaging responses against the body's own molecules? The answer lies partly in the ability of dendritic cells to sample their surroundings selectively. Solar systemWhen the dust unsettles Two attempts to measure the isotopic composition of oxygen in the Sun from particles trapped in lunar soils give very different results. A rethink of why the Solar System is as it is might be required. ArchaeologyFailure and how to avoid it Nothing lasts for ever, not least human civilizations. There are many reasons why societies stand or fall, and these lessons from the past require investigation at various places and on various timescales. Fluid dynamicsThe rough with the smooth Those who go with the flow assert that rough surfaces cause turbulence in fluids passing over them. The claim that, under certain conditions, the opposite is possible disturbs that cherished belief. PalaeontologyEarly Neolithic tradition of dentistry Flint tips were surprisingly effective for drilling tooth enamel in a prehistoric population.Prehistoric evidence for the drilling of human teeth in vivo has so far been limited to isolated cases from less than six millennia ago. Here we describe eleven drilled molar crowns from nine adults discovered in a Neolithic graveyard in Pakistan that dates from 7,500?9,000 years ago. These findings provide evidence for a long tradition of a type of proto-dentistry in an early farming culture. ParasitologyParasite survives predation on its host As prisoners in their living habitat, parasites should be vulnerable to destruction by the predators of their hosts. But we show here that the parasitic gordian worm Paragordius tricuspidatus is able to escape not only from its insect host after ingestion by a fish or frog but also from the digestive tract of the predator. This remarkable tactic enables the worm to continue its life cycle. Animal behaviourChimpanzee choice and prosociality Arising from: J. B. Silk et al. Nature437, 1357?1359 (2005); Silk et al. replySilk et al. report that adult chimpanzees show no difference in their choices in a situation where one choice benefits a familiar conspecific and the other does not. From this, they conclude that chimpanzees are indifferent to the welfare of unrelated group members. But without additional data confirming that chimpanzees do choose differently in circumstances in which a difference would be expected, the authors cannot conclude that there is no difference in their scenario. How chimpanzees react to the welfare of unrelated group members remains an open question. Animal behaviourChimpanzee choice and prosociality (Reply) Beninger and Quinsey argue that we provide no evidence that chimpanzees show other-regarding preferences in the two-option test situation under conditions in which they would be expected to show such a preference. This criticism is misdirected, because our aim was not to determine whether chimpanzees would demonstrate prosocial preference under any circumstances. Instead, it was to determine whether chimpanzees show pro-social preferences in situations similar to those in which these occur routinely in humans. A Devonian tetrapod-like fish and the evolution of the tetrapod body plan The relationship of limbed vertebrates (tetrapods) to lobe-finned fish (sarcopterygians) is well established, but the origin of major tetrapod features has remained obscure for lack of fossils that document the sequence of evolutionary changes. Here we report the discovery of a well-preserved species of fossil The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb Wrists, ankles and digits distinguish tetrapod limbs from fins, but direct evidence on the origin of these features has been unavailable. Here we describe the pectoral appendage of a member of the sister group of tetrapods, Tiktaalik roseae, which is morphologically and functionally transitional A debris disk around an isolated young neutron star Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such ?fallback? is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of the order of 10 Earth masses, and its lifetime (? 106?years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars. Isotopic enhancements of 17O and 18O from solar wind particles in the lunar regolith Differences in isotopic abundances between meteorites and rocks on Earth leave unclear the true composition of the gas out of which the Solar System formed. The Sun should have preserved in its outer layers the original composition, and recent work has indicated that the solar wind is enriched in 16O, relative to Earth, Mars and bulk meteorites. This suggests that self-shielding of CO due to photo-dissociation, which is a well understood process in molecular clouds, also led to evolution in the isotopic abundances in the early Solar System. Here we report measurements of oxygen isotopic abundances in lunar grains that were recently exposed to the solar wind. We find that 16O is underabundant, opposite to an earlier finding based on studies of ancient metal grains. Our result, however, is more difficult to understand within the context of current models, because there is no clear way to make 16O more abundant in Solar System rocks than in the Sun. Quantum interference between two single photons emitted by independently trapped atoms When two indistinguishable single photons are fed into the two input ports of a beam splitter, the photons will coalesce and leave together from the same output port. This is a quantum interference effect, which occurs because two possible paths?in which the photons leave by different output ports?interfere destructively. This effect was first observed in parametric downconversion (in which a nonlinear crystal splits a single photon into two photons of lower energy), then from two separate downconversion crystals, as well as with single photons produced one after the other by the same quantum emitter. With the recent developments in quantum information research, much attention has been devoted to this interference effect as a resource for quantum data processing using linear optics techniques. To ensure the scalability of schemes based on these ideas, it is crucial that indistinguishable photons are emitted by a collection of synchronized, but otherwise independent sources. Here we demonstrate the quantum interference of two single photons emitted by two independently trapped single atoms, bridging the gap towards the simultaneous emission of many indistinguishable single photons by different emitters. Our data analysis shows that the observed coalescence is mainly limited by wavefront matching of the light emitted by the two atoms, and to a lesser extent by the motion of each atom in its own trap. Solution-processed silicon films and transistors The use of solution processes?as opposed to conventional vacuum processes and vapour-phase deposition?for the fabrication of electronic devices has received considerable attention for a wide range of applications, with a view to reducing processing costs. In particular, the ability to print semiconductor devices using liquid-phase materials could prove essential for some envisaged applications, such as large-area flexible displays. Recent research in this area has largely been focused on organic semiconductors, some of which have mobilities comparable to that of amorphous silicon (a-Si); but issues of reliability remain. Solution processing of metal chalcogenide semiconductors to fabricate stable and high-performance transistors has also been reported. This class of materials is being explored as a possible substitute for silicon, given the complex and expensive manufacturing processes required to fabricate devices from the latter. However, if high-quality silicon films could be prepared by a solution process, this situation might change drastically. Here we demonstrate the solution processing of silicon thin-film transistors (TFTs) using a silane-based liquid precursor. Using this precursor, we have prepared polycrystalline silicon (poly-Si) films by both spin-coating and ink-jet printing, from which we fabricate TFTs with mobilities of 108?cm2?V-1?s-1 and 6.5?cm2?V-1?s-1, respectively. Although the processing conditions have yet to be optimized, these mobilities are already greater than those that have been achieved in solution-processed organic TFTs, and they exceed those of a-Si TFTs (? 1?cm2?V-1?s-1). Increased Arctic cloud longwave emissivity associated with pollution from mid-latitudes There is consensus among climate models that Arctic climate is particularly sensitive to anthropogenic greenhouse gases and that, over the next century, Arctic surface temperatures are projected to rise at a rate about twice the global mean. The response of Arctic surface temperatures to greenhouse gas thermal emission is modified by Northern Hemisphere synoptic meteorology and local radiative processes. Aerosols may play a contributing factor through changes to cloud radiative properties. Here we evaluate a previously suggested contribution of anthropogenic aerosols to cloud emission and surface temperatures in the Arctic. Using four years of ground-based aerosol and radiation measurements obtained near Barrow, Alaska, we show that, where thin water clouds and pollution are coincident, there is an increase in cloud longwave emissivity resulting from elevated haze levels. This results in an estimated surface warming under cloudy skies of between 3.3 and 5.2?W?m-2 or 1 and 1.6?°C. Arctic climate is closely tied to cloud longwave emission, but feedback mechanisms in the system are complex and the actual climate response to the described sensitivity remains to be evaluated. Deciphering the evolution and metabolism of an anammox bacterium from a community genome Anaerobic ammonium oxidation (anammox) has become a main focus in oceanography and wastewater treatment. It is also the nitrogen cycle's major remaining biochemical enigma. Among its features, the occurrence of hydrazine as a free intermediate of catabolism, the biosynthesis of ladderane lipids and the role of cytoplasm differentiation are unique in biology. Here we use environmental genomics?the reconstruction of genomic data directly from the environment?to assemble the genome of the uncultured anammox bacterium Kuenenia stuttgartiensis from a complex bioreactor community. The genome data illuminate the evolutionary history of the Planctomycetes and allow us to expose the genetic blueprint of the organism's special properties. Most significantly, we identified candidate genes responsible for ladderane biosynthesis and biological hydrazine metabolism, and discovered unexpected metabolic versatility. Energetics reveals physiologically distinct castes in a eusocial mammal Eusociality, which occurs among mammals only in two species of African mole-rat, is characterized by division of labour between morphologically distinct ?castes?. In Damaraland mole-rats (Cryptomys damarensis), colony labour is divided between ?infrequent worker? and ?frequent worker? castes. Frequent workers are active year-round and together perform more than 95% of the total work of the colony, whereas infrequent workers typically perform less than 5% of the total work. Anecdotal evidence suggests that infrequent workers may act as dispersers, with dispersal being limited to comparatively rare periods when the soil is softened by moisture. Here we show that infrequent workers and queens increase their daily energy expenditure after rainfall whereas frequent workers do not. Infrequent workers are also fatter than frequent workers. We suggest that infrequent workers constitute a physiologically distinct dispersing caste, the members of which, instead of contributing to the work of the colony and helping the queen to reproduce, build up their own body reserves in preparation for dispersal and reproduction when environmental conditions are suitable. An unconventional myosin in Drosophila reverses the default handedness in visceral organs The internal organs of animals often have left?right asymmetry. Although the formation of the anterior?posterior and dorsal?ventral axes in Drosophila is well understood, left?right asymmetry has not been extensively studied. Here we find that the handedness of the embryonic gut and the adult gut and testes is reversed (not randomized) in viable and fertile homozygous Myo31DF mutants. Myo31DF encodes an unconventional myosin, Drosophila MyoIA (also referred to as MyoID in mammals; refs 3, 4), and is the first actin-based motor protein to be implicated in left?right patterning. We find that Myo31DF is required in the hindgut epithelium for normal embryonic handedness. Disruption of actin filaments in the hindgut epithelium randomizes the handedness of the embryonic gut, suggesting that Myo31DF function requires the actin cytoskeleton. Consistent with this, we find that Myo31DF colocalizes with the cytoskeleton. Overexpression of Myo61F, another myosin I (ref. 4), reverses the handedness of the embryonic gut, and its knockdown also causes a left?right patterning defect. These two unconventional myosin I proteins may have antagonistic functions in left?right patterning. We suggest that the actin cytoskeleton and myosin I proteins may be crucial for generating left?right asymmetry in invertebrates. Type ID unconventional myosin controls left?right asymmetry in Drosophila Breaking left?right symmetry in Bilateria embryos is a major event in body plan organization that leads to polarized adult morphology, directional organ looping, and heart and brain function. However, the molecular nature of the determinant(s) responsible for the invariant orientation of the left?right axis (situs choice) remains largely unknown. Mutations producing a complete reversal of left?right asymmetry (situs inversus) are instrumental for identifying mechanisms controlling handedness, yet only one such mutation has been found in mice (inversin) and snails. Here we identify the conserved type ID unconventional myosin 31DF gene (Myo31DF) as a unique situs inversus locus in Drosophila. Myo31DF mutations reverse the dextral looping of genitalia, a prominent left?right marker in adult flies. Genetic mosaic analysis pinpoints the A8 segment of the genital disc as a left?right organizer and reveals an anterior?posterior compartmentalization of Myo31DF function that directs dextral development and represses a sinistral default state. As expected of a determinant, Myo31DF has a trigger-like function and is expressed symmetrically in the organizer, and its symmetrical overexpression does not impair left?right asymmetry. Thus Myo31DF is a dextral gene with actin-based motor activity controlling situs choice. Like mouse inversin, Myo31DF interacts and colocalizes with ?-catenin, suggesting that situs inversus genes can direct left?right development through the adherens junction. Toll-dependent selection of microbial antigens for presentation by dendritic cells Dendritic cells constitutively sample the tissue microenvironment and phagocytose both microbial and host apoptotic cells. This leads to the induction of immunity against invading pathogens or tolerance to peripheral self antigens, respectively. The outcome of antigen presentation by dendritic cells depends on their activation status, such that Toll-like receptor (TLR)-induced dendritic cell activation makes them immunogenic, whereas steady-state presentation of self antigens leads to tolerance. TLR-inducible expression of co-stimulatory signals is one of the mechanisms of self/non-self discrimination. However, it is unclear whether or how the inducible expression of co-stimulatory signals would distinguish between self antigens and microbial antigens when both are encountered by dendritic cells during infection. Here we describe a new mechanism of antigen selection in dendritic cells for presentation by major histocompatibility complex class II molecules (MHC?II) that is based on the origin of the antigen. We show that the efficiency of presenting antigens from phagocytosed cargo is dependent on the presence of TLR ligands within the cargo. Furthermore, we show that the generation of peptide?MHC class II complexes is controlled by TLRs in a strictly phagosome-autonomous manner. Omega-3 and omega-6 fatty acids stimulate cell membrane expansion by acting on syntaxin?3 Growth of neurite processes from the cell body is the critical step in neuronal development and involves a large increase in cell membrane surface area. Arachidonic-acid-releasing phospholipases are highly enriched in nerve growth cones and have previously been implicated in neurite outgrowth. Cell membrane expansion is achieved through the fusion of transport organelles with the plasma membrane; however, the identity of the molecular target of arachidonic acid has remained elusive. Here we show that syntaxin?3 (STX3), a plasma membrane protein, has an important role in the growth of neurites, and also serves as a direct target for omega-6 arachidonic acid. By using syntaxin?3 in a screening assay, we determined that the dietary omega-3 linolenic and docosahexaenoic acids can efficiently substitute for arachidonic acid in activating syntaxin?3. Our findings provide a molecular basis for the previously established action of omega-3 and omega-6 polyunsaturated fatty acids in membrane expansion at the growth cones, and represent the first identification of a single effector molecule for these essential nutrients. Nck adaptor proteins link nephrin to the actin cytoskeleton of kidney podocytes The glomerular filtration barrier in the kidney is formed in part by a specialized intercellular junction known as the slit diaphragm, which connects adjacent actin-based foot processes of kidney epithelial cells (podocytes). Mutations affecting a number of slit diaphragm proteins, including nephrin (encoded by NPHS1), lead to renal disease owing to disruption of the filtration barrier and rearrangement of the actin cytoskeleton, although the molecular basis for this is unclear. Here we show that nephrin selectively binds the Src homology 2 (SH2)/SH3 domain-containing Nck adaptor proteins, which in turn control the podocyte cytoskeleton in vivo. The cytoplasmic tail of nephrin has multiple YDxV sites that form preferred binding motifs for the Nck SH2 domain once phosphorylated by Src-family kinases. We show that this Nck?nephrin interaction is required for nephrin-dependent actin reorganization. Selective deletion of Nck from podocytes of transgenic mice results in defects in the formation of foot processes and in congenital nephrotic syndrome. Together, these findings identify a physiological signalling pathway in which nephrin is linked through phosphotyrosine-based interactions to Nck adaptors, and thus to the underlying actin cytoskeleton in podocytes. Simple and widely expressed SH2/SH3 adaptor proteins can therefore direct the formation of a specialized cellular morphology in vivo. Semi-conservative DNA replication through telomeres requires Taz1 Telomere replication is achieved through the combined action of the conventional DNA replication machinery and the reverse transcriptase, telomerase. Telomere-binding proteins have crucial roles in controlling telomerase activity; however, little is known about their role in controlling semi-conservative replication, which synthesizes the bulk of telomeric DNA. Telomere repeats in the fission yeast Schizosaccharomyces pombe are bound by Taz1, a regulator of diverse telomere functions. It is generally assumed that telomere-binding proteins impede replication fork progression. Here we show that, on the contrary, Taz1 is crucial for efficient replication fork progression through the telomere. Using two-dimensional gel electrophoresis, we find that loss of Taz1 leads to stalled replication forks at telomeres and internally placed telomere sequences, regardless of whether the telomeric G-rich strand is replicated by leading- or lagging-strand synthesis. In contrast, the Taz1-interacting protein Rap1 is dispensable for efficient telomeric fork progression. Upon loss of telomerase, taz1? telomeres are lost precipitously, suggesting that maintenance of taz1? telomere repeats cannot be sustained through semi-conservative replication. As the human telomere proteins TRF1 and TRF2 are Taz1 orthologues, we predict that one or both of the human TRFs may orchestrate fork passage through human telomeres. Stalled forks at dysfunctional human telomeres are likely to accelerate the genomic instability that drives tumorigenesis. Proton-coupled electron transfer drives the proton pump of cytochrome c oxidase Electron transfer in cell respiration is coupled to proton translocation across mitochondrial and bacterial membranes, which is a primary event of biological energy transduction. The resulting electrochemical proton gradient is used to power energy-requiring reactions, such as ATP synthesis. Cytochrome c oxidase is a key component of the respiratory chain, which harnesses dioxygen as a sink for electrons and links O2 reduction to proton pumping. Electrons from cytochrome c are transferred sequentially to the O2 reduction site of cytochrome c oxidase via two other metal centres, CuA and haem a, and this is coupled to vectorial proton transfer across the membrane by a hitherto unknown mechanism. On the basis of the kinetics of proton uptake and release on the two aqueous sides of the membrane, it was recently suggested that proton pumping by cytochrome c oxidase is not mechanistically coupled to internal electron transfer. Here we have monitored translocation of electrical charge equivalents as well as electron transfer within cytochrome c oxidase in real time. The results show that electron transfer from haem a to the O2 reduction site initiates the proton pump mechanism by being kinetically linked to an internal vectorial proton transfer. This reaction drives the proton pump and occurs before relaxation steps in which protons are taken up from the aqueous space on one side of the membrane and released on the other. Crystal structure of the CorA Mg2+ transporter The magnesium ion, Mg2+, is essential for myriad biochemical processes and remains the only major biological ion whose transport mechanisms remain unknown. The CorA family of magnesium transporters is the primary Mg2+ uptake system of most prokaryotes and a functional homologue of the eukaryotic mitochondrial magnesium transporter. Here we determine crystal structures of the full-length Thermotoga maritima CorA in an apparent closed state and its isolated cytoplasmic domain at 3.9?Å and 1.85?Å resolution, respectively. The transporter is a funnel-shaped homopentamer with two transmembrane helices per monomer. The channel is formed by an inner group of five helices and putatively gated by bulky hydrophobic residues. The large cytoplasmic domain forms a funnel whose wide mouth points into the cell and whose walls are formed by five long helices that are extensions of the transmembrane helices. The cytoplasmic neck of the pore is surrounded, on the outside of the funnel, by a ring of highly conserved positively charged residues. Two negatively charged helices in the cytoplasmic domain extend back towards the membrane on the outside of the funnel and abut the ring of positive charge. An apparent Mg2+ ion was bound between monomers at a conserved site in the cytoplasmic domain, suggesting a mechanism to link gating of the pore to the intracellular concentration of Mg2+. My morning glory What a way to start the day.