Editorials
患者の医療記録をデータベースに一元化する英国の計画は、有益で研究にも役立つと高く評価できるが、患者の拒否権が軽視されている。
Power to the people p.261
A planned database collating medical information for England’s population is a laudable exercise, with huge potential for research. But people’s right to opt out has been greatly downplayed.
doi: 10.1038/505261a
寒波が猛威を振るっているが、これは地球温暖化が弱まっていることを意味しているわけでなく、地球温暖化への取り組みを忘れてはならない。
Cool heads needed p.261
As cold weather rages, it is easy to forget the difference between weather and climate.
doi: 10.1038/505261b
渡り鳥がV字形の隊列を作って飛ぶ利点が、絶滅危惧種ホオアカトキの飛翔調査によって明らかになった。
V is for vortex p.262
An endangered species helps scientists to learn why migrating birds fly in a familiar formation.
doi: 10.1038/505262a
News
冬眠モードに入っていたESA（欧州宇宙機関）の彗星探査機ロゼッタの、目覚めが間近に。
Comet craft ready to wake p.269
Stakes high as European Space Agency waits for Rosetta orbiter to come out of hibernation.
doi: 10.1038/505269a
南極で立ち往生した民間の科学調査船がようやく救出されたが、この調査には批判も。
Researchers question rescued polar expedition p.270
Australian Antarctic Division says it did not approve research strategy of stricken mission.
doi: 10.1038/505270a
バイオリポジトリが着実に活用されているが、資金問題に直面するところも。
Repositories share key research tools p.272
But some biological resource centres face funding issues.
doi: 10.1038/505272a
電流の単位アンペアの定義を見直そうとの動きが。
Ampere to get rational redefinition p.273
Single-electron flow measured in bid to overhaul SI base unit.
doi: 10.1038/505273a
NASAのケプラー宇宙望遠鏡のデータが、Ia型超新星の起源の見直しの手がかりに。
Kepler clue to supernova puzzle p.274
Two white dwarfs favoured as precursors of type Ia supernovae.
doi: 10.1038/505274a
News Features
気候変動：失われた熱の実態
Climate change: The case of the missing heat p.276
科学者たちを悩ませてきた16年間にわたる「地球温暖化の中断」の原因についての手がかりが、徐々に集まりつつある。
doi: 10.1038/505276a
天体物理学：暗黒の中心
Astrophysics: The heart of darkness p.280
大きな星雲の中心に必ず存在する超大質量ブラックホールの謎が、次第に明らかになりつつある。
doi: 10.1038/505280a
News & Views
地球科学：河川下刻を再考する
Earth science: River incision revisited p.294
河川による岩盤浸食のデータセットをまとめた結果から、その測定結果は観測の時間スケールに依存しており、段丘などの下刻地形が気候とテクトニクスの変化を忠実に記録しているかどうかが疑わしくなってきた。
doi: 10.1038/505294a
鳥類の飛翔：仲間の羽ばたきに助けられながら飛ぶ
Bird flight: Fly with a little flap from your friends p.295
V字型の編隊を作って飛ぶホオアカトキについて空中で計測を行った結果、この鳥は仲間との相対的な位置を調節し、羽ばたきを同調させることで、エネルギーを節約しているという仮説に一致する飛行をしていることが明らかになった。
doi: 10.1038/505295a
宇宙物理学：高速回転する星を周回するブラックホール
Astrophysics: Black hole found orbiting a fast rotator p.296
放射スペクトルから「Be」型とされる恒星は中性子星、または中性子星に似た進化した星を伴うことが多いが、ブラックホールを伴うBe型星はこれまで見つかっていなかった。だが、あるブラックホールの正体が、その周囲からの可視光放射によって明かされることになった。
doi: 10.1038/505296a
植物科学：「妖精の輪」を作る化学物質
Plant science: Fairy chemicals p.298
キノコが地面に輪状に生えてくる菌輪、あるいはフェアリーリング（妖精の輪）と呼ばれる現象に関連した成長促進物質が、真菌の1種から4年前に単離された。そして今回、植物もこの促進物質を産生・代謝していることが明らかになった。
doi: 10.1038/505298a
分子生物学：DNA修復 – 押してもだめなら引いてみよう
Molecular biology: The tug of DNA repair p.298
転写酵素であるRNAポリメラーゼはDNAの損傷があるとそこで立ち往生してしまい、損傷修復を妨げる。補助因子がこの酵素を前方に押してそこから追い出すのだが、後ろ向きに引っ張ってもおそらく効果は同じらしいことが分かった。
doi: 10.1038/nature12850
Articles
神経科学：自閉症や統合失調症のリスク因子であるCNVは対照群の認知機能に影響を与える
CNVs conferring risk of autism or schizophrenia affect cognition in controls p.361
Rare copy-number variants (CNVs) conferring risk of schizophrenia or autism affect fecundity of carriers in Iceland, and carriers of these CNVs who do not suffer disease or have not been diagnosed with intellectual disability show phenotypes in brain structure and cognitive abilities between those of non-carrier controls and patients with schizophrenia.
doi: 10.1038/nature12818
細胞生物学：コヒーシンリングによるトポロジカルなDNA結合の生化学的再構成
Biochemical reconstitution of topological DNA binding by the cohesin ring p.367
Many DNA processes require chromosomes to be held together by a ring-shaped complex called cohesin, but despite the importance of this protein, its interaction with DNA has not been reproduced in vitro; here, using purified yeast proteins, cohesin loading is successfully recapitulated, offering mechanistic insight into how the loader complex mediates topological cohesin binding.
doi: 10.1038/nature12867
分子生物学：UvrDはRNAポリメラーゼを後退させることでDNA修復を助ける
UvrD facilitates DNA repair by pulling RNA polymerase backwards p.372
UvrD acts in nucleotide excision repair by using its helicase/translocase activity to induce RNA polymerase backtracking, enabling repair enzymes to access DNA lesions.
doi: 10.1038/nature12928
Letters
宇宙：ブラックホール伴星を持つBe型星
A Be-type star with a black-hole companion p.378
Stellar-mass black holes have all been discovered through X-ray emission, which arises from the accretion of gas from their binary companions (this gas is either stripped from low-mass stars or supplied as winds from massive ones). Binary evolution models also predict the existence of black holes accreting from the equatorial envelope of rapidly spinning Be-type stars (stars of the Be type are hot blue irregular variables showing characteristic spectral emission lines of hydrogen). Of the approximately 80 Be X-ray binaries known in the Galaxy, however, only pulsating neutron stars have been found as companions. A black hole was formally allowed as a solution for the companion to the Be star MWC 656 (ref. 5; also known as HD 215227), although that conclusion was based on a single radial velocity curve of the Be star, a mistaken spectral classification and rough estimates of the inclination angle. Here we report observations of an accretion disk line mirroring the orbit of MWC 656. This, together with an improved radial velocity curve of the Be star through fitting sharp Fe ii profiles from the equatorial disk, and a refined Be classification (to that of a B1.5–B2 III star), indicates that a black hole of 3.8 to 6.9 solar masses orbits MWC 656, the candidate counterpart of the γ-ray source AGL J2241+4454 (refs 5, 6). The black hole is X-ray quiescent and fed by a radiatively inefficient accretion flow giving a luminosity less than 1.6 × 10−7 times the Eddington luminosity. This implies that Be binaries with black-hole companions are difficult to detect in conventional X-ray surveys.
doi: 10.1038/nature12916
材料科学：ナノ粒子溶液をゲルや生物組織の接着剤に
Nanoparticle solutions as adhesives for gels and biological tissues p.382
Adhesives are made of polymers because, unlike other materials, polymers ensure good contact between surfaces by covering asperities, and retard the fracture of adhesive joints by dissipating energy under stress. But using polymers to ‘glue’ together polymer gels is difficult, requiring chemical reactions, heating, pH changes, ultraviolet irradiation or an electric field. Here we show that strong, rapid adhesion between two hydrogels can be achieved at room temperature by spreading a droplet of a nanoparticle solution on one gel’s surface and then bringing the other gel into contact with it. The method relies on the nanoparticles’ ability to adsorb onto polymer gels and to act as connectors between polymer chains, and on the ability of polymer chains to reorganize and dissipate energy under stress when adsorbed onto nanoparticles. We demonstrate this approach by pressing together pieces of hydrogels, for approximately 30 seconds, that have the same or different chemical properties or rigidities, using various solutions of silica nanoparticles, to achieve a strong bond. Furthermore, we show that carbon nanotubes and cellulose nanocrystals that do not bond hydrogels together become adhesive when their surface chemistry is modified. To illustrate the promise of the method for biological tissues, we also glued together two cut pieces of calf’s liver using a solution of silica nanoparticles. As a rapid, simple and efficient way to assemble gels or tissues, this method is desirable for many emerging technological and medical applications such as microfluidics, actuation, tissue engineering and surgery.
doi: 10.1038/nature12806
化学：二ホウ素化とクロスカップリングのカスケードによる末端アルケンからの不斉合成
Asymmetric synthesis from terminal alkenes by cascades of diboration and cross-coupling p.386
Terminal, monosubstituted alkenes are ideal prospective starting materials for organic synthesis because they are manufactured on very large scales and can be functionalized via a broad range of chemical transformations. Alkenes also have the attractive feature of being stable in the presence of many acids, bases, oxidants and reductants. In spite of these attributes, relatively few catalytic enantioselective transformations have been developed that transform aliphatic α-olefins into chiral products with an enantiomeric excess greater then 90 per cent. With the exception of site-controlled isotactic polymerization of α-olefins, none of these catalytic enantioselective processes results in chain-extending carbon–carbon bond formation to the terminal carbon. Here we describe a strategy that directly addresses this gap in synthetic methodology, and present a single-flask, catalytic enantioselective conversion of terminal alkenes into a number of chiral products. These reactions are facilitated by a neighbouring functional group that accelerates palladium-catalysed cross-coupling of 1,2-bis(boronates) relative to non-functionalized alkyl boronate analogues. In tandem with enantioselective diboration, this reactivity feature transforms alkene starting materials into a diverse array of chiral products. We note that the tandem diboration/cross-coupling reaction generally provides products in high yield and high selectivity (>95:5 enantiomer ratio), uses low loadings (1–2 mol per cent) of commercially available catalysts and reagents, offers an expansive substrate scope, and can address a broad range of alcohol and amine synthesis targets, many of which cannot be easily addressed with current technology.
doi: 10.1038/nature12781
地球：104～107年の時間スケールにわたる基盤岩への河川下刻速度変化の特徴
A signature of transience in bedrock river incision rates over timescales of 104–107 years p.391
Measured rates of river incision into bedrock are commonly interpreted as proxies for rates of rock uplift (see refs 1 and 2, for example) and indices of the strength of climatic forcing of erosion over time (see refs 3 and 4, for example). This approach implicitly assumes that river incision rates are in equilibrium with external forcings over a wide range of timescales. Here we directly test this assumption by examining the temporal scaling of bedrock river incision from 155 independent measurements of river incision compiled from 14 sites. Of these sites, 11 exhibit a negative power-law dependence of bedrock river incision rate on measurement interval, a relationship that is apparent over timescales of 104–107 years and is independent of tectonic and geomorphic setting. Thus, like rates of sediment accumulation, rates of river incision into bedrock exhibit non-steady-state behaviour even over very long measurement intervals. Non-steady-state behaviour can be explained by episodic hiatuses in river incision triggered by alluvial deposition, if such hiatuses have a heavy-tailed length distribution. Regardless of its cause, the dependence of incision rate on measurement interval complicates efforts to infer tectonic or climatic forcing from changes in rates of river incision over time or from comparison of rates computed over different timescales.
doi: 10.1038/nature12913
生態学：湿地により促進されるアマゾン川からの二酸化炭素の放出
Amazon River carbon dioxide outgassing fuelled by wetlands p.395
River systems connect the terrestrial biosphere, the atmosphere and the ocean in the global carbon cycle. A recent estimate suggests that up to 3 petagrams of carbon per year could be emitted as carbon dioxide (CO2) from global inland waters, offsetting the carbon uptake by terrestrial ecosystems. It is generally assumed that inland waters emit carbon that has been previously fixed upstream by land plant photosynthesis, then transferred to soils, and subsequently transported downstream in run-off. But at the scale of entire drainage basins, the lateral carbon fluxes carried by small rivers upstream do not account for all of the CO2 emitted from inundated areas downstream. Three-quarters of the world’s flooded land consists of temporary wetlands, but the contribution of these productive ecosystems to the inland water carbon budget has been largely overlooked. Here we show that wetlands pump large amounts of atmospheric CO2 into river waters in the floodplains of the central Amazon. Flooded forests and floating vegetation export large amounts of carbon to river waters and the dissolved CO2 can be transported dozens to hundreds of kilometres downstream before being emitted. We estimate that Amazonian wetlands export half of their gross primary production to river waters as dissolved CO2 and organic carbon, compared with only a few per cent of gross primary production exported in upland (not flooded) ecosystems. Moreover, we suggest that wetland carbon export is potentially large enough to account for at least the 0.21 petagrams of carbon emitted per year as CO2 from the central Amazon River and its floodplains. Global carbon budgets should explicitly address temporary or vegetated flooded areas, because these ecosystems combine high aerial primary production with large, fast carbon export, potentially supporting a substantial fraction of CO2 evasion from inland waters.
doi: 10.1038/nature12797
鳥類の飛翔：トキ類の編隊飛行時に見られる、羽ばたきの位相制御による吹き上げ気流の利用と吹き下ろし気流の回避
Upwash exploitation and downwash avoidance by flap phasing in ibis formation flight p.399
Many species travel in highly organized groups. The most quoted function of these configurations is to reduce energy expenditure and enhance locomotor performance of individuals in the assemblage. The distinctive V formation of bird flocks has long intrigued researchers and continues to attract both scientific and popular attention. The well-held belief is that such aggregations give an energetic benefit for those birds that are flying behind and to one side of another bird through using the regions of upwash generated by the wings of the preceding bird, although a definitive account of the aerodynamic implications of these formations has remained elusive. Here we show that individuals of northern bald ibises (Geronticus eremita) flying in a V flock position themselves in aerodynamically optimum positions, in that they agree with theoretical aerodynamic predictions. Furthermore, we demonstrate that birds show wingtip path coherence when flying in V positions, flapping spatially in phase and thus enabling upwash capture to be maximized throughout the entire flap cycle. In contrast, when birds fly immediately behind another bird—in a streamwise position—there is no wingtip path coherence; the wing-beats are in spatial anti-phase. This could potentially reduce the adverse effects of downwash for the following bird. These aerodynamic accomplishments were previously not thought possible for birds because of the complex flight dynamics and sensory feedback that would be required to perform such a feat. We conclude that the intricate mechanisms involved in V formation flight indicate awareness of the spatial wake structures of nearby flock-mates, and remarkable ability either to sense or predict it. We suggest that birds in V formation have phasing strategies to cope with the dynamic wakes produced by flapping wings.
doi: 10.1038/nature12939
進化：シマ・デ・ロス・ウエソスで発掘されたヒト族のミトコンドリアゲノム塩基配列
A mitochondrial genome sequence of a hominin from Sima de los Huesos p.403
Excavations of a complex of caves in the Sierra de Atapuerca in northern Spain have unearthed hominin fossils that range in age from the early Pleistocene to the Holocene. One of these sites, the ‘Sima de los Huesos’ (‘pit of bones’), has yielded the world’s largest assemblage of Middle Pleistocene hominin fossils, consisting of at least 28 individuals dated to over 300,000 years ago. The skeletal remains share a number of morphological features with fossils classified as Homo heidelbergensis and also display distinct Neanderthal-derived traits. Here we determine an almost complete mitochondrial genome sequence of a hominin from Sima de los Huesos and show that it is closely related to the lineage leading to mitochondrial genomes of Denisovans, an eastern Eurasian sister group to Neanderthals. Our results pave the way for DNA research on hominins from the Middle Pleistocene.
doi: 10.1038/nature12788
神経科学：生後臨界期における異常な神経活動は大脳の血管形成を阻害する
Perturbed neural activity disrupts cerebral angiogenesis during a postnatal critical period p.407
During the neonatal period, activity-dependent neural-circuit remodelling coincides with growth and refinement of the cerebral microvasculature. Whether neural activity also influences the patterning of the vascular bed is not known. Here we show in neonatal mice, that neither reduction of sensory input through whisker trimming nor moderately increased activity by environmental enrichment affects cortical microvascular development. Unexpectedly, chronic stimulation by repetitive sounds, whisker deflection or motor activity led to a near arrest of angiogenesis in barrel, auditory and motor cortices, respectively. Chemically induced seizures also caused robust reductions in microvascular density. However, altering neural activity in adult mice did not affect the vasculature. Histological analysis and time-lapse in vivo two-photon microscopy revealed that hyperactivity did not lead to cell death or pruning of existing vessels but rather to reduced endothelial proliferation and vessel sprouting. This anti-angiogenic effect was prevented by administration of the nitric oxide synthase (NOS) inhibitor L-NAME and in mice with neuronal and inducible NOS deficiency, suggesting that excessive nitric oxide released from hyperactive interneurons and glia inhibited vessel growth. Vascular deficits persisted long after cessation of hyperstimulation, providing evidence for a critical period after which proper microvascular patterning cannot be re-established. Reduced microvascular density diminished the ability of the brain to compensate for hypoxic challenges, leading to dendritic spine loss in regions distant from capillaries. Therefore, excessive sensorimotor stimulation and repetitive neural activation during early childhood may cause lifelong deficits in microvascular reserve, which could have important consequences for brain development, function and pathology.
doi: 10.1038/nature12821
免疫：Muc5bは気道の防御に必要である
Muc5b is required for airway defence p.412
Respiratory surfaces are exposed to billions of particulates and pathogens daily. A protective mucus barrier traps and eliminates them through mucociliary clearance (MCC). However, excessive mucus contributes to transient respiratory infections and to the pathogenesis of numerous respiratory diseases. MUC5AC and MUC5B are evolutionarily conserved genes that encode structurally related mucin glycoproteins, the principal macromolecules in airway mucus. Genetic variants are linked to diverse lung diseases, but specific roles for MUC5AC and MUC5B in MCC, and the lasting effects of their inhibition, are unknown. Here we show that mouse Muc5b (but not Muc5ac) is required for MCC, for controlling infections in the airways and middle ear, and for maintaining immune homeostasis in mouse lungs, whereas Muc5ac is dispensable. Muc5b deficiency caused materials to accumulate in upper and lower airways. This defect led to chronic infection by multiple bacterial species, including Staphylococcus aureus, and to inflammation that failed to resolve normally. Apoptotic macrophages accumulated, phagocytosis was impaired, and interleukin-23 (IL-23) production was reduced in Muc5b−/− mice. By contrast, in mice that transgenically overexpress Muc5b, macrophage functions improved. Existing dogma defines mucous phenotypes in asthma and chronic obstructive pulmonary disease (COPD) as driven by increased MUC5AC, with MUC5B levels either unaffected or increased in expectorated sputum. However, in many patients, MUC5B production at airway surfaces decreases by as much as 90%. By distinguishing a specific role for Muc5b in MCC, and by determining its impact on bacterial infections and inflammation in mice, our results provide a refined framework for designing targeted therapies to control mucin secretion and restore MCC.
doi: 10.1038/nature12807
植物科学：サイトカイニンシグナル伝達が関わる阻害的な場が、葉序にロバスト性をもたらす
Cytokinin signalling inhibitory fields provide robustness to phyllotaxis p.417
How biological systems generate reproducible patterns with high precision is a central question in science. The shoot apical meristem (SAM), a specialized tissue producing plant aerial organs, is a developmental system of choice to address this question. Organs are periodically initiated at the SAM at specific spatial positions and this spatiotemporal pattern defines phyllotaxis. Accumulation of the plant hormone auxin triggers organ initiation, whereas auxin depletion around organs generates inhibitory fields that are thought to be sufficient to maintain these patterns and their dynamics. Here we show that another type of hormone-based inhibitory fields, generated directly downstream of auxin by intercellular movement of the cytokinin signalling inhibitor ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN 6 (AHP6), is involved in regulating phyllotactic patterns. We demonstrate that AHP6-based fields establish patterns of cytokinin signalling in the meristem that contribute to the robustness of phyllotaxis by imposing a temporal sequence on organ initiation. Our findings indicate that not one but two distinct hormone-based fields may be required for achieving temporal precision during formation of reiterative structures at the SAM, thus indicating an original mechanism for providing robustness to a dynamic developmental system.
doi: 10.1038/nature12791
生化学：リピドAを産生する触媒サイクルの間のアシルキャリヤータンパク質の挙動を追跡する
Chasing acyl carrier protein through a catalytic cycle of lipid A production p.422
Acyl carrier protein represents one of the most highly conserved proteins across all domains of life and is nature’s way of transporting hydrocarbon chains in vivo. Notably, type II acyl carrier proteins serve as a crucial interaction hub in primary cellular metabolism by communicating transiently between partner enzymes of the numerous biosynthetic pathways. However, the highly transient nature of such interactions and the inherent conformational mobility of acyl carrier protein have stymied previous attempts to visualize structurally acyl carrier protein tied to an overall catalytic cycle. This is essential to understanding a fundamental aspect of cellular metabolism leading to compounds that are not only useful to the cell, but also of therapeutic value. For example, acyl carrier protein is central to the biosynthesis of the lipid A (endotoxin) component of lipopolysaccharides in Gram-negative microorganisms, which is required for their growth and survival, and is an activator of the mammalian host’s immune system, thus emerging as an important therapeutic target. During lipid A synthesis (Raetz pathway), acyl carrier protein shuttles acyl intermediates linked to its prosthetic 4′-phosphopantetheine group among four acyltransferases, including LpxD. Here we report the crystal structures of three forms of Escherichia coli acyl carrier protein engaging LpxD, which represent stalled substrate and liberated products along the reaction coordinate. The structures show the intricate interactions at the interface that optimally position acyl carrier protein for acyl delivery and that directly involve the pantetheinyl group. Conformational differences among the stalled acyl carrier proteins provide the molecular basis for the association–dissociation process. An unanticipated conformational shift of 4′-phosphopantetheine groups within the LpxD catalytic chamber shows an unprecedented role of acyl carrier protein in product release.
doi: 10.1038/nature12679
生化学：脂肪酸生合成で動的に機能するアシルキャリヤータンパク質の捕捉
Trapping the dynamic acyl carrier protein in fatty acid biosynthesis p.427
Acyl carrier protein (ACP) transports the growing fatty acid chain between enzymatic domains of fatty acid synthase (FAS) during biosynthesis. Because FAS enzymes operate on ACP-bound acyl groups, ACP must stabilize and transport the growing lipid chain. ACPs have a central role in transporting starting materials and intermediates throughout the fatty acid biosynthetic pathway. The transient nature of ACP–enzyme interactions impose major obstacles to obtaining high-resolution structural information about fatty acid biosynthesis, and a new strategy is required to study protein–protein interactions effectively. Here we describe the application of a mechanism-based probe that allows active site-selective covalent crosslinking of AcpP to FabA, the Escherichia coli ACP and fatty acid 3-hydroxyacyl-ACP dehydratase, respectively. We report the 1.9 Å crystal structure of the crosslinked AcpP–FabA complex as a homodimer in which AcpP exhibits two different conformations, representing probable snapshots of ACP in action: the 4′-phosphopantetheine group of AcpP first binds an arginine-rich groove of FabA, then an AcpP helical conformational change locks AcpP and FabA in place. Residues at the interface of AcpP and FabA are identified and validated by solution nuclear magnetic resonance techniques, including chemical shift perturbations and residual dipolar coupling measurements. These not only support our interpretation of the crystal structures but also provide an animated view of ACP in action during fatty acid dehydration. These techniques, in combination with molecular dynamics simulations, show for the first time that FabA extrudes the sequestered acyl chain from the ACP binding pocket before dehydration by repositioning helix III. Extensive sequence conservation among carrier proteins suggests that the mechanistic insights gleaned from our studies may be broadly applicable to fatty acid, polyketide and non-ribosomal biosynthesis. Here the foundation is laid for defining the dynamic action of carrier-protein activity in primary and secondary metabolism, providing insight into pathways that can have major roles in the treatment of cancer, obesity and infectious disease.
doi: 10.1038/nature12810
構造生物学：20面体構造のバクテリオファージΦX174は感染時にDNA輸送のための尾を形成する
Icosahedral bacteriophage ΦX174 forms a tail for DNA transport during infection p.432
Prokaryotic viruses have evolved various mechanisms to transport their genomes across bacterial cell walls. Many bacteriophages use a tail to perform this function, whereas tail-less phages rely on host organelles. However, the tail-less, icosahedral, single-stranded DNA ΦX174-like coliphages do not fall into these well-defined infection processes. For these phages, DNA delivery requires a DNA pilot protein. Here we show that the ΦX174 pilot protein H oligomerizes to form a tube whose function is most probably to deliver the DNA genome across the host’s periplasmic space to the cytoplasm. The 2.4 Å resolution crystal structure of the in vitro assembled H protein’s central domain consists of a 170 Å-long α-helical barrel. The tube is constructed of ten α-helices with their amino termini arrayed in a right-handed super-helical coiled-coil and their carboxy termini arrayed in a left-handed super-helical coiled-coil. Genetic and biochemical studies demonstrate that the tube is essential for infectivity but does not affect in vivo virus assembly. Cryo-electron tomograms show that tubes span the periplasmic space and are present while the genome is being delivered into the host cell’s cytoplasm. Both ends of the H protein contain transmembrane domains, which anchor the assembled tubes into the inner and outer cell membranes. The central channel of the H-protein tube is lined with amide and guanidinium side chains. This may be a general property of viral DNA conduits and is likely to be critical for efficient genome translocation into the host.
doi: 10.1038/nature12816
