Editorials
米オバマ大統領は、地球温暖化問題についての立派な発言を実行に移し、石炭発電や燃料効率の規制に乗り出すべきだ。
More than hot air p.5
US President Barack Obama gave a fine speech on global warming, but now he must deliver on regulations for coal power and greater fuel economy.
doi: 10.1038/499005a
ロシア科学アカデミーの改革を成功させるには、専門家からの助言や協議が不可欠だ。
Russian roulette p.5
Reforms without consultation will destroy the Russian Academy of Sciences.
doi: 10.1038/499005b
移植や研究用の組織提供を促進するためには、「推定同意」を含め、さまざまな取り組みが必要だ。
Presumed consent p.6
More must be done to boost tissue donation for transplantation and research.
doi: 10.1038/499006a
News
EUが、バイオ燃料政策を180度転換する方向へ。
EU debates U-turn on biofuels policy p.13
Key vote could signal withdrawal of support from biodiesel.
doi: 10.1038/499013a
中国が、地下水の汚染浄化に巨額の予算を。
China gears up to tackle tainted water p.14
Government is set to spend 500 million renminbi to clean up groundwater polluted by industry and agriculture.
doi: 10.1038/499015a
米国で新しい科学教育指針が作成され、それを取り入れた州では気候変動学と進化学を高校より前に教えることに。
Evolution makes the grade p.15
Kansas, Kentucky and other states will also teach climate-change science.
doi: 10.1038/499014a
生物工学分野でも、特許重視だった企業にオープンアクセス推進の動きが。
Bioengineers look beyond patents p.16
Synthetic-biology company pushes open-source models.
doi: 10.1038/499016a
米上院で移民制度改革法が可決され、外国人科学者の永住ビザ取得が容易に。
US Senate backs immigration plan p.17
Proposal would lift visa caps for US-trained scientists and engineers.
doi: 10.1038/499017a
EUが、次期研究助成計画「ホライズン2020」の間接費の取り扱いで、ようやく合意へ。
European deal cuts red tape p.18
Horizon 2020 research programme streamlines project reimbursements.
doi: 10.1038/499018a
News Features
組織工学：心臓の作り方
Tissue engineering: How to build a heart p.20
心臓移植を必要とする何万人もの患者の願いに応えようと、移植用心臓の作製の研究が盛んに行われている。
doi: 10.1038/499020a
News & Views
社会科学：子育てのコスト
Social science: The cost of children p.32
生まれる子供の数が減少していることの原因について調査が行われ、経済的な動機は、子供の死亡率あるいは社会的学習よりも影響力が大きいだけでなく、これらの要因間の関係を増強していることがわかった。
doi: 10.1038/nature12257
惑星科学：惑星形成はロバストな過程である
Planetary science: The robustness of planet formation p.33
散開星団中にある2つの惑星の観測から、惑星系は散開星団の形成直後のまだ密度が高い時期には、超新星爆発などの破壊的な事象を超えて生き延びられることがわかった。
doi: 10.1038/nature12405
古代のDNA：100万年前のゲノムに期待
Ancient DNA: Towards a million-year-old genome p.34
ほぼ70万年前という年代の骨から得られた完全なウマゲノムの塩基配列が解読された。これによって、ウマ属の進化について手がかりが得られただけでなく、DNAの保存期間の限界も大幅に延長されることになった。
doi: 10.1038/nature12263
がん：遺伝子調節に迫る変異
Cancer: Mutations close in on gene regulation p.35
急性骨髄性白血病患者に由来する200個のサンプルで、DNAとRNAの塩基配列、遺伝子発現とDNA修飾について全ゲノム解析が行われ、データ統合と検証の準備が整った。これは、このがんの包括的解明を進めることになりそうだ。
doi: 10.1038/499035a
地球科学：深い所にある熱い原因
Earth science: Hot and deep p.37
エチオピアのアファール三角地帯は、その下にある構造プレートが離れるように引っ張られているため、注目に値する。モデルによってこの地溝形成に関連した融解過程の原因と深さが明らかになった。
doi: 10.1038/499037a
がん：胆汁酸がつなぐ肥満とがん
Cancer: An acidic link p.37
肥満だといろいろな種類のがんの発症リスクが高くなるが、その理由は不明である。説明となりそうなのは、腸内微生物が作り出す、炎症誘発性と発がん性を併せ持つ胆汁酸の量が、肥満によって増えるという考えである。
doi: 10.1038/nature12404
マラリア：性行動のタイミングを感知する
Malaria: Sensing when it's time for sex p.38
マラリア原虫は発生段階を切り替えることで伝播を促進する。この切り替えは、膜に結合した小胞を介して行われる原虫間での情報交換によって開始されるらしい。
doi: 10.1038/499038a
生物無機化学：合成化合物によって活性化される酵素
Bioinorganic chemistry: Enzymes activated by synthetic components p.40
水素を発生させる酵素であるHydA1の触媒補助部位の合成類似体は、これまで活性が見られるものがなかった。こうした類似体を酵素の活性部位に組み込むことで、活性に何が必要なのかが明らかにされた。
doi: 10.1038/nature12260
Articles
医学：腎明細胞がんの包括的な分子特性解析
Comprehensive molecular characterization of clear cell renal cell carcinoma OPEN p.43
The Cancer Genome Atlas Research Network reports an integrative analysis of more than 400 samples of clear cell renal cell carcinoma based on genomic, DNA methylation, RNA and proteomic characterisation; frequent mutations were identified in the PI(3)K/AKT pathway, suggesting this pathway might be a potential therapeutic target, among the findings is also a demonstration of metabolic remodelling which correlates with tumour stage and severity.
doi: 10.1038/nature12222
分子生物学：53BP1は、DNA損傷でH2Aの15番目のリシンに誘導されたユビキチン標識を読み取る分子である
53BP1 is a reader of the DNA-damage-induced H2A Lys 15 ubiquitin mark p.50
This study shows that 53BP1 recruitment to sites of DNA damage involves dual recognition of H4K20me2 and H2AK15 histone ubiquitination; the ubiquitin mark and the surrounding epitope on H2A are read by a region of 53BP1 designated the ubiquitination-dependent recruitment motif.
doi: 10.1038/nature12318
Letters
宇宙：散開星団内外での惑星の存在頻度は同じである
The same frequency of planets inside and outside open clusters of stars p.55
Most stars and their planets form in open clusters. Over 95 per cent of such clusters have stellar densities too low (less than a hundred stars per cubic parsec) to withstand internal and external dynamical stresses and fall apart within a few hundred million years. Older open clusters have survived by virtue of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when they formed. Such clusters represent a stellar environment very different from the birthplace of the Sun and other planet-hosting field stars. So far more than 800 planets have been found around Sun-like stars in the field. The field planets are usually the size of Neptune or smaller. In contrast, only four planets have been found orbiting stars in open clusters, all with masses similar to or greater than that of Jupiter. Here we report observations of the transits of two Sun-like stars by planets smaller than Neptune in the billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in the Galaxy.
doi: 10.1038/nature12279
宇宙：後期重爆撃と火山活動による41億〜40億年前の水星全球の地表更新現象
Global resurfacing of Mercury 4.0–4.1 billion years ago by heavy bombardment and volcanism p.59
The most heavily cratered terrains on Mercury have been estimated to be about 4 billion years (Gyr) old, but this was based on images of only about 45 per cent of the surface; even older regions could have existed in the unobserved portion. These terrains have a lower density of craters less than 100 km in diameter than does the Moon, an observation attributed to preferential resurfacing on Mercury. Here we report global crater statistics of Mercury’s most heavily cratered terrains on the entire surface. Applying a recent model for early lunar crater chronology and an updated dynamical extrapolation to Mercury, we find that the oldest surfaces were emplaced just after the start of the Late Heavy Bombardment (LHB) about 4.0–4.1 Gyr ago. Mercury’s global record of large impact basins, which has hitherto not been dated, yields a similar surface age. This agreement implies that resurfacing was global and was due to volcanism, as previously suggested. This activity ended during the tail of the LHB, within about 300–400 million years after the emplacement of the oldest terrains on Mercury. These findings suggest that persistent volcanism could have been aided by the surge of basin-scale impacts during this bombardment.
doi: 10.1038/nature12280
物理：真空スクイーズド状態における原子コヒーレンスの放射減衰の低下
Reduction of the radiative decay of atomic coherence in squeezed vacuum p.62
Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the ordinary vacuum level, allowing measurements that surpass the standard quantum limit in sensitivity. The effects of such ‘squeezed states’ of light on matter were first considered in a prediction of the radiative decay rates of atoms in squeezed vacuum. Despite efforts to demonstrate such effects in experiments with natural atoms, a direct quantitative observation of this prediction has remained elusive. Here we report a twofold reduction of the transverse radiative decay rate of a superconducting artificial atom coupled to continuum squeezed vacuum. The artificial atom is effectively a two-level system formed by the strong interaction between a superconducting circuit and a microwave-frequency cavity. A Josephson parametric amplifier is used to generate quadrature-squeezed electromagnetic vacuum. The observed twofold reduction in the decay rate of the atom allows the transverse coherence time, T2, to exceed the ordinary vacuum decay limit, 2T1. We demonstrate that the measured radiative decay dynamics can be used to reconstruct the Wigner distribution of the itinerant squeezed state. Our results confirm a canonical prediction of quantum optics and should enable new studies of the quantum light–matter interaction.
doi: 10.1038/nature12264
生物無機化学：[FeFe]ヒドロゲナーゼのバイオミメティックな組み立てと活性化
Biomimetic assembly and activation of [FeFe]-hydrogenases p.66
Hydrogenases are the most active molecular catalysts for hydrogen production and uptake, and could therefore facilitate the development of new types of fuel cell. In [FeFe]-hydrogenases, catalysis takes place at a unique di-iron centre (the [2Fe] subsite), which contains a bridging dithiolate ligand, three CO ligands and two CN– ligands. Through a complex multienzymatic biosynthetic process, this [2Fe] subsite is first assembled on a maturation enzyme, HydF, and then delivered to the apo-hydrogenase for activation. Synthetic chemistry has been used to prepare remarkably similar mimics of that subsite, but it has failed to reproduce the natural enzymatic activities thus far. Here we show that three synthetic mimics (containing different bridging dithiolate ligands) can be loaded onto bacterial Thermotoga maritima HydF and then transferred to apo-HydA1, one of the hydrogenases of Chlamydomonas reinhardtii algae. Full activation of HydA1 was achieved only when using the HydF hybrid protein containing the mimic with an azadithiolate bridge, confirming the presence of this ligand in the active site of native [FeFe]-hydrogenases. This is an example of controlled metalloenzyme activation using the combination of a specific protein scaffold and active-site synthetic analogues. This simple methodology provides both new mechanistic and structural insight into hydrogenase maturation and a unique tool for producing recombinant wild-type and variant [FeFe]-hydrogenases, with no requirement for the complete maturation machinery.
doi: 10.1038/nature12239
地球：アファールの地溝形成後期における融解は深部で起こりかつ高温である
Melting during late-stage rifting in Afar is hot and deep p.70
Investigations of a variety of continental rifts and margins worldwide have revealed that a considerable volume of melt can intrude into the crust during continental breakup, modifying its composition and thermal structure. However, it is unclear whether the cause of voluminous melt production at volcanic rifts is primarily increased mantle temperature or plate thinning. Also disputed is the extent to which plate stretching or thinning is uniform or varies with depth with the entire continental lithospheric mantle potentially being removed before plate rupture. Here we show that the extensive magmatism during rifting along the southern Red Sea rift in Afar, a unique region of sub-aerial transition from continental to oceanic rifting, is driven by deep melting of hotter-than-normal asthenosphere. Petrogenetic modelling shows that melts are predominantly generated at depths greater than 80 kilometres, implying the existence of a thick upper thermo-mechanical boundary layer in a rift system approaching the point of plate rupture. Numerical modelling of rift development shows that when breakup occurs at the slow extension rates observed in Afar, the survival of a thick plate is an inevitable consequence of conductive cooling of the lithosphere, even when the underlying asthenosphere is hot. Sustained magmatic activity during rifting in Afar thus requires persistently high mantle temperatures, which would allow melting at high pressure beneath the thick plate. If extensive plate thinning does occur during breakup it must do so abruptly at a late stage, immediately before the formation of the new ocean basin.
doi: 10.1038/nature12292
進化：更新世中期初頭のウマのゲノム塩基配列を用いたウマ属進化の再検討
Recalibrating Equus evolution using the genome sequence of an early Middle Pleistocene horse p.74
The rich fossil record of equids has made them a model for evolutionary processes. Here we present a 1.12-times coverage draft genome from a horse bone recovered from permafrost dated to approximately 560–780 thousand years before present (kyr bp). Our data represent the oldest full genome sequence determined so far by almost an order of magnitude. For comparison, we sequenced the genome of a Late Pleistocene horse (43 kyr bp), and modern genomes of five domestic horse breeds (Equus ferus caballus), a Przewalski’s horse (E. f. przewalskii) and a donkey (E. asinus). Our analyses suggest that the Equus lineage giving rise to all contemporary horses, zebras and donkeys originated 4.0–4.5 million years before present (Myr bp), twice the conventionally accepted time to the most recent common ancestor of the genus Equus. We also find that horse population size fluctuated multiple times over the past 2 Myr, particularly during periods of severe climatic changes. We estimate that the Przewalski’s and domestic horse populations diverged 38–72 kyr bp, and find no evidence of recent admixture between the domestic horse breeds and the Przewalski’s horse investigated. This supports the contention that Przewalski’s horses represent the last surviving wild horse population. We find similar levels of genetic variation among Przewalski’s and domestic populations, indicating that the former are genetically viable and worthy of conservation efforts. We also find evidence for continuous selection on the immune system and olfaction throughout horse evolution. Finally, we identify 29 genomic regions among horse breeds that deviate from neutrality and show low levels of genetic variation compared to the Przewalski’s horse. Such regions could correspond to loci selected early during domestication.
doi: 10.1038/nature12323
遺伝学：ヒトにおけるタンパク質存在量の変動と遺伝的制御
Variation and genetic control of protein abundance in humans p.79
Gene expression differs among individuals and populations and is thought to be a major determinant of phenotypic variation. Although variation and genetic loci responsible for RNA expression levels have been analysed extensively in human populations, our knowledge is limited regarding the differences in human protein abundance and the genetic basis for this difference. Variation in messenger RNA expression is not a perfect surrogate for protein expression because the latter is influenced by an array of post-transcriptional regulatory mechanisms, and, empirically, the correlation between protein and mRNA levels is generally modest. Here we used isobaric tag-based quantitative mass spectrometry to determine relative protein levels of 5,953 genes in lymphoblastoid cell lines from 95 diverse individuals genotyped in the HapMap Project. We found that protein levels are heritable molecular phenotypes that exhibit considerable variation between individuals, populations and sexes. Levels of specific sets of proteins involved in the same biological process covary among individuals, indicating that these processes are tightly regulated at the protein level. We identified cis-pQTLs (protein quantitative trait loci), including variants not detected by previous transcriptome studies. This study demonstrates the feasibility of high-throughput human proteome quantification that, when integrated with DNA variation and transcriptome information, adds a new dimension to the characterization of gene expression regulation.
doi: 10.1038/nature12223
神経科学：ショウジョウバエの摂食運動プログラムに指令を下す1対の介在ニューロン
A single pair of interneurons commands the Drosophila feeding motor program p.83
Many feeding behaviours are the result of stereotyped, organized sequences of motor patterns. These patterns have been the subject of neuroethological studies, such as electrophysiological characterization of neurons governing prey capture in toads. However, technical limitations have prevented detailed study of the functional role of these neurons, a common problem for vertebrate organisms. Complexities involved in studies of whole-animal behaviour can be resolved in Drosophila, in which remote activation of brain cells by genetic means enables us to examine the nervous system in freely moving animals to identify neurons that govern a specific behaviour, and then to repeatedly target and manipulate these neurons to characterize their function. Here we show neurons that generate the feeding motor program in Drosophila. We carried out an unbiased screen using remote neuronal activation and identified a critical pair of brain cells that induces the entire feeding sequence when activated. These ‘feeding neurons’ (here abbreviated to Fdg neurons for brevity) are also essential for normal feeding as their suppression or ablation eliminates sugar-induced feeding behaviour. Activation of a single Fdg neuron induces asymmetric feeding behaviour and ablation of a single Fdg neuron distorts the sugar-induced feeding behaviour to become asymmetric, indicating the direct role of these neurons in shaping motor-program execution. Furthermore, recording neuronal activity and calcium imaging simultaneously during feeding behaviour reveals that the Fdg neurons respond to food presentation, but only in starved flies. Our results demonstrate that Fdg neurons operate firmly within the sensorimotor watershed, downstream of sensory and metabolic cues and at the top of the feeding motor hierarchy, to execute the decision to feed.
doi: 10.1038/nature12208
細胞：新規細胞表面マーカーを用いた高分解能解析によって明らかになったiPS細胞へのルート
High-resolution analysis with novel cell-surface markers identifies routes to iPS cells p.88
The generation of induced pluripotent stem (iPS) cells presents a challenge to normal developmental processes. The low efficiency and heterogeneity of most methods have hindered understanding of the precise molecular mechanisms promoting, and roadblocks preventing, efficient reprogramming. Although several intermediate populations have been described, it has proved difficult to characterize the rare, asynchronous transition from these intermediate stages to iPS cells. The rapid expansion of minor reprogrammed cells in the heterogeneous population can also obscure investigation of relevant transition processes. Understanding the biological mechanisms essential for successful iPS cell generation requires both accurate capture of cells undergoing the reprogramming process and identification of the associated global gene expression changes. Here we demonstrate that in mouse embryonic fibroblasts, reprogramming follows an orderly sequence of stage transitions, marked by changes in the cell-surface markers CD44 and ICAM1, and a Nanog–enhanced green fluorescent protein (Nanog–eGFP) reporter. RNA-sequencing analysis of these populations demonstrates two waves of pluripotency gene upregulation, and unexpectedly, transient upregulation of several epidermis-related genes, demonstrating that reprogramming is not simply the reversal of the normal developmental processes. This novel high-resolution analysis enables the construction of a detailed reprogramming route map, and the improved understanding of the reprogramming process will lead to new reprogramming strategies.
doi: 10.1038/nature12243
細胞：ZFP36L2は前期赤芽球バースト形成単位前駆細胞の自己複製に必要である
ZFP36L2 is required for self-renewal of early burst-forming unit erythroid progenitors p.92
Stem cells and progenitors in many lineages undergo self-renewing divisions, but the extracellular and intracellular proteins that regulate this process are largely unknown. Glucocorticoids stimulate red blood cell formation by promoting self-renewal of early burst-forming unit–erythroid (BFU–E) progenitors. Here we show that the RNA-binding protein ZFP36L2 is a transcriptional target of the glucocorticoid receptor (GR) in BFU–Es and is required for BFU–E self-renewal. ZFP36L2 is normally downregulated during erythroid differentiation from the BFU–E stage, but its expression is maintained by all tested GR agonists that stimulate BFU–E self-renewal, and the GR binds to several potential enhancer regions of ZFP36L2. Knockdown of ZFP36L2 in cultured BFU–E cells did not affect the rate of cell division but disrupted glucocorticoid-induced BFU–E self-renewal, and knockdown of ZFP36L2 in transplanted erythroid progenitors prevented expansion of erythroid lineage progenitors normally seen following induction of anaemia by phenylhydrazine treatment. ZFP36L2 preferentially binds to messenger RNAs that are induced or maintained at high expression levels during terminal erythroid differentiation and negatively regulates their expression levels. ZFP36L2 therefore functions as part of a molecular switch promoting BFU–E self-renewal and a subsequent increase in the total numbers of colony-forming unit–erythroid (CFU–E) progenitors and erythroid cells that are generated.
doi: 10.1038/nature12215
医学：肥満が誘発する腸内細菌代謝産物が、細胞老化関連分泌表現型を介して肝がん発症を促進する
Obesity-induced gut microbial metabolite promotes liver cancer through senescence secretome p.97
Obesity has become more prevalent in most developed countries over the past few decades, and is increasingly recognized as a major risk factor for several common types of cancer. As the worldwide obesity epidemic has shown no signs of abating, better understanding of the mechanisms underlying obesity-associated cancer is urgently needed. Although several events were proposed to be involved in obesity-associated cancer, the exact molecular mechanisms that integrate these events have remained largely unclear. Here we show that senescence-associated secretory phenotype (SASP) has crucial roles in promoting obesity-associated hepatocellular carcinoma (HCC) development in mice. Dietary or genetic obesity induces alterations of gut microbiota, thereby increasing the levels of deoxycholic acid (DCA), a gut bacterial metabolite known to cause DNA damage. The enterohepatic circulation of DCA provokes SASP phenotype in hepatic stellate cells (HSCs), which in turn secretes various inflammatory and tumour-promoting factors in the liver, thus facilitating HCC development in mice after exposure to chemical carcinogen. Notably, blocking DCA production or reducing gut bacteria efficiently prevents HCC development in obese mice. Similar results were also observed in mice lacking an SASP inducer or depleted of senescent HSCs, indicating that the DCA–SASP axis in HSCs has key roles in obesity-associated HCC development. Moreover, signs of SASP were also observed in the HSCs in the area of HCC arising in patients with non-alcoholic steatohepatitis, indicating that a similar pathway may contribute to at least certain aspects of obesity-associated HCC development in humans as well. These findings provide valuable new insights into the development of obesity-associated cancer and open up new possibilities for its control.
doi: 10.1038/nature12347
免疫：自己組織化インフルエンザナノ粒子ワクチンは広範囲中和性のH1N1抗体を誘導する
Self-assembling influenza nanoparticle vaccines elicit broadly neutralizing H1N1 antibodies p.102
Influenza viruses pose a significant threat to the public and are a burden on global health systems. Each year, influenza vaccines must be rapidly produced to match circulating viruses, a process constrained by dated technology and vulnerable to unexpected strains emerging from humans and animal reservoirs. Here we use knowledge of protein structure to design self-assembling nanoparticles that elicit broader and more potent immunity than traditional influenza vaccines. The viral haemagglutinin was genetically fused to ferritin, a protein that naturally forms nanoparticles composed of 24 identical polypeptides. Haemagglutinin was inserted at the interface of adjacent subunits so that it spontaneously assembled and generated eight trimeric viral spikes on its surface. Immunization with this influenza nanoparticle vaccine elicited haemagglutination inhibition antibody titres more than tenfold higher than those from the licensed inactivated vaccine. Furthermore, it elicited neutralizing antibodies to two highly conserved vulnerable haemagglutinin structures that are targets of universal vaccines: the stem and the receptor binding site on the head. Antibodies elicited by a 1999 haemagglutinin–nanoparticle vaccine neutralized H1N1 viruses from 1934 to 2007 and protected ferrets from an unmatched 2007 H1N1 virus challenge. This structure-based, self-assembling synthetic nanoparticle vaccine improves the potency and breadth of influenza virus immunity, and it provides a foundation for building broader vaccine protection against emerging influenza viruses and other pathogens.
doi: 10.1038/nature12202
構造生物学：真核生物カルシウム/プロトン交換輸送体で見られる交互アクセスの構造的基盤
Structural basis for alternating access of a eukaryotic calcium/proton exchanger p.107
Eukaryotic Ca2+ regulation involves sequestration into intracellular organelles, and expeditious Ca2+ release into the cytosol is a hallmark of key signalling transduction pathways. Bulk removal of Ca2+ after such signalling events is accomplished by members of the Ca2+:cation (CaCA) superfamily. The CaCA superfamily includes the Na+/Ca2+ (NCX) and Ca2+/H+ (CAX) antiporters, and in mammals the NCX and related proteins constitute families SLC8 and SLC24, and are responsible for the re-establishment of Ca2+ resting potential in muscle cells, neuronal signalling and Ca2+ reabsorption in the kidney. The CAX family members maintain cytosolic Ca2+ homeostasis in plants and fungi during steep rises in intracellular Ca2+ due to environmental changes, or following signal transduction caused by events such as hyperosmotic shock, hormone response and response to mating pheromones. The cytosol-facing conformations within the CaCA superfamily are unknown, and the transport mechanism remains speculative. Here we determine a crystal structure of the Saccharomyces cerevisiae vacuolar Ca2+/H+ exchanger (Vcx1) at 2.3 Å resolution in a cytosol-facing, substrate-bound conformation. Vcx1 is the first structure, to our knowledge, within the CAX family, and it describes the key cytosol-facing conformation of the CaCA superfamily, providing the structural basis for a novel alternating access mechanism by which the CaCA superfamily performs high-throughput Ca2+ transport across membranes.
doi: 10.1038/nature12233
構造生物学：重要なシャペロンであるFACTによるヒストンH2A–H2B認識の構造基盤
Structural basis of histone H2A–H2B recognition by the essential chaperone FACT p.111
Facilitates chromatin transcription (FACT) is a conserved histone chaperone that reorganizes nucleosomes and ensures chromatin integrity during DNA transcription, replication and repair. Key to the broad functions of FACT is its recognition of histones H2A–H2B (ref. 2). However, the structural basis for how histones H2A–H2B are recognized and how this integrates with the other functions of FACT, including the recognition of histones H3–H4 and other nuclear factors, is unknown. Here we reveal the crystal structure of the evolutionarily conserved FACT chaperone domain Spt16M from Chaetomium thermophilum, in complex with the H2A–H2B heterodimer. A novel ‘U-turn’ motif scaffolded onto a Rtt106-like module embraces the α1 helix of H2B. Biochemical and in vivo assays validate the structure and dissect the contribution of histone tails and H3–H4 towards Spt16M binding. Furthermore, we report the structure of the FACT heterodimerization domain that connects FACT to replicative polymerases. Our results show that Spt16M makes several interactions with histones, which we suggest allow the module to invade the nucleosome gradually and block the strongest interaction of H2B with DNA. FACT would thus enhance ‘nucleosome breathing’ by re-organizing the first 30 base pairs of nucleosomal histone–DNA contacts. Our snapshot of the engagement of the chaperone with H2A–H2B and the structures of all globular FACT domains enable the high-resolution analysis of the vital chaperoning functions of FACT, shedding light on how the complex promotes the activity of enzymes that require nucleosome reorganization.
doi: 10.1038/nature12242
