| 2006年08月17日 Nature中英文摘要 | | 点击： 作者： 来源： 时间： 2006-11-12 本站论坛 |
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Volume 442 Number 7104 pp719-846 (17 August 2006)
封面故事：影响核小体定位的因素
真核基因组在活体中不以裸露DNA形式存在，但在被称为染色质的蛋白-DNA复合物中是以裸露DNA形式存在的。染色质含有核小体，它们是紧紧包裹在一个组蛋白核心周围的短DNA片段，排斥大多数结合DNA的蛋白，所以起抑制剂的作用。在一项研究工作中，研究人员将计算方法和实验方法结合起来，用以确定核小体对DNA序列的偏好，并预测整个基因组范围内核小体的组织。酵母基因组编码一个内在的核小体组织，这可以解释活体中核小体位置的大约一半。该编码在不同真核细胞中都高度保留了下来，它的作用是将转录因子引导到它们的结合点，并辅助很多其他的特定染色体功能。本期一篇配发的News and Views文章讨论了DNA序列和其他调控因子在核小体定位中所起的作用。（Article p. 772; News and Views）封面图片（绘图：Helit Sayfan Altman）所示为带有几个核小体的一段染色质。
星系形成过程中一个关键时期的事件观测
配备有最新近红外成像分光镜和适应性光学系统的大型陆基望远镜，能够观测发生在星系形成一个关键时期（“大爆炸”之后约30亿年，当时宇宙只有其现在年龄的约20%）所发生的事件。对这一时期一个正在形成恒星的高红移（z=2.38）星系所做的观测显示了该星系的内部结构。一个巨大的、转动的原始盘，在将气体送往位于中心位置的一个由恒星鼓出的包中的一个正在不断增长的黑洞中。以前，星系的分级积累中所涉及的时间尺度和过程只是一种猜测；现在，它们是所观测到的东西。而且，随着这一时期更多星系得到分析，关于星系形成的模型还可以进一步优化。
火星上的冰盖
本期两篇论文讨论了在火星南方所看到的引人注目的季节变化。火星上的冰盖主要由冷冻的二氧化碳组成，冰盖上有不寻常的暗点，它们被认为是由一块透明的、近乎纯净的CO2冰形成的。Langevin等人提供了来自搭载在“火星奥德赛”上的THEMIS照相机所拍摄的红外和可见光图像，它们与火星上存在一块很厚的透明冰的观点是不一致的。在与该论文相伴的一篇论文中，Kieffer等人报告了他们的红外和可见光数据，这些数据表明，所观测到的景观在入夏很久之后也能保持在CO2冰的温度下，而且它们一定是被带到冰表面上的颗粒物质。他们提出了一个模型，按照该模型，存在一种半透明的、不能渗透的CO2冰盖，在该冰盖的底部会出现升华现象，产生在冰下流动的高速CO2气体流，使冰盖升起，同时产生能将沙子大小的颗粒通过喷孔喷出去的喷射流。
多铁材料和磁电耦合
关于多铁和磁电材料的研究正在重新兴起。多铁材料将铁电晶体稳定的、可切换的电极化与通过铁磁晶体的量子力学交换现象产生的稳定的、可切换的磁化结合了起来。真正的“多铁”材料几乎不存在，而磁性和电性的“磁电耦合”更为普遍。由于这种材料有技术应用前景，所以属于这种类型的一些引人注目的新化合物正在开发当中。
设计通用量子逻辑门已万事俱备
实现现实的量子位的最有希望的方法之一是，利用半导体量子点中的单电子自旋状态。关于这种自旋量子位的一个详细技术建议是在大约10年前发表的，此后，实现这种自旋量子位所需的全部要素（如长寿命自旋态和电子自旋的初始化）已被一一报道出来。现在，最后一步，也是最难的一步也已经完成，那就是驱动单个电子的相干自旋振荡，这是完成量子运算所必需的。这一点是通过施加振荡磁场做到的，这种磁场与电子自旋的进动频率发生共振，是在一个双量子点系统附近的芯片上产生的。现在，设计通用量子逻辑门的一切条件都已具备。
Skyrmion的其他存在形式
现代物理学中一个长期存疑的问题，是按照连续场中可数粒子对“波-粒二象性”进行描述。我们知道，被称为skyrmion的像粒子一样的状态（这些状态是由Tony Skyrme设想出来的）是从微观尺度到宇宙尺度的非线性场模型的一个特点。但迄今为止，我们只确定了skyrmion以激发态存在；当它们被外部场或拓扑缺陷稳定时，以图灵模式存在；在量子霍尔磁体中以自旋图案存在；或在液晶中以蓝相存在。新的理论工作表明，skyrmion还能在不同类型磁性金属中形成稳定的基态，处于这种状态时它们应能够用现代磁性显微镜方法直接观测到。按照这一新理论，skyrmion基态应普遍存在于大量材料中。
用于物体识别的新算法
即便是在吵杂的视觉图像中，人类通常也能够毫不费力地找到相干区域，这是物体识别的关键。在自然观看条件下，电脑算法在完成这项任务时一直不是很成功，部分原因是，早期关于该问题的研究工作只对图像进行了局部计算。现在，一种新方法已经开发出来，它所靠的是图像分割，即对一个图像的所有突出区域进行分析，再将这些区域做成一个有层次的结构。该方法比以前的方法更快，更准确，但所得到的算法使用起来相对比较简单。研究人员通过在由物体构成的一个大数据库中寻找与一个目标物体相匹配的物体的方式，对这种新方法进行了演示。
古生菌在土壤氨的氧化中居主导地位
硝化作用指的是微生物将氨转换成硝酸盐的过程，它是全球氮循环中的一个关键过程。人们曾经普遍假设，专门进行硝化作用的细菌是土壤中在需氧条件下氧化氨的主要细菌。对为名叫“氨单氧酶”的关键酶的一个亚单元编码的amoA基因的丰度所做的分析表明，在来自三个不同气候带的12种不同土壤类型中，来自泉古菌门(Crenarchaeota)的古生菌的amoA基因数量要比细菌的amoA基因数量多3000倍。所以，在原始土壤和农业土壤中，古生菌迄今似乎都是居主导地位的氨氧化剂。
Notch受体在控制干细胞的一个通道中所起的作用
将干细胞用于治疗的一个障碍是，难以控制它们的生长和分化。Androutsellis-Theotokis等人发现，Notch受体在控制胚胎干细胞、胎儿干细胞和成年干细胞的一个通道中扮演一个至关重要的角色，而且向成年大鼠的大脑中施用Notch配体，可帮助大鼠在一次模拟中风之后恢复行动。该发现为以鼓励身体内生的干细胞去修复损伤、而不是试图生长和移植新细胞为目的的疗法铺平了道路。
癌症干细胞的身份
癌症被认为是来自正常组织细胞或定向祖细胞。关键问题是，在后一种情况下，能够自行更新（祖细胞缺乏这种能力）的癌症干细胞是怎样出现的。有一组小鼠白血病干细胞，将少到只有4个的这种细胞注射进小鼠体内，就能诱发白血病。现在，这样的小鼠白血病干细胞已经从通过定向祖细胞中的一个突变患上白血病的小鼠身上分离出来。这使得研究人员有可能利用基因表达筛选的方法来确定这些细胞的共同身份，观察从正常祖细胞向白血病干细胞的转变。 引人注目的是，白血病干细胞大体上能够保持定向祖细胞的基因表达特点，同时激发正常情况下在造血干细胞中表达的一个亚组的基因。至少可以说，这些基因中有些对于白血病干细胞的自行更新是重要的。白血病干细胞和正常干细胞之间的差别，对于开发一种能够选择性地以癌症干细胞为目标的药物的工作来说也许还是好消息。
Contents
Editorials
Round objects p719
Planets are spherical, and the International Astronomical Union's attempt to make this part of their definition has merit.
doi:10.1038/442719a
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Revival in Iran p719
Whatever its motivation, Iran's support for education and science is to be welcomed.
doi:10.1038/442719b
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Preventing cancer p720
More support is required to tackle obesity as a means of cancer prevention.
doi:10.1038/442720a
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Top of pageResearch Highlights
Research highlights p722
doi:10.1038/442722a
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Top of pageNews
Planets are round. Will that do? p724
Astronomers attempt to break deadlock over definition.
Jenny Hogan
doi:10.1038/442724a
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AIDS meeting urged to rethink prevention strategy p724
Researchers seek new ways to fight disease.
Erika Check
doi:10.1038/442724b
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Homing in on the genes for humanity p725
What makes us different from chimps?
Kerri Smith
doi:10.1038/442725a
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Sidelines p726
doi:10.1038/442726a
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Guilty, but no jail sentence for Russian scientist p726
Human-rights groups condemn conviction.
Quirin Schiermeier
doi:10.1038/442726b
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The outlook for Amazonia is dry p726
Drought of 2005 is a taste of things to come.
Jim Giles
doi:10.1038/442726c
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Florida lures research institutes east p729
Sunshine state appeals to Californian expertise.
Rex Dalton
doi:10.1038/442729a
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The methane mystery p730
The claim that living plants emit the greenhouse gas methane has shaken up atmospheric scientists. Quirin Schiermeier talks to the experts trying to make sense of the measurements.
doi:10.1038/442730a
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News in brief p732
doi:10.1038/442732a
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Correction p732
doi:10.1038/442732b
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Top of pageBusiness
More fizz at Pfizer? p734
Young blood is taking the helm at the world's biggest drug firm. Colin Macilwain assesses whether this is likely to revive its share price.
doi:10.1038/442734a
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Top of pageNews Features
Cancer: New fronts in an old war p735
doi:10.1038/442735a
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Cancer: Caught in time p736
The detection of cancer at an early stage in its development can be life-saving. With research efforts under way to find better methods to detect minuscule tumours, Laura Spinney finds out how near some of these cancer 'biomarkers' are to the clinic.
doi:10.1038/442736a
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Cancer: Off by a whisker p739
Much of what we know about cancer comes from studying mice, and potential therapies are tested in the animals. But the differences between the species can scupper the best laid plans of researchers and drug companies, reports Carina Dennis.
doi:10.1038/442739a
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Cancer: The root of the problem p742
Is targeting cancer stem cells a way to finish tumours off once and for all — or just the latest in a long line of false dawns? Alison Abbott looks at a debate that's generating both heat and light.
doi:10.1038/442742a
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Top of pageCorrespondence
Conservation requires multiple approaches p744
Kamaljit S. Bawa
doi:10.1038/442744a
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Researchers should ensure that their actions are lawful p744
Peter Cohen
doi:10.1038/442744b
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Wiki and other ways to share learning online p744
Stephen Caddick
doi:10.1038/442744c
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It's easier to patent plants than to publish research p744
U. C. Lavania
doi:10.1038/442744d
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Top of pageBooks and Arts
Defining moments p745
What are the major principles that controlled the origin of life?
David Penny reviews Singularities: Landmarks on the Pathways of Life by Christian de Duve
doi:10.1038/442745a
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Secret giants p746
Jon Agar reviews Colossus: The Secrets of Bletchley Park's Codebreaking Computers edited by B. Jack Copeland
doi:10.1038/442746a
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Exhibition: Discovering the invisible p747
doi:10.1038/442747a
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Small science, big challenge p747
Julia A. Moore reviews Nanotechnology: New Promises, New Dangers by Toby Shelley
doi:10.1038/442747b
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Top of pageNews and Views
Quantum physics: A spin solo p749
Quantum computers could solve problems insurmountable to conventional computers. The missing ingredient for quantum computing with electron spins is now available — the rotation of a single spin.
Guido Burkard
doi:10.1038/442749a
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Genomics: Predictable packaging p750
Nuclear factors must access specific sites within genomic DNA to function, yet the DNA is bundled up into many nucleosomes. Is the DNA sequence sufficiently informative to predict where each nucleosome will be?
Timothy J. Richmond
doi:10.1038/442750a
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50 & 100 years ago p751
doi:10.1038/442751a
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Solid-state physics: Resistance is futile p752
With the right combination of microwave radiation and magnetic field, two-dimensional electron systems conduct electricity with zero resistance. But is this zero really zero, or is it negative resistance in disguise?
Adam C. Durst
doi:10.1038/442752a
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Astronomy: Young spirals get older p753
These days, galaxies come in very different shapes and sizes. Cutting-edge technologies allow a detailed peek at how things looked in the Universe's early days — 'the same, but different' is the tentative message.
Robert C. Kennicutt, Jr
doi:10.1038/442753a
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Cancer biology: A game of subversion p754
Just as stem cells are crucial for tissue development and regeneration, cancer stem cells underlie tumour formation and maintenance. But do cancer stem cells invariably arise from normal stem cells?
Emmanuelle Passegué
doi:10.1038/442754a
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Obituary: George W. Wetherill (1925–2006) p756
Geochemist, planetary scientist and astrobiologist.
Alan P. Boss
doi:10.1038/442756a
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Top of pageBrief Communications
Silent spread of H5N1 in vaccinated poultry p757
A chink in the protection of a caged flock can dramatically increase the chances of a flu outbreak.
Nicholas J. Savill, Suzanne G. St Rose, Matthew J. Keeling and Mark E. J. Woolhouse
doi:10.1038/442757a
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Top of pageBrief Communications Arising
Cell biology: Nondisjunction, aneuploidy and tetraploidy pE9
Beth A. A. Weaver, Alain D. Silk and Don W. Cleveland
doi:10.1038/nature05139
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Cell biology: Nondisjunction, aneuploidy and tetraploidy (Reply) pE10
Qinghua Shi and Randall W. King
doi:10.1038/nature05140
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Top of pageReview
Multiferroic and magnetoelectric materials p759
W. Eerenstein, N. D. Mathur and J. F. Scott
doi:10.1038/nature05023
Abstract | Full Text | PDF (354K)
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Top of pageArticles
Driven coherent oscillations of a single electron spin in a quantum dot p766
F. H. L. Koppens, C. Buizert, K. J. Tielrooij, I. T. Vink, K. C. Nowack, T. Meunier, L. P. Kouwenhoven and L. M. K. Vandersypen
doi:10.1038/nature05065
Abstract | Full Text | PDF (1,264K) | Supplementary information
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A genomic code for nucleosome positioning p772
Eran Segal, Yvonne Fondufe-Mittendorf, Lingyi Chen, AnnChristine Thåström, Yair Field, Irene K. Moore, Ji-Ping Z. Wang and Jonathan Widom
doi:10.1038/nature04979
Abstract | Full Text | PDF (952K) | Supplementary information
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PML inhibits HIF-1 translation and neoangiogenesis through repression of mTOR p779
Rosa Bernardi, Ilhem Guernah, David Jin, Silvia Grisendi, Andrea Alimonti, Julie Teruya-Feldstein, Carlos Cordon-Cardo, M. Celeste Simon, Shahin Rafii and Pier Paolo Pandolfi
doi:10.1038/nature05029
Abstract | Full Text | PDF (792K) | Supplementary information
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Top of pageLetters
The rapid formation of a large rotating disk galaxy three billion years after the Big Bang p786
R. Genzel, L. J. Tacconi, F. Eisenhauer, N. M. Förster Schreiber, A. Cimatti, E. Daddi, N. Bouché, R. Davies, M. D. Lehnert, D. Lutz, N. Nesvadba, A. Verma, R. Abuter, K. Shapiro, A. Sternberg, A. Renzini, X. Kong, N. Arimoto and M. Mignoli
doi:10.1038/nature05052
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No signature of clear CO2 ice from the 'cryptic' regions in Mars' south seasonal polar cap p790
Yves Langevin, Sylvain Douté, Mathieu Vincendon, François Poulet, Jean-Pierre Bibring, Brigitte Gondet, Bernard Schmitt and F. Forget
doi:10.1038/nature05012
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CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap p793
Hugh H. Kieffer, Philip R. Christensen and Timothy N. Titus
doi:10.1038/nature04945
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Spontaneous skyrmion ground states in magnetic metals p797
U. K. Röler, A. N. Bogdanov and C. Pfleiderer
doi:10.1038/nature05056
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Resonant slow fault slip in subduction zones forced by climatic load stress p802
Anthony R. Lowry
doi:10.1038/nature05055
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Archaea predominate among ammonia-oxidizing prokaryotes in soils p806
S. Leininger, T. Urich, M. Schloter, L. Schwark, J. Qi, G. W. Nicol, J. I. Prosser, S. C. Schuster and C. Schleper
doi:10.1038/nature04983
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Hierarchy and adaptivity in segmenting visual scenes p810
Eitan Sharon, Meirav Galun, Dahlia Sharon, Ronen Basri and Achi Brandt
doi:10.1038/nature04977
First paragraph | Full Text | PDF (411K) | Supplementary information
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Phosphorylation of WAVE1 regulates actin polymerization and dendritic spine morphology p814
Yong Kim, Jee Young Sung, Ilaria Ceglia, Ko-Woon Lee, Jung-Hyuck Ahn, Jonathan M. Halford, Amie M. Kim, Seung P. Kwak, Jong Bae Park, Sung Ho Ryu, Annette Schenck, Barbara Bardoni, John D. Scott, Angus C. Nairn and Paul Greengard
doi:10.1038/nature04976
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Transformation from committed progenitor to leukaemia stem cell initiated by MLL–AF9 p818
Andrei V. Krivtsov, David Twomey, Zhaohui Feng, Matthew C. Stubbs, Yingzi Wang, Joerg Faber, Jason E. Levine, Jing Wang, William C. Hahn, D. Gary Gilliland, Todd R. Golub and Scott A. Armstrong
doi:10.1038/nature04980
First paragraph | Full Text | PDF (637K) | Supplementary information
See also: Editor's summary | News and Views by Passegué
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Notch signalling regulates stem cell numbers in vitro and in vivo p823
Andreas Androutsellis-Theotokis, Ronen R. Leker, Frank Soldner, Daniel J. Hoeppner, Rea Ravin, Steve W. Poser, Maria A. Rueger, Soo-Kyung Bae, Raja Kittappa and Ronald D. G. McKay
doi:10.1038/nature04940
First paragraph | Full Text | PDF (392K) | Supplementary information
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Protein flexibility acclimatizes photosynthetic energy conversion to the ambient temperature p827
Oksana Shlyk-Kerner, Ilan Samish, David Kaftan, Neta Holland, P. S. Maruthi Sai, Hadar Kless and Avigdor Scherz
doi:10.1038/nature04947
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Structure of the catalytic domain of the hepatitis C virus NS2-3 protease p831
Ivo C. Lorenz, Joseph Marcotrigiano, Thomas G. Dentzer and Charles M. Rice
doi:10.1038/nature04975
First paragraph | Full Text | PDF (617K) | Supplementary information
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DNA overwinds when stretched p836
Jeff Gore, Zev Bryant, Marcelo Nöllmann, Mai U. Le, Nicholas R. Cozzarelli and Carlos Bustamante
doi:10.1038/nature04974
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Corrigendum: Structure of the Sec13/31 COPII coat cage p840
Scott M. Stagg, Cemal Gürkan, Douglas M. Fowler, Paul LaPointe, Ted R. Foss, Clinton S. Potter, Bridget Carragher and William E. Balch
doi:10.1038/nature05141
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Top of pageNaturejobs
Prospect
Prospects p841
UK graduate students and postdocs are not getting stipend top-ups, despite available funds.
Paul Smaglik
doi:10.1038/nj7104-841a
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Postdocs and Students
Winning ways p842
Science is cut-throat by nature, but how should young scientists handle working on competitive projects — or worse, getting scooped? Kendall Powell investigates how to release the pressure valve.
Kendall Powell
doi:10.1038/nj7104-842a
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Top of pageFutures
My grandfather's river p846
A stream of memories.
Brenda Cooper
doi:10.1038/442846a
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