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Nature Contents 20 July 2006 (Vol. 442 pp223-328)
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[自然要览] （选自英国Nature杂志，2006年7月20日出版） 封面故事：食物链的复杂性与稳定性 Ecological networks and their fragility/Structural asymmetry and the stability of diverse food webs 食物链网络所反映的是哪些生物吃另一些生物，可用来直观反映生物群落的组 织。食物链网络是复杂的，达尔文也认识到了这一点，他曾形象地将一个食物链 网络比作一个“错综复杂的河岸，它被很多种类的很多植物所覆盖，有鸟儿在灌 木丛上鸣唱，有各种各样的昆虫飞来飞去，还有蠕虫在潮湿的土中爬行”。本期 封面图片（由Sergi Valverde用Netlab软件绘制，svalverde@imim.es）所反映 的是一个根据经验绘制的食物链网络的复杂性，其中的物种是与英国Silwood公 园的金雀花相关的物种。Montoya等人对最近关于生态网络的研究工作进行了评 述，并对一个矛盾现象进行了分析。该矛盾现象是这样的：理论预测复杂的网络 是脆弱的，而复杂性却会发展变化并长期存在。他们得出的结论是，这些网络的 确是复杂的，但没有复杂到我们无法了解它们的程度。在反映进食关系的图谱中 有简化的模式，“错综复杂的河岸”部分地方不像其他地方那么复杂。随着模拟 越来越接近实际，影响生态脆弱性的因素将会变得越来越清楚，这对关于生态影 响和保护的研究工作是有好处的。（Review Article p. 259）本期Nature还刊 登了反映生态问题的其他文章。在一篇参与生态系统生物多样性争论的文章中， Rooney等人发现，真实食物链网络中有一个重复出现的特征：处在食物链顶端的 捕食者会将在生产力和周转率方面都不相同的明显“很快”的能量通道与明显 “很慢”的能量通道耦合起来。理论分析表明，这种耦合是食物链稳定性的关 键。令人吃惊的是，降低生物多样性的人类行为也会逐渐破坏赋予这种稳定性的 结构。所以，现在也许是不要只关注生态系统生物多样性、而要更多关注产生食 物链稳定性的因素的时候了。（Article p. 265; News and Views）我们都承 认，生态问题是复杂的。但是，需要进行与生物多样性有关的决策时，政策制定 者们却没有一个得到大家认可的国际专家组织向他们提供咨询。在气候变化方 面，国际上有IPCC（政府间气候变化专门委员会）。现在，生态学家提出要成立 IMoSEB，其全称为“International Mechanism of Scientific Expertise on Biodiversity”。(Commentary, p. 245) 通过控制温度改变颗粒聚集程度 Granular materials: hot stuff 颗粒材料的处理和存放在很多行业中很重要，通过更好地了解造成颗粒聚集在一 起的因素，有可能对相关技术进行改进。机械搅动通常在用来控制颗粒材料动态 构型的体系中发挥一定作用。但新的研究工作表明，控制温度是另一种办法。在 用玻璃珠所做的试验中，仅仅通过升高温度、然后再降低温度，就能诱导颗粒聚 集程度的可控增加。（Brief Communication p. 257） 关于再发新星RS Oph的观测结果 A star is reborn 今年2月，再发新星RS Ophiuchi (RS Oph)诞生了。每隔20年左右的时间，该双 星体系的白矮星就会从其红色的巨型伴星那里积聚足够多的物质，促成一次热核 爆炸，这种爆炸在我们看来是其亮度由非常暗的12.5等左右增加到5等。两个小 组在本期Nature上报告了对最近爆发的观测结果。Sokoloski等人利用卫星X-射 线观测结果来揭示最初阶段的情况，在最初阶段，爆炸波自由向外传播。在2天 时间内，向外传播的波开始慢下来，说明爆炸所产生的碎片要比从这样一次事件 所预期的数量少得多。O'Brien等人利用最大的陆基射电天文望远镜阵列来对RS Oph进行观测，因而能够在最初发现14天之后首次对一个新星爆炸中的冲击波进 行直接成像观测。所显示的结构表明，该天体正在向一个恒星残体发展演化，类 似于一种二类超新星的演化，但它是在几个月的时间尺度上演化的，而不是在千 年的时间尺度上。（Letters pp. 276, 279） 一种基于石墨薄片的新型复合材料 Nanotubes unwrapped 碳纳米管非凡的机械性能来自它们由之形成的、薄至原子级的碳层（石墨薄片） 的非凡强度和硬度。相比之下，大体积的石墨（一种多晶材料）断裂强度低，容 易因石墨薄片的脱层发生断裂，或在晶体之间的颗粒边界上发生断裂。现在，通 过将石墨薄片与石墨分开、并通过化学方法对其进行调整，Stankovich等人研制 出了一种成本不高的聚合物基质复合材料，它含有散布的石墨薄片，该材料具有 一系列有用的热性能、电性能和机械性能。（Letter p. 282; News and Views） 板块断裂造成地表裂缝 A continent divided (Wright JV) 在2005年9月的一段为期15天的时间内，埃塞俄比亚阿尔法低地60公里长的一 段，因超过2立方公里的熔化岩石注入进该板块中而被撕开，在地表上形成了一 个8米宽的裂缝。事件前后获得的卫星雷达影像表明，这里形成了一系列裂缝， 裂缝两边隆起，地表沉降到了熔化的岩石上。这一系列事件在过程上与发生在冰 岛Krafla 的事件相似，说明大陆板块断裂曾经在阿尔法低地发生过，在板块断 裂过程中，中海洋山脊特征性的轴向分割开始出现。（Letter p. 291; News and Views） 副突变是RNA引导的 How maize bends the rules 副突变是上个世界50年代首次在玉米中发现的，此后曾在其他植物、真菌、甚至 小鼠中发现，它是一个打破常规的遗传模式。大多数情况下，孟德尔的遗传法则 是得到遵守的，基因对独立遗传。副突变是一种相互作用，在这个过程中，一种 基因的一个沉默的等位基因将另一个“积极表达”的等位基因变异，所以它也被 沉寂。现在，利用玉米所做的新的研究工作表明，副突变是RNA引导的。与副突 变和转位子沉寂相关的染色质状态的稳定性要求mop1基因，它为一个依赖于RNA 的RNA聚合酶编码。（Letter p. 295） KLF2的一种新功能 A new role for KLF2 转录因子KLF2长期被认为在控制成熟T细胞的存活和静止中扮演一个关键角色， 因为缺乏KLF2的T细胞会在胸腺中形成，但不能进入周围淋巴器官。一项新的研 究工作对这种表现型提出了另一种解释，这种解释与KLF2作为胸腺细胞和T细胞 迁移的一个调控因子这样一个完全不同的功能是一致的。 KLF（Krüppel类转录 因子）家族的蛋白参与脊椎动物发育的很多方面，并且与若干疾病状态有关。 KLF2这一新发现的功能与不同细胞类型的终端分异所必需的其他一些KLF是相似 的。（Letter p. 299） 能够对组蛋白H3进行去甲基化的酶 Up to the mark 本期Nature上两篇论文识别出了能够从组蛋白H3的Lys 9残体上对一个三甲基官 能团进行去甲基的酶，而该官能团是形成异染色质所需的一个“标志”，以前被 认为是稳定的。Cloos等人发现，GASC1（JMJD2酶家族的一个成员）在过度表达 时能破坏异染色质的结构，并且可能有助于肿瘤的形成。Klose等人发现， JHDM3A（也是一种JMJD2型的酶）的过度表达破坏异染色质的结构。它可能在常 染色质中发挥功能，对转录进行调控。（Letters pp. 307, 312） 蛋白的折叠和展开 Atom-by-atom folding 过去，蛋白折叠通过理论研究一直要比通过实验研究更容易一些。但最近，理论 已经开始被实验所证实。人们一般认为，所有蛋白都是在一个突然的动作中折叠 的，但与这种看法相反的是，一些蛋白事实上是逐渐折叠和展开的，而且整个过 程是在一系列被称为“下坡折叠”的步骤中进行的。Sadqi等人利用一种新颖的 NMR方法来监控一个蛋白从原始状态开始一个原子一个原子地展开过程。他们获 得的结果分辨率高于以前获得的结果，并且证实了折叠是一个统计过程，利用一 种“下坡景观漏斗模型”可以最好地来理解它。另外，协同性可通过绘制一个蛋 白内的原子相互作用来理解。（Letter p. 317; News and Views） |
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ningkeqing
木虫 (正式写手)
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---------------------- NEWS AND VIEWS ---------------------- Plate tectonics: Magma does the splits A minor volcanic eruption in Ethiopia was the main visible clue to a massive injection of magma along the Afar rift last year. Such inconspicuous processes could have been crucial in early continental break-up. Freysteinn Sigmundsson http://www.nature.com/nature/journal/v442/n7100/full/442251a.html Ecology: Asymmetry and stability Ecological communities are dauntingly complex. Nonetheless, ecologists gallantly persevere in eliciting insights about the factors that govern the behaviour and persistence of these messy, tangled webs. Robert D. Holt http://www.nature.com/nature/journal/v442/n7100/full/442252a.html Materials science: Carbon sheet solutions When carbon fibres just won't do, but nanotubes are too expensive, where can cost-conscious materials scientists go to find a practical conductive composite? The answer could lie with graphene sheets. Nicholas A. Kotov http://www.nature.com/nature/journal/v442/n7100/full/442254a.html Microfluids: Clicks and chips Joshua M. Finkelstein http://www.nature.com/nature/journal/v442/n7100/full/442254b.html Structural biology: Proteins downhill all the way The hundreds of hydrogen atoms in a protein can be used as reporters to describe how the protein folds into and out of shape. The results challenge the dogma that this is always an all-or-nothing process. Jeffery W. Kelly http://www.nature.com/nature/journal/v442/n7100/full/442255a.html 50 & 100 years ago http://www.nature.com/nature/journal/v442/n7100/full/442255b.html ---------------------- BRIEF COMMUNICATIONS ---------------------- Granular materials: Packing grains by thermal cycling Small temperature changes can affect the packing of granular materials without mechanical disturbance. K. Chen, J. Cole, C. Conger, J. Draskovic, M. Lohr, K. Klein, T. Scheidemantel and P. Schiffer Abstract: http://www.nature.com/nature/journal/v442/n7100/abs/442257a. html Article: http://www.nature.com/nature/journal/v442/n7100/full/442257a. html CORRIGENDUM Corrigendum http://www.nature.com/nature/journal/v442/n7100/full/442257b.html BRIEF COMMUNICATIONS ARISING Earth science: Is earthquake rupture deterministic? Paul Rydelek and Shigeki Horiuchi Abstract: http://www.nature.com/nature/jou ... bs/nature04963.html Article: http://www.nature.com/nature/jou ... ll/nature04963.html Earth science: Is earthquake rupture deterministic? (Reply) Erik L. Olson and Richard M. Allen Abstract: http://www.nature.com/nature/jou ... bs/nature04964.html Article: http://www.nature.com/nature/jou ... ll/nature04964.html ---------------------- REVIEW ---------------------- Ecological networks and their fragility Jose M. Montoya, Stuart L. Pimm and Ricard V. Sole Abstract: http://www.nature.com/nature/jou ... bs/nature04927.html Article: http://www.nature.com/nature/jou ... ll/nature04927.html ---------------------- ARTICLES ---------------------- Structural asymmetry and the stability of diverse food webs Real food webs are structured so that top predators couple distinct energy channels that differ in both productivity and turnover rate. Theory suggests that such coupling is critical to the maintenance of food web stability, with important implications for conservation and ecosystem management. Neil Rooney, Kevin McCann, Gabriel Gellner and John C. Moore Abstract: http://www.nature.com/nature/jou ... bs/nature04887.html Article: http://www.nature.com/nature/jou ... ll/nature04887.html Mechanism of DNA translocation in a replicative hexameric helicase Examination of the viral E1 hexameric helicase structure finds that a loop of each subunit becomes attached to a nucleotide and remains associated with it during the next six steps of translocation, thereby escorting a single nucleotide through the channel. Eric J. Enemark and Leemor Joshua-Tor Abstract: http://www.nature.com/nature/jou ... bs/nature04943.html Article: http://www.nature.com/nature/jou ... ll/nature04943.html ---------------------- LETTERS ---------------------- An X-ray-emitting blast wave from the recurrent nova RS Ophiuchi J. L. Sokoloski, G. J. M. Luna, K. Mukai and Scott J. Kenyon Abstract: http://www.nature.com/nature/jou ... bs/nature04893.html Article: http://www.nature.com/nature/jou ... ll/nature04893.html An asymmetric shock wave in the 2006 outburst of the recurrent nova RS Ophiuchi T. J. O'Brien, M. F. Bode, R. W. Porcas, T. W. B. Muxlow, S. P. S. Eyres, R. J. Beswick, S. T. Garrington, R. J. Davis and A. Evans Abstract: http://www.nature.com/nature/jou ... bs/nature04949.html Article: http://www.nature.com/nature/jou ... ll/nature04949.html Graphene-based composite materials Individual sheets of graphene can be readily incorporated into a polymer matrix, giving rise to composite materials having potentially useful electronic properties. Sasha Stankovich, Dmitriy A. Dikin, Geoffrey H. B. Dommett, Kevin M. Kohlhaas, Eric J. Zimney, Eric A. Stach, Richard D. Piner, SonBinh T. Nguyen and Rodney S. Ruoff Abstract: http://www.nature.com/nature/jou ... bs/nature04969.html Article: http://www.nature.com/nature/jou ... ll/nature04969.html Seismic reflection images of the Moho underlying melt sills at the East Pacific Rise S. C. Singh, A. J. Harding, G. M. Kent, M. C. Sinha, V. Combier, S. Bazin, C. H. Tong, J. W. Pye, P. J. Barton, R. W. Hobbs, R. S. White and J. A. Orcutt Abstract: http://www.nature.com/nature/jou ... bs/nature04939.html Article: http://www.nature.com/nature/jou ... ll/nature04939.html Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode Tim J. Wright, Cindy Ebinger, Juliet Biggs, Atalay Ayele, Gezahegn Yirgu, Derek Keir and Anna Stork Abstract: http://www.nature.com/nature/jou ... bs/nature04978.html Article: http://www.nature.com/nature/jou ... ll/nature04978.html An RNA-dependent RNA polymerase is required for paramutation in maize Mapping of a gene in maize that functions in paramutation -- where one silent allele of a gene 'mutates' the actively expressed allele, so that it too becomes silenced -- finds that it encodes a protein involved in RNA processing. This research provides support for the involvement of RNAs in paramutation. Mary Alleman, Lyudmila Sidorenko, Karen McGinnis, Vishwas Seshadri, Jane E. Dorweiler, Joshua White, Kristin Sikkink and Vicki L. Chandler Abstract: http://www.nature.com/nature/jou ... bs/nature04884.html Article: http://www.nature.com/nature/jou ... ll/nature04884.html Kruppel-like factor 2 regulates thymocyte and T-cell migration The transcription factor KLF2 has been thought to control survival of T lymphocytes, as KLF2-deficient T cells develop in the thymus, but fail to populate the peripheral lymphoid organs. But this report shows that the phenotype results from an unexpected role of KLF2 in regulating the expression of lymphocyte trafficking molecules. Corey M. Carlson, Bart T. Endrizzi, Jinghai Wu, Xiaojie Ding, Michael A. Weinreich, Elizabeth R. Walsh, Maqsood A. Wani, Jerry B. Lingrel, Kristin A. Hogquist and Stephen C. Jameson Abstract: http://www.nature.com/nature/jou ... bs/nature04882.html Article: http://www.nature.com/nature/jou ... ll/nature04882.html TBC-domain GAPs for Rab GTPases accelerate GTP hydrolysis by a dual-finger mechanism Structural insight into the complex between the GTPase Rab33 and the TBC domain of the GTPase-activating protein Gyp1p reveals that the TBC domain supplies two catalytic residues in trans -- an unexpected dual finger mechanism. Xiaojing Pan, Sudharshan Eathiraj, Mary Munson and David G. Lambright Abstract: http://www.nature.com/nature/jou ... bs/nature04847.html Article: http://www.nature.com/nature/jou ... ll/nature04847.html The putative oncogene GASC1 demethylates tri- and dimethylated lysine 9 on histone H3 One of two papers in this issue that identifies enzymes capable of demethylating a tri-methyl group from Lys 9 of histone H3 -- a mark required for the establishment of heterochromatin and previously considered to be stable. GASC1, a member of the JMJD2 enzyme family, can disrupt heterochromatin structure when overexpressed and may contribute to tumour development. Paul A. C. Cloos, Jesper Christensen, Karl Agger, Alessio Maiolica, Juri Rappsilber, Torben Antal, Klaus H. Hansen and Kristian Helin Abstract: http://www.nature.com/nature/jou ... bs/nature04837.html Article: http://www.nature.com/nature/jou ... ll/nature04837.html The transcriptional repressor JHDM3A demethylates trimethyl histone H3 lysine 9 and lysine 36 One of two papers in this issue that identifies enzymes capable of demethylating a tri-methyl group from Lys 9 of histone H3 -- a mark required for the establishment of heterochromatin and previously considered to be stable. JHDM3A, a member of the JMJD2 enzyme family, can disrupt heterochromatin structure when overexpressed and may function in euchromatin to regulate transcription. Robert J. Klose, Kenichi Yamane, Yangjin Bae, Dianzheng Zhang, Hediye Erdjument-Bromage, Paul Tempst, Jiemin Wong and Yi Zhang Abstract: http://www.nature.com/nature/jou ... bs/nature04853.html Article: http://www.nature.com/nature/jou ... ll/nature04853.html Atom-by-atom analysis of global downhill protein folding Nuclear magnetic resonance is used to monitor unfolding of a protein atom-by-atom from the native state. The results have greater resolution than had been previously achieved, and confirm that folding is a statistical process. Mourad Sadqi, David Fushman and Victor Munoz Abstract: http://www.nature.com/nature/jou ... bs/nature04859.html Article: http://www.nature.com/nature/jou ... ll/nature04859.html CORRIGENDUM Corrigendum: Titan Radar Mapper observations from Cassini's T3 fly-by C. Elachi, S. Wall, M. Janssen, E. Stofan, R. Lopes, R. Kirk, R. Lorenz, J. Lunine, F. Paganelli, L. Soderblom, C. Wood, L. Wye, H. Zebker, Y. Anderson, S. Ostro, M. Allison, R. Boehmer, P. Callahan, P. Encrenaz, E. Flamini, G. Francescetti, Y. Gim, G. Hamilton, S. Hensley, W. Johnson, K. Kelleher, D. Muhleman, G. Picardi, F. Posa, L. Roth, R. Seu, S. Shaffer, B. Stiles, S. Vetrella and R. West http://www.nature.com/nature/jou ... ll/nature05004.html |
2楼2006-07-22 14:11:35