Catálogo de publicaciones - revistas

<jats:p>A model shows that REDD (reducing emissions from deforestation and degradation) can be extended to biodiversity conservation.</jats:p>

<jats:title>Nascent Chains Revealed</jats:title> <jats:p> Detailed analysis of protein translation and translocation across membranes requires the identification and structural analysis of intermediates involved in these processes (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5958" page="1352" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1183690">Kampmann and Blobel</jats:related-article> </jats:bold> ). <jats:bold> Seidelt <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1412" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177662">1412</jats:related-article> , published online 29 October) report the visualization by cryo-electron microscopy of a nascent polypeptide chain in the tunnel of the ribosome at 5.8 angstroms. This resolution allows analysis of the conformation and distinct contacts of the nascent chain within the ribosomal tunnel, which suggests a mechanism by which translational stalling is induced by this peptide. Protein translocation across cellular membranes involves the Sec61 protein, a component of a protein-conducting channel. Whether Sec61 acts as a monomer or as an oligomer during protein translocation has been unclear. <jats:bold> Becker <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1369" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178535">1369</jats:related-article> , published online 29 October) describe active yeast and mammalian ribosome-Sec61 structures that show the Sec61 complex interacting with the ribosome and a nascent secretory protein signal sequence. The analysis unambiguously reveals that the active protein-conducting channel is a single Sec61 copy with its central pore serving as conduit for the nascent polypeptide. </jats:p>

<jats:title>ABA Receptor Up Close</jats:title> <jats:p> Plants face a variety of environmental stresses, including drought, salinity, and cold. In the face of such stresses, the plant hormone abscisic acid (ABA) triggers adaptive physiological responses. <jats:bold> Nishimura <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1373" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181829">1373</jats:related-article> , published online 22 October; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5958" page="1356" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1184135">Sussman and Phillips</jats:related-article> </jats:bold> ) have now analyzed the crystal structure of one member of the ABA receptor family, PYR1 (pyrabactin resistance 1). The ABA molecule binds within an internal pocket of PYR1, where it probably induces a conformational change. </jats:p>

<jats:title>Elliptical Galaxy Evolution</jats:title> <jats:p> Our closest elliptical galaxy, M32, represents a rare class of elliptical galaxies that are too compact for their luminosities. Only a handful of elliptical galaxies with luminosities and sizes comparable to M32 have been found, making it difficult to understand how they evolved. <jats:bold> Chilingarian <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1379" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1175930">1379</jats:related-article> , published online 1 October) present a sample of 21 compact elliptical galaxies gathered through automated data mining of the Hubble Space Telescope Legacy Archive and other databases by means of virtual observatory tools. The results suggest that tidal stripping of more massive progenitor galaxies produces compact elliptical galaxies. </jats:p>

<jats:title>One More Vibration</jats:title> <jats:p> The beryllium dimer has puzzled chemists for the better part of a century because its bond, though weak by molecular standards, is much stronger than standard bonding frameworks would predict. Recent spectroscopic measurements have characterized the molecule in great detail, but leave open the question of whether a high-energy vibrational state might lie just below the threshold for scission of the bond. <jats:bold> Patkowski <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1382" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181017">1382</jats:related-article> ) have now derived a potential energy function, based on high-level theoretical calculations and, by slightly modifying it through fitting to the experimental data, obtained strong evidence for the presence of the upper vibrational state. Taken together with the measured spectra, these results offer a well-grounded basis for understanding the unusual molecule. </jats:p>

<jats:title>Electrolysis at Nickel</jats:title> <jats:p> One drawback of solar and wind power is the need for an efficient storage system to release accumulated energy when neither source is readily available (during still nights, for example). Hydrogen derived from electrolysis of water is potentially a useful medium for this purpose, but catalyzing the interconversion efficiently at large scale would currently require a substantial amount of the scarce precious metal platinum. An alternative approach would be to mimic natural enzymatic reactions, which accomplish the interconversion using hydrogenases that incorporate the more abundant metals iron and nickel. In this vein, <jats:bold> Le Goff <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1384" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1179773">1384</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5958" page="1355" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1183836">Hambourger and Moore</jats:related-article> </jats:bold> ) have lightly modified a hydrogenase-inspired nickel complex in order to append it to a conductive carbon nanotube support. The resulting hybrid material shows promising catalytic efficiency for reversible aqueous electrolysis in a standard apparatus. </jats:p>

<jats:title>Earth's Plume Plumbing</jats:title> <jats:p> Volcanic hot spots, such as the one that continues to build the Hawaiian Islands, are thought to form by one of two mechanisms: Either mantle plumes bring hot, buoyant material to the surface from deep within the Earth's interior, or extensive processing of the upper mantle by plate tectonics causes localized volcanism in stressed or heterogeneous crust. <jats:bold> Wolfe <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1388" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1180165">1388</jats:related-article> ; see the cover; see the news story by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5958" page="1330" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.2009.326.5958.326_1330">Kerr</jats:related-article> </jats:bold> ) used an extensive array of ocean-bottom and land-based seismometers to reveal the structure of the mantle beneath Hawaii. These high-resolution images reveal a high-temperature plume originating from the lower mantle. </jats:p>

<jats:title>A Happy Marriage</jats:title> <jats:p> The fluxes of CO <jats:sub>2</jats:sub> between the atmosphere and ocean are large and variable, and understanding why the concentration of atmospheric CO <jats:sub>2</jats:sub> changes as it does, depends on accurately determining the details of those fluxes. One of the major obstacles in the way of quantifying this exchange is that there are too few measurements available, both temporally and geographically. <jats:bold> Watson <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1391" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177394">1391</jats:related-article> ) report results from a happy marriage of science and commerce—data collected by instruments fitted onto commercial ships plying the waters of the North Atlantic Ocean—that has generated the largest and most comprehensive set of measurements of ocean pCO <jats:sub>2</jats:sub> ever collected. These data allow the oceanic CO <jats:sub>2</jats:sub> sink to be monitored with unprecedented accuracy and will help researchers precisely map regional interannual air-sea fluxes. </jats:p>

<jats:title> CO <jats:sub>2</jats:sub> and Miocene Climate Change </jats:title> <jats:p> Atmospheric carbon dioxide is a powerful greenhouse gas believed to be one of the most important determinants of climate. Ice cores provide a detailed and direct record of CO <jats:sub>2</jats:sub> concentrations over the past 800,000 years, but not earlier. <jats:bold> Tripati <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1394" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178296">1394</jats:related-article> , published online 8 October) report B/Ca measurements of planktonic foraminifera, from which they can infer atmospheric CO <jats:sub>2</jats:sub> concentrations, for the past 20 million years. The concentration of atmospheric CO <jats:sub>2</jats:sub> was similar to preindustrial values for the past 10 millions years, but between 15 and 20 million years ago, during the warm lower Miocene epoch, CO <jats:sub>2</jats:sub> was more abundant, and major climate transitions toward cooler conditions occurred when CO <jats:sub>2</jats:sub> decreased substantially. </jats:p>

<jats:title>Biofuel Backfire</jats:title> <jats:p> For compelling economical, geopolitical, and environmental reasons, biofuels are considered an attractive alternative to fossil fuels for meeting future global energy demands. <jats:bold> Melillo <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1397" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1180251">1397</jats:related-article> , published online 22 October), however, suggest that a few serious drawbacks related to land use need to be considered. Based on a combined biogeochemistry and economic model, indirect land use (for example, clearing forested land for food crops to compensate for increased biofuel crop production on current farmlands) is predicted to generate more soil carbon loss than directly harvesting biofuel crops. Furthermore, increased fertilizer use for biofuels will add large amounts of nitrous oxide—a more effective heat-trapping molecule than carbon dioxide—to the atmosphere. Policy decisions regarding land and crop management thus need to consider the long-term implications of increased biofuel production. </jats:p>