Catálogo de publicaciones - revistas

<jats:title>Wind of Change</jats:title> <jats:p> The flow of interstellar gas and dust through the solar system was thought to be unvarying, but <jats:bold> Frisch <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1080" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239925">1080</jats:related-article> ) show that there has been a significant variation of the direction of the flow of interstellar helium through the solar system over the past 40 years. The data, collected by 10 different spacecraft over much of the space age, hint of changes rather than constancy in the solar system's galactic environment. </jats:p>

<jats:title>Pushy Black Hole</jats:title> <jats:p> The giant black holes that sit at the centers of most galaxies influence the way galaxies evolve in poorly understood ways. <jats:bold> Morganti <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1082" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1240436">1082</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="6150" page="1073" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1243114">McNamara</jats:related-article> </jats:bold> ) have acquired high-resolution radio images of a galaxy with an actively accreting black hole from which a jet of relativistic particles emanates. The observations show that a cloud of neutral hydrogen gas is being driven outward, possibly limiting star formation and galaxy growth. </jats:p>

<jats:title>Downs and Ups</jats:title> <jats:p> Every spring, the concentration of CO <jats:sub>2</jats:sub> in the atmosphere of the Northern Hemisphere decreases as terrestrial vegetation grows, and every fall, CO <jats:sub>2</jats:sub> rises as vegetation dies and rots. Climate change has destabilized the seasonal cycle of atmospheric CO <jats:sub>2</jats:sub> such that <jats:bold> Graven <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1085" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239207">1085</jats:related-article> , published online 8 August; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1075" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242004">Fung</jats:related-article> </jats:bold> ) have found that the amplitude of the seasonal cycle has exceeded 50% at some latitudes. The only way to explain this increase is if extratropical land ecosystems are growing and shrinking more than they did half a century ago, as a result of changes in the structure and composition of northern ecosystems. </jats:p>

<jats:title>Stitching in Fluoroacetate</jats:title> <jats:p> Polyketide synthase enzymes stitch together an impressively diverse series of organic compounds from simple acetate and propionate building blocks. <jats:bold> Walker <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1089" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242345">1089</jats:related-article> ) now show that these biochemical pathways can be engineered to incorporate fluoroacetate—a primary product of the only known native enzymatic fluorination route—into tri- and tetraketides. In <jats:italic>Escherichia coli</jats:italic> cells, this process shows potential as a versatile means of inserting fluorine substituents into a range of complex molecules for use in pharmaceutical and agrochemical research. </jats:p>

<jats:title>Quantum Collision Course</jats:title> <jats:p> Our experience of a world apparently governed by classical physics is a consequence of the fact that quantum mechanical effects average out in size regimes much larger than nanometers. Even at the molecular level, the quantized nature of rotational energy distributions is often obscured by averaging effects. <jats:bold> Chefdeville <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1094" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241395">1094</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1076" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1244109"> <jats:bold>Casavecchia and Alexander</jats:bold> </jats:related-article> ) have observed a striking manifestation of quantized rotation in the scattering trajectories of colliding H <jats:sub>2</jats:sub> and O <jats:sub>2</jats:sub> molecular beams. The experimentally resolved partial wave resonances show essentially complete agreement with theoretical calculations and deviate starkly from classical collision paradigms. </jats:p>

<jats:title>Absolute Images</jats:title> <jats:p> Molecules are held together by a balance of charge between negative electrons and positive nuclei. When multiple electrons are expelled by laser irradiation, the remaining, mutually repulsive nuclei fly apart in a Coulomb explosion. Instead of traditional x-ray diffraction methods that require crystalline samples, <jats:bold> Pitzer <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1096" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1240362">1096</jats:related-article> ) show that by tracking the fragment trajectories from laser-induced Coulomb explosions of relatively simple gas phase molecules, they can determine the absolute stereochemical configuration of enantiomers (mirror-image isomers). </jats:p>

<jats:title>Plant Protection</jats:title> <jats:p> The Convention on Biological Diversity's 20 Aichi Targets, agreed in October 2010, extend to 2020 an international commitment to halt the loss of biodiversity. Using data from “The Plant List” ( <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://www.theplantlist.org">www.theplantlist.org</jats:ext-link> ), <jats:bold> Joppa <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1100" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241706">1100</jats:related-article> ), show that ∼65% of plant species are endemic to 17% of the terrestrial land surface and include many islands, with mainland contributions concentrated heavily in central and southern America and Asia. These regions include 75% of all plant species. These regions are also important for terrestrial vertebrates—containing most of all—bird, mammal, and amphibian species, but less than one-sixth of this land surface is under protection. </jats:p>

<jats:title>Lignin Biosynthesis Complications</jats:title> <jats:p> Lignin is a polymer that lends its sturdy properties to wood and makes plant cell walls tougher, which creates problems for chemists converting cellulosic plant biomass into biofuels. <jats:bold> Vanholme <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1103" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241602">1103</jats:related-article> , published online 15 August; see the cover) have identified a new step in the biosynthetic pathway of lignin in <jats:italic>Arabidopsis</jats:italic> in which caffeoyl shikimate esterase catalyzes synthesis of caffeate. Cellulose from mutant plants, which had reduced amounts of lignin, was more efficiently processed into glucose. </jats:p>

<jats:title>More Determined Sex</jats:title> <jats:p> Although several transcription factors participate in mammalian sex determination, the contribution from specific epigenetic regulation is just being revealed. <jats:bold> Kuroki <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1106" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239864">1106</jats:related-article> ) show that a JmjC domain–containing protein, Jmjd1a, catalyzes H3K9 demethylation of the Y-linked sex-determining gene <jats:italic>Sry</jats:italic> in mice to enable its expression above the required threshold level. Ablation of Jmjd1a function results in mouse male-to-female sex reversal, hence not only revealing a mechanism of <jats:italic>Sry</jats:italic> regulation but also the pivotal role of epigenetic regulation in mammalian sex determination. </jats:p>

<jats:title>Fatal Chimeras</jats:title> <jats:p> Impaired DNA-methylation maintenance during early embryonic development may cause imprinting-related diseases. <jats:bold> Lorthongpanich <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6150" page="1110" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1240617">1110</jats:related-article> ) have devised a sensitive assay to probe multiple imprinted gene loci for their DNA-methylation state at the single-cell level. Blastomeres with defective imprinting showed complex, epigenetic chimeras developed with fatal defects. Pronuclear transfer restored normal mouse development, offering a therapeutic strategy to overcome epigenetic defects caused by maternal insufficiencies. </jats:p>