Catálogo de publicaciones - revistas

<jats:title>Continental Growth Spurts</jats:title> <jats:p> The appearance and persistence of continents through geologic time has influenced most processes on Earth, from the evolution of new species to the climate. The relative proportion of newly formed crust compared to reworked, or destroyed, older crust reveals which processes controlled continental growth. Based on the combined analyses of Hf-Pb and O isotopes in zircon minerals, <jats:bold> Dhuime <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="1334" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1216066">1334</jats:related-article> ) measured continuous but variable rates of new crustal production throughout Earth's history. Increased rates of crustal destruction starting around 3 billion years ago coincide with the onset of subduction-drive plate tectonics, slowing down the overall rate of crustal growth. </jats:p>

<jats:title>Which Electron Went Where?</jats:title> <jats:p> When strong laser fields pull electrons out of atoms or molecules and then send them careening back, the light released on recollision can offer direct insight into local attosecond-scale behavior, or it can be processed into attosecond pulses for probing other samples. When polyatomic molecules are involved, however, it is not always clear which of their electrons are being manipulated by the laser field. <jats:bold> Boguslavskiy <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="1336" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1212896">1336</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6074" page="1314" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1219486"> <jats:bold>Gühr</jats:bold> </jats:related-article> ) present a technique for exploring this question. Simultaneous tracking of electrons and fragment molecular ions during strong-field ionization of hydrocarbons revealed the different pathways involved. </jats:p>

<jats:title>Bands That Separate</jats:title> <jats:p> In organic photovoltaic devices, the charge carriers that form at the interface between donor and acceptor layers—the electrons and holes—form bound states called excitons. Efficient current generation requires some mechanism for their separation and for the movement of free carriers to the electrodes. <jats:bold> Bakulin <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="1340" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1217745">1340</jats:related-article> , published online 23 February) studied a process in which the excitons created with an optical pulse were also subjected to infrared pulses. In polymer-blend devices, a three-step process was observed: The boundstate excitons diffused toward the donor-acceptor interface, formed a charge-transfer state, and then dissociated into free carriers. </jats:p>

<jats:title>Invading a Place Like Home</jats:title> <jats:p> Biological invasions can cause enormous economic problems but they also represent a biological experiment and provide insight into species distributions and range expansion or restriction. Most predictions about when and where species will invade rest on the assumption that invasive species will retain the same climatic niche in the invaded area. But is this assumption valid? <jats:bold> Petitpierre <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="1344" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215933">1344</jats:related-article> ) studied a large data set on plant invasions between Eurasia, North America, and Australia and indeed found that fewer than 15% of the studied species occupied more than 10% of invaded distribution outside their native climatic niche, and only one species exhibited &gt;50% climatic niche expansion in its invaded range. Thus, niche shifts are rather rare events in plant invasions. </jats:p>

<jats:title>Making Carlactone</jats:title> <jats:p> Germination of parasitic witchweeds depends on strigolactones, which also regulate plant branching and signal in the context of mycorrhizal symbioses. The biosynthetic pathways that lead to strigolactones are founded in carotenoid biosynthesis, but further steps have been obscure. <jats:bold> Alder <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="1348" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1218094">1348</jats:related-article> ) have now identified a biochemical pathway that generates a strigolactone-like compound, carlactone, which shows biological actions similar to those of strigolactone. </jats:p>

<jats:title>Toward Addiction</jats:title> <jats:p> Addiction can result when substances, such as drugs or alcohol, co-opt the brain's natural reward system. <jats:bold> Shohat-Ophir <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="1351" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215932">1351</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="6074" page="1309" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1220225">Zars</jats:related-article> </jats:bold> ) explored this potential in <jats:italic>Drosophila</jats:italic> by examining the relationship between the natural reward stimulated by mating and the unnatural reward offered by ethanol consumption. Males deprived of mating increased consumption of ethanol, and, when permitted to mate following deprivation, their ethanol consumption decreased. At a mechanistic level, mating increased the neurotransmitter neuropeptide F (NPF), while mate deprivation decreased NPF levels. </jats:p>

<jats:title>Facilitating Fusion and Release</jats:title> <jats:p> For neurotransmitters to be released from a neuron, a synaptic vesicle must fuse with the plasma membrane and form a fusion pore. Soluble <jats:italic>N</jats:italic> -ethylmaleimide–sensitive factor attachment protein receptor (SNARE) complexes are the core protein machinery involved in fusion; however, there has been debate regarding the mechanism. While in vitro studies have found that a single SNARE can cause fusion of two bilayers, in vivo studies have shown that a minimum of three SNAREs are required for neurotransmitter release. The apparently contradictory results are explained by <jats:bold> Shi <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="1355" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1214984">1355</jats:related-article> ), who monitored fusion of vesicles to membrane nanodiscs. While a single SNARE complex was sufficient to fuse bilayers, a minimum of three SNARE complexes were required to open a pore large enough for neurotransmitter release. </jats:p>

<jats:title>A Fair COP</jats:title> <jats:p> During eukaryotic intracellular membrane traffic, how is membrane curvature imparted by the cytoplasmic proteins that form the COPII coat, which mediates vesicle budding from the endoplasmic reticulum? <jats:bold> Čopič <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="1359" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215909">1359</jats:related-article> , published online 2 February; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6074" page="1308" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1220221">Silvius</jats:related-article> </jats:bold> ) dissected this process by exploiting yeast bypass-of-sec-thirteen ( <jats:italic>bst</jats:italic> ) mutants, which can survive without the otherwise essential COPII coat protein. These <jats:italic>bst</jats:italic> mutants appear to create a locally altered membrane that is more amenable to deformation by a Sec13-free coat. </jats:p>

<jats:title>A Synaptic Vesicle in Time</jats:title> <jats:p> Synaptic vesicles move extensively within presynaptic nerve terminals, and their positional features are thought to have an impact on the likelihood and mode of vesicle fusion and transmitter release. <jats:bold> Park <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="1362" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1216937">1362</jats:related-article> , published online 16 February) now provide real-time, three-dimensional tracking of individual synaptic vesicles in living nerve terminals. Single synaptic vesicles were identified within hippocampal neurons right up to the moment of exocytosis. </jats:p>

<jats:title>Ribosome Rescue</jats:title> <jats:p> Ribosomes stall when they reach the end of defective messenger RNAs (mRNAs). In bacteria, the most-studied ribosomal rescue pathway involves a ribonucleoprotein complex comprising tmRNA (which acts as both transfer RNA and mRNA) and the protein SmpB. In an alternative pathway, some Gram-negative bacteria contain proteins that achieve tmRNA-independent rescue. Now, <jats:bold> Neubauer <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="1366" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1217039">1366</jats:related-article> ) present the structure of the <jats:italic>Thermus thermophilus</jats:italic> ribosome bound to a fragment of tmRNA, SmpB, and elongation factor Tu, and <jats:bold> Gagnon <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="1370" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1217443">1370</jats:related-article> ) report the structure of the <jats:italic>T. thermophilus</jats:italic> ribosome in complex with an initiator tRNA, a short mRNA fragment, and the rescue factor YaeJ. Though the two rescue systems are very different, both involve a protein tail that binds in the mRNA channel. This orients the rescue apparatus to facilitate switching translation to a different message in the tmRNA system or hydrolysis of peptidyl tRNA by YaeJ. </jats:p>