Catálogo de publicaciones - revistas

<jats:title>A Palladium 1–2 Punch</jats:title> <jats:p> Methods to replace carbon-hydrogen bonds directly with carbon-carbon bonds offer enticing prospects for streamlining the synthesis of organic compounds. The trouble is that it is hard to select any particular C-H bond and to avoid making complex mixtures of products. <jats:bold> He <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="6176" page="1216" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249198">1216</jats:related-article> ) report that a pair of powerful pyrimidine ligands induces a palladium catalyst to add aryl groups selectively to amino acid derivatives. One ligand promotes addition of a single aryl group to the β-carbon center; the other appends a second, potentially different aryl group to the same carbon—all in the same flask. </jats:p>

<jats:title>Clearance of Chronic Virus</jats:title> <jats:p> The family of mRNA-editing enzymes, APOBEC, restricts hepatitis B virus (HBV) replication. <jats:bold> Lucifora <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="6176" page="1221" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1243462">1221</jats:related-article> , published online 20 February; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6176" page="1212" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1252186"> <jats:bold>Shlomai and Rice</jats:bold> </jats:related-article> ) provide evidence that specific APOBECs mediate the anti-HBV effects of host cytokines, which in turn apparently induce nuclear deaminase activity without damaging host cells. Thus, there may be potential in these findings for developing a therapeutic route to curing chronic HBV infection. </jats:p>

<jats:title>Iron in Graphene</jats:title> <jats:p> Carbon or other covalently bonded materials, like boron nitride, can form two-dimensional sheets because of the strong bonding between the atoms. In contrast, metals share electrons in a three-dimensional delocalized way, and this could preclude the formation of thin stable sheets. Nevertheless, <jats:bold> Zhao <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="6176" page="1228" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1245273">1228</jats:related-article> ) observed pure iron membranes suspended across the pores in a graphene sheet. This phenomenon was discovered when an iron chloride solution, used to process the graphene, decomposed to form pure iron films across the pores. </jats:p>

<jats:title>Light Alkanes, Heavy Metals</jats:title> <jats:p> Hydraulic fracturing, or fracking, has rapidly increased the supply of natural gas and has motivated methods to convert its constituents into commodity chemicals. <jats:bold> Hashiguchi <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="6176" page="1232" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249357">1232</jats:related-article> ) have found that lead and thallium salts are both efficient and selective oxidants, not only for methane, but for ethane and propane as well. In trifluoroacetic acid solvent, the alkanes are cleanly oxidized to the trifluoroacetate esters of their respective alcohols and 1,2-diols. Building on earlier discoveries, this work paves the way to developing methods that reduce our dependence on petroleum for industrial feedstocks. </jats:p>

<jats:title>G Below Sea</jats:title> <jats:p> Rheological differences between Earth's lithosphere and asthenosphere help drive plate tectonics. Geophysical analyses repeatedly reveal a seismic Gutenberg (G) discontinuity at 40- to 100-kilometer depth in oceanic plates, although the origin of this boundary remains enigmatic. <jats:bold> Beghein <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="6176" page="1237" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1246724">1237</jats:related-article> , published online 27 February) found that vertical stratification of anisotropy aligned with the depths of the G discontinuity, but not with the lithosphere-asthenosphere boundary. It appears that the G discontinuity forms when there are geophysical changes in the mantle, such as dehydration beneath mid-ocean ridges. </jats:p>

<jats:title>Hidden Diversity</jats:title> <jats:p> Why are there so many species in the tropics? Niche partitioning by highly specialized plant species seems to be the main generator of high diversity. <jats:bold> Condon <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="6176" page="1240" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1245007">1240</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="6176" page="1213" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1251275">Godfray</jats:related-article> </jats:bold> ) show that niche partitioning can also be generated by interactions between plant resources and parasites, resulting in hyperdiverse communities. The cryptic diversity of 14 neotropical fly pollinators and 18 of their highly specific wasp parasites induced mortality partitions between multiple narrow niches. The extreme specificity of the wasp-fly relationships was initially only revealed by molecular analysis. </jats:p>

<jats:title>Crossed Homodimer</jats:title> <jats:p> Our cells respond to infection by releasing interferons, which protect neighboring cells, in part through the cleavage of intracellular RNA by a protein kinase family receptor, RNase L. RNase L is activated by 2′,5″-linked oligoadenylates (the second messenger 2-5 A), sensors of pathogen- and damage-associated RNA. <jats:bold> Han <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="6176" page="1244" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249845">1244</jats:related-article> , published online 27 February) report crystal structures of human RNase L in complexes with 2-5 A, nucleotides, and an 18-nucleotide oligomer RNA target. </jats:p>

<jats:title>Making a Histone Mark</jats:title> <jats:p> The covalent marks on histones (the principal components of chromatin) play a critical role in the regulation of gene expression. Somehow these marks are preserved when a cell in a tissue divides so that the daughter cells maintain the gene expression program and tissue identity of the parent cell. <jats:bold> Jacob <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="6176" page="1249" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248357">1249</jats:related-article> ) show that the <jats:italic>Arabidopsis</jats:italic> histone methylase ATXR5 is specific for the replication-dependent histone variant H3.1 and maintains the repressive histone H3 lysine-27 methyl mark on the H3.1 variant during genome replication, thus, preserving cell-type–specific regions of heterochromatin and gene repression through cell division and beyond. </jats:p>

<jats:title>Where Do You Want Your Leg?</jats:title> <jats:p> Initiation of limb formation is the key to understanding limb-cell specification and patterning during development. <jats:bold>Gros and Tabin</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6176" page="1253" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248228">1253</jats:related-article> ) show that a localized epithelial-to-mesenchymal transition triggers the formation of the limb. Finding that limbs initiate through cell-state change, and not through differential proliferation, redefines questions such as how limb buds are placed on the body plan. </jats:p>

<jats:title>Touchy-Feely Genes</jats:title> <jats:p> All animals need accurate proprioceptive sensation to control motor function. <jats:bold> Desai <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="6176" page="1256" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1247761">1256</jats:related-article> ) identified a <jats:italic>Drosophila</jats:italic> mutant with impaired walking coordination. The affected gene, <jats:italic>stumble</jats:italic> ( <jats:italic>stum</jats:italic> ), is conserved throughout the animal kingdom and expressed in a subpopulation of multidendritic neurons. <jats:italic>stum</jats:italic> -expressing neurons are found proximal to leg joints, and if the angle of the joint shifts, dendritic stretching occurs that in turn elevates cellular calcium. Therefore, it looks as if <jats:italic>stum</jats:italic> is a transducer for mechanical stimuli. </jats:p>