Catálogo de publicaciones - revistas

<jats:title>Codifying Maize Modifications</jats:title> <jats:p> Maize, one of our most important crop species, has been the target of genetic investigation and experimentation for more than 100 years. Crossing two inbred lines tends to result in “better” offspring, in a process known as heterosis. Attempts to map the genetic loci that control traits important for farming have been made, but few have been successful (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5941" page="688" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178420">Mackay</jats:related-article> </jats:bold> ). <jats:bold> Buckler <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="714" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174276">714</jats:related-article> ) and <jats:bold> McMullen <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="737" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174320">737</jats:related-article> ) produced a genomic map of maize that relates recombination to genome structure. Even tremendous adaptations in very diverse species were produced by numerous, small additive steps. Differences in flowering time in maize among inbred lines were not caused by a few genes with large effects, but by the cumulative effects of numerous quantitative trait loci—each of which has only a small impact on the trait. </jats:p>

<jats:title>Cosmic Shock Waves</jats:title> <jats:p> Cosmic rays are high-energy charged particles that bombard Earth from all directions in the sky; those originating from within our Galaxy are thought to be accelerated in the shockwaves produced by supernova explosions. <jats:bold> Helder <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="719" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173383">719</jats:related-article> , published online 25 June; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5941" page="683" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1177743">Raymond</jats:related-article> </jats:bold> ) measured the velocity of a section of the blast wave created by supernova RCW 86, an exploding star believed to have been witnessed by Chinese astronomers in 185 A.D., and the post-shock proton temperature. The post-shock proton temperature was much lower than would be expected without any cosmic ray acceleration, which implies that the pressure induced by cosmic ray exceeds the thermal pressure behind the shock. </jats:p>

<jats:title>Higher-Level Quantum Emulation</jats:title> <jats:p> At the heart of a quantum computer is the device on which information is to be encoded. This is typically done with a qubit, a two-level quantum system analogous to the two-level bit that encodes 0 and 1 in classical computers. However, there need not be just two quantum energy levels. There could be three (a qutrit), or more generally, <jats:italic>d</jats:italic> -levels (a qudit) in the device. <jats:bold> Neeley <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="722" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173440">722</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="5941" page="689" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178828">Nori</jats:related-article> </jats:bold> ) demonstrate a five-level quantum device and show that their qudit can be used to emulate the processes involved in manipulating quantum spin. The use of multilevel qudits may also have potential in quantum information processing by simplifying certain computational tasks and simplifying the circuitry required to realize the quantum computer itself. </jats:p>

<jats:title>Stressful Self-Assembly</jats:title> <jats:p> One way to control shape during the assembly of an object is to design in stresses that cause a planned amount of deformation. <jats:bold> Dietz <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="725" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174251">725</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="5941" page="685" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178328">Liu and Yan</jats:related-article> </jats:bold> ) designed DNA helix bundles, arranged in honeycomb lattices, in which some of the helices have insertions or deletions relative to the other helices in the bundles. The stresses help the bundles assemble into objects on the scale of tens of nanometers. Both the direction and degree of bending could be controlled, and curvatures as tight as 6 nanometers achieved. Complex shapes, such as square-toothed gears, could be created by combining multiple curved elements. </jats:p>

<jats:title>No NO</jats:title> <jats:p> Isoprene, a five-carbon diene produced by plants, is the most abundant nonmethane hydrocarbon released into the atmosphere and plays an important role in tropospheric chemistry. Isoprene is also thought to affect climate by acting as a source of atmospheric aerosols. <jats:bold> Paulot <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="730" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1172910">730</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="5941" page="687" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178324">Kleindienst</jats:related-article> </jats:bold> ) now describe how isoprene may lead to the formation of secondary organic aerosols. In laboratory experiments, the photooxidation of isoprene in low-NO conditions, such as those which occur in vegetated regions far from anthropogenic influence, produced high yields of dihydroxy epoxides, a suspected precursor of the aerosols. This discovery could help to explain some of the more puzzling aspects of isoprene chemistry in remote regions. </jats:p>

<jats:title>Honing Bivalve History</jats:title> <jats:p> What are the lasting effects of extinction, both persistent background extinctions and major events, on surviving lineages? <jats:bold> Roy <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="733" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173073">733</jats:related-article> ) examined the excellent fossil record of marine bivalves over the past 200 million years, which spans the end-Cretaceous extinction. Background extinctions tended to be higher within certain lineages and depended on the previous history of extinctions within those lineages. Cenozoic taxa are still reflecting the end-Cretaceous event. </jats:p>

<jats:title>Codifying Maize Modifications</jats:title> <jats:p> Maize, one of our most important crop species, has been the target of genetic investigation and experimentation for more than 100 years. Crossing two inbred lines tends to result in “better” offspring, in a process known as heterosis. Attempts to map the genetic loci that control traits important for farming have been made, but few have been successful (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5941" page="688" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178420">Mackay</jats:related-article> </jats:bold> ). <jats:bold> Buckler <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="714" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174276">714</jats:related-article> ) and <jats:bold> McMullen <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="737" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174320">737</jats:related-article> ) produced a genomic map of maize that relates recombination to genome structure. Even tremendous adaptations in very diverse species were produced by numerous, small additive steps. Differences in flowering time in maize among inbred lines were not caused by a few genes with large effects, but by the cumulative effects of numerous quantitative trait loci—each of which has only a small impact on the trait. </jats:p>

<jats:title>&lt;&lt; Focusing on Fibrin</jats:title> <jats:p> Vascular injury initiates biochemical reactions that cause the blood protein, fibrin, to polymerize and help to stop bleeding and support wound healing. Fibrin can also be a scaffold for thrombi that lead to cardiovascular diseases. To maintain homeostasis, fibrin clots must be stiff, plastic, and, so that the network can be decompsed, permeable. <jats:bold> Brown <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="741" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1172484">741</jats:related-article> ) investigated the behavior of fibrin clots at the macroscopic, single-fiber, and molecular scale. At relatively low strains, fibers aligned and formed bundles, and at higher strains, protein unfolding occurred. An integrated model provides a molecular basis for fibrin elasticity and extensibility. </jats:p>

<jats:title>Transfer RNA Fix</jats:title> <jats:p> Accurate protein synthesis requires that transfer RNAs (tRNAs) must be acylated with the correct amino acid. Mistranslation of serine or glycine for alanine apparently presents a particular challenge and is corrected by an editing domain of alanyl-tRNA synthetases (AlaRSs). <jats:bold> Guo <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="744" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174343">744</jats:related-article> ) now show that aside from the aminoacylation and editing domains, a third domain, C-Ala, plays a key role in AlaRS function. It forms a nucleic acid–binding motif that promotes binding of both aminoacylation and editing domains to tRNA <jats:sup>Ala</jats:sup> . The coupling of these two functions was likely important in the evolution of AlaRSs. </jats:p>

<jats:title>Untangling Food Webs</jats:title> <jats:p> The factors affecting the stability of food webs are important in conservation and ecological restoration. <jats:bold> Gross <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="747" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173536">747</jats:related-article> ) used a generalized modeling approach to evaluate billions of replicates of food webs in order to reveal the properties that stabilize (or destabilize) food webs. Variability in the strength of trophic links between predator and prey strength affected stability in different ways depending on the size of the web—stabilizing only in relatively small food webs and destabilizing in larger ones. Universal topological rules were extracted for the patterns of network links that enhance food-web stability. </jats:p>