Catálogo de publicaciones - revistas

<jats:title>Gas flows and disks in a young binary</jats:title> <jats:p> Many stars are in binary systems, pairs of stars gravitationally bound to each other, often with the two components having similar masses. It remains unclear how these systems assemble and accrete material. Alves <jats:italic>et al.</jats:italic> made high-resolution observations of a young binary star that is still in the process of forming. A large disk surrounds both stars, and each component also has its own smaller circumstellar disk. Spiral filaments of dust and gas connect the small disks to the larger one. Material is accreting preferentially onto the star that currently has a lower mass, driving the masses toward similar values. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="90" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aaw3491">90</jats:related-article> </jats:p>

<jats:title>Building up an optical clock</jats:title> <jats:p> Arrays of optical tweezers can be used to trap atoms, which can then be manipulated individually. Such arrays have shown promise in quantum simulation of many-body systems. Norcia <jats:italic>et al.</jats:italic> now demonstrate that they can also be used as a platform for optical clocks. The researchers lined up 10 optical tweezers in a one-dimensional array, where each tweezer held either one or zero atoms of strontium. The atoms were subjected to laser light whose frequency was tuned to a clock transition in strontium. By monitoring the number of atoms in each tweezer, the researchers measured a long coherence time of a few seconds. Increasing the number of tweezers should improve the figures of merit of this platform. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="93" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aay0644">93</jats:related-article> </jats:p>

<jats:title>Glowing filaments of the cosmic web</jats:title> <jats:p> Most gas in the Universe lies in the intergalactic medium, where it forms into sheets and filaments of the cosmic web. Clusters of galaxies form at the intersection of these filaments, fed by gas pulled along them by gravity. Although this picture is well established by cosmological simulations, it has been difficult to demonstrate observationally. Umehata <jats:italic>et al.</jats:italic> mapped emission from the intergalactic medium in an area around galaxies that are starting to form a cluster (see the Perspective by Hamden). They found that the gas is arranged into filaments, whose position and velocity correlate with star-forming galaxies, supporting the theoretical picture. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="97" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aaw5949">97</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="31" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aaz1318">31</jats:related-article> </jats:p>

<jats:title>Hemes switch spots in a terminal oxidase</jats:title> <jats:p> Reduction of molecular oxygen to water is the driving force for respiration in aerobic organisms and is catalyzed by several distinct integral membrane complexes. These include an exclusively prokaryotic enzyme, cytochrome bd–type quinol oxidase, which is a potential antimicrobial target. Safarian <jats:italic>et al.</jats:italic> determined a high-resolution cryo–electron microscopy structure of this enzyme from the enteric bacterium <jats:italic>Escherichia coli</jats:italic> . Comparison to a homolog reveals a complete relocation of the site of oxygen binding and reduction caused by a change in the arrangement of heme cofactors and channels in the protein scaffold. This switch illustrates the diversity of structure and function in this family of enzymes and might reflect different biochemical roles of these homologs. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="100" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aay0967">100</jats:related-article> </jats:p>

<jats:title>Speeding up submicrometer printing</jats:title> <jats:p> Using light to build three-dimensional structures with photopolymerization is the basis for two-photon lithography. However, there has been a trade-off between speed and resolution for fabricating structures with this method. Saha <jats:italic>et al.</jats:italic> optimize a new parallel printing methodology that relies on ultrafast lasers. They show the ability to dramatically increase the speed of printing while maintaining submicrometer resolution. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="105" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aax8760">105</jats:related-article> </jats:p>

<jats:title>The yin and yang of Raf inhibition</jats:title> <jats:p> Many human melanomas contain an overactive form of Raf kinase (B-Raf). Inhibitors are effective against the mutant B-Raf, but, paradoxically, they activate wild-type B-Raf, limiting their therapeutic potential. Kondo <jats:italic>et al.</jats:italic> determined the structure of a phosphorylated B-Raf dimer in complex with the scaffold protein 14-3-3 by cryo–electron microscopy. Although both kinases are in the active conformation, one is blocked by the C-terminal tail of the other. This configuration inhibits one active site but also stabilizes the dimer in the active conformation. Understanding this mechanism provides a framework for development of inhibitors that do not activate wild-type Raf. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="109" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aay0543">109</jats:related-article> </jats:p>

<jats:title>Protein competition drives cell fate</jats:title> <jats:p> Cell survival can require switching mechanisms that are flexible enough to accommodate environmental changes but also stable for the required duration. Lord <jats:italic>et al.</jats:italic> created a switching system in bacteria based on stochastic competition between two proteins: one is a transcriptional repressor, and the other is an antagonist that binds the repressor and locks it in an inactive state. They show that this system controls switching of the bacterium <jats:italic>Bacillus subtilis</jats:italic> from a motile, unicellular state to an immobile, multicellular state, and that the control system is transferable to another distantly related bacterium. Similar mechanisms could be more widely operable in biological systems than previously recognized. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="116" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aaw4506">116</jats:related-article> </jats:p>

<jats:title>Staggering decline of bird populations</jats:title> <jats:p> Because birds are conspicuous and easy to identify and count, reliable records of their occurrence have been gathered over many decades in many parts of the world. Drawing on such data for North America, Rosenberg <jats:italic>et al.</jats:italic> report wide-spread population declines of birds over the past half-century, resulting in the cumulative loss of billions of breeding individuals across a wide range of species and habitats. They show that declines are not restricted to rare and threatened species—those once considered common and wide-spread are also diminished. These results have major implications for ecosystem integrity, the conservation of wildlife more broadly, and policies associated with the protection of birds and native ecosystems on which they depend. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="120" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aaw1313">120</jats:related-article> </jats:p>

<jats:title>Fungal influence on density dependence</jats:title> <jats:p> Tree species in highly diverse tropical forests tend to exhibit conspecific negative density dependence, a phenomenon whereby individuals of the same species tend to grow at a distance from one another. This is understood to be a key driver of species coexistence. The strength of negative density dependence varies between species, but the mechanisms driving this variation are unknown. Chen <jats:italic>et al.</jats:italic> studied tree species in a subtropical forest in China and found an important role for soil-dwelling fungi in this variation. Elevated accumulation of pathogenic fungi leads to stronger negative density dependence, whereas elevated accumulation of mutualistic fungi leads to weaker negative density dependence. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="124" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aau1361">124</jats:related-article> </jats:p>

<jats:title>Distant cousin helps spot animal enzyme</jats:title> <jats:p> In addition to forming the membranes that enclose cells, lipids are important signaling molecules. Plasmalogens, which contain a vinyl ether linkage, are an abundant group of lipids in animals. How these lipids are synthesized from precursors with an alkyl ether linkage has been a mystery. Gallego-García <jats:italic>et al.</jats:italic> found an enzyme, CarF, in the social bacterium <jats:italic>Myxococcus xanthus</jats:italic> that produces plasmalogens used in a signaling pathway for singlet oxygen, a marker of photooxidative stress. They then showed that the animal homolog could catalyze the final step in plasmalogen synthesis in bacterial and human cells, thus resolving a source for plasmalogens in animals. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6461" page="128" related-article-type="in-this-issue" vol="366" xlink:href="10.1126/science.aay1436">128</jats:related-article> </jats:p>