Catálogo de publicaciones - revistas

<jats:title>It's knot what you know</jats:title> <jats:p> Why is it that some knots seem to hold tight while others readily slip apart? Patil <jats:italic>et al.</jats:italic> develop a theoretical analysis of the stability of knots and find links between topological parameters (twist charge, crossing numbers, handedness) and mechanical stability. The theory is confirmed using simulations and experiments on color-changing fibers that optically show localized stress differences in different parts of the knot as the two strands are pulled apart. The authors show why some common knots slip easily and untie, whereas others hold tight. </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="6473" page="71" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aaz0135">71</jats:related-article> </jats:p>

<jats:title>Electrostatics guide chromophore twist</jats:title> <jats:p> Photoisomerization—the twisting of bonds in a molecule in response to absorption of light—is exploited in biology to sense light and can influence the photophysical properties of fluorescent proteins used in imaging applications. Romei <jats:italic>et al.</jats:italic> studied this behavior by introducing unnatural amino acids into the photoswitchable green fluorescent protein Dronpa2, thus systematically altering the electronic properties of the chromophore (see the Perspective by Hu <jats:italic>et al.</jats:italic> ). Crystal structures and spectroscopic analyses of a series of these variants support a model in which the electrostatic interactions between the chromophore and its environment influence the barrier heights for twisting around different bonds during photoisomerization. These insights may guide future design of photoswitchable proteins with desired properties. </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="6473" page="76" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aax1898">76</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6473" page="26" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aba0571">26</jats:related-article> </jats:p>

<jats:title>Miniaturizing particle accelerators</jats:title> <jats:p> Particle accelerators are usually associated with large national facilities. Because photons are able to impart momentum to electrons, there are also efforts to develop laser-based particle accelerators. Sapra <jats:italic>et al.</jats:italic> developed an integrated particle accelerator using photonic inverse design methods to optimize the interaction between the light and the electrons. They show that an additional kick of around 0.9 kilo–electron volts (keV) can be given to a bunch of 80-keV electrons along just 30 micrometers of a specially designed channel. Such miniaturized dielectric laser accelerators could open up particle physics to a number of scientific disciplines. </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="6473" page="79" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aay5734">79</jats:related-article> </jats:p>

<jats:title>Human dendrites are special</jats:title> <jats:p> A special developmental program in the human brain drives the disproportionate thickening of cortical layer 2/3. This suggests that the expansion of layer 2/3, along with its numerous neurons and their large dendrites, may contribute to what makes us human. Gidon <jats:italic>et al.</jats:italic> thus investigated the dendritic physiology of layer 2/3 pyramidal neurons in slices taken from surgically resected brain tissue in epilepsy patients. Dual somatodendritic recordings revealed previously unknown classes of action potentials in the dendrites of these neurons, which make their activity far more complex than has been previously thought. These action potentials allow single neurons to solve two long-standing computational problems in neuroscience that were considered to require multilayer neural networks. </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="6473" page="83" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aax6239">83</jats:related-article> </jats:p>

<jats:title>Middle Stone Age cooking</jats:title> <jats:p> Early evidence of cooked starchy plant food is sparse, yet the consumption of starchy roots is likely to have been a key innovation in the human diet. Wadley <jats:italic>et al.</jats:italic> report the identification of whole, charred rhizomes of plants of the genus <jats:italic>Hypoxis</jats:italic> from Border Cave, South Africa, dated up to 170,000 years ago. These archaeobotanical remains represent the earliest direct evidence for the cooking of underground storage organs. The edible <jats:italic>Hypoxis</jats:italic> rhizomes appear to have been cooked and consumed in the cave by the Middle Stone Age humans at the site. <jats:italic>Hypoxis</jats:italic> has a wide geographical distribution, suggesting that the rhizomes could have been a ready and reliable carbohydrate source for <jats:italic>Homo sapiens</jats:italic> in Africa, perhaps facilitating the mobility of human populations. </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="6473" page="87" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aaz5926">87</jats:related-article> </jats:p>

<jats:title>Subtle origin for complex shapes</jats:title> <jats:p> The cup-shaped leaves of carnivorous plants have evolved multiple times from ancestors with flat leaves. Studying development of the carnivorous trap in the humped bladderwort, <jats:italic>Utricularia gibba</jats:italic> , Whitewoods <jats:italic>et al.</jats:italic> identified genes similar to those expressed in surfaces of flat leaves (see the Perspective by Moulton and Goriely). Ectopic expression and computational modeling reveals how slight shifts in gene expression domains make the difference between a flat leaf and a convoluted trap structure. Flexibility in growth rates in orthogonal polarity fields allows for diversity in shapes formed through development. </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="6473" page="91" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aay5433">91</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6473" page="24" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aba3797">24</jats:related-article> </jats:p>

<jats:title>Generating a new transcriptional network</jats:title> <jats:p> Organismal novelties result from changes in transcriptional circuits. But what comes first, changes in regulatory protein or changes in cis-regulatory sequences? Britton <jats:italic>et al.</jats:italic> examine the Matα2 protein in a Saccharomycotina clade of fungi. They show that a newly evolved transcription circuit involving repression of the a-specific genes by the ancient homeodomain protein Matα2 occurred in two stages separated by millions of years. In the first stage, Matα2 acquired several coding changes followed by changes in cis-regulatory sequences. This clade-specific requirement explains how the coding changes of Matα2 were in place long before the new a-specific gene repression circuit arose. </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="6473" page="96" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aax5217">96</jats:related-article> </jats:p>

<jats:title>Mechanism of tubulin autoregulation</jats:title> <jats:p> Cells tightly control the abundance of key housekeeping factors, such as ribosomes and chaperones, to maintain them at optimal levels needed for homeostasis. Most abundance control mechanisms involve feedback regulation of mRNA transcription, but others, such as tubulins, are regulated by highly specific mRNA degradation. Lin <jats:italic>et al.</jats:italic> found that tetratricopeptide protein 5 (TTC5) binds to nascent alpha and beta tubulins on translating ribosomes to trigger degradation of their associated mRNAs when excess tubulin is present (see the Perspective by Shoshani and Cleveland). In the absence of TTC5-mediated tubulin autoregulation, cells display error-prone chromosome segregation, a process critically dependent on tubulin concentration. </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="6473" page="100" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aaz4352">100</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6473" page="29" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aba0713">29</jats:related-article> </jats:p>

<jats:title>A possible propagating Majorana</jats:title> <jats:p> Majorana states in solid-state systems may one day form a basis for topological quantum computing. Most of the candidates identified so far have been Majorana bound states, but theorists have predicted that propagating Majorana states may exist as well. Wang <jats:italic>et al.</jats:italic> looked for such a state on the surface of the material FeSe <jats:sub>0.45</jats:sub> Te <jats:sub>0.55</jats:sub> (see the Perspective by Tewari and Stanescu). Using scanning tunneling spectroscopy, the researchers measured a flat, bias-independent density of states along a particular type of domain wall, which was consistent with a theoretical prediction for a propagating Majorana state in this material. Although topologically trivial origins of this finding are difficult to completely rule out, the work is likely to stimulate interest in iron-based superconductors as hosts of Majorana states. </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="6473" page="104" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aaw8419">104</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6473" page="23" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aaz6961">23</jats:related-article> </jats:p>

<jats:p>A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.</jats:p>