Catálogo de publicaciones - revistas

<jats:title>Converging on Dynamics</jats:title> <jats:p> Electron diffraction is a versatile technique for discerning atomic-level structure, but the data emerge averaged over the micron–scale area sampled by the electrons, and so blur local distinctions in systems that aren't strictly periodic. A recent approach to minimizing this problem has been to focus the electron beam impinging on the sample. <jats:bold>Yurtsever and Zewail</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="708" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1179314">708</jats:related-article> ) have now applied convergent focusing to an ultrafast electron diffraction apparatus and were thus able to resolve picosecond structural dynamics in local regions tens of nanometers across. The technique was used to probe heterogeneous temperature changes in laser-heated silicon. </jats:p>

<jats:title>Of Ancient Iron and Oxygen</jats:title> <jats:p> Finding clues to understand the early evolution of ocean and atmospheric chemistry and its links to the evolution of life remains a daunting task. Often just a few rock samples provide our only evidence of what conditions on Earth were like long ago. <jats:bold> Reinhard <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="713" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1176711">713</jats:related-article> ) combined iron speciation data from a 2.5-billion-year-old shale from Australia with sulfur isotope data from this and nearby formations to conclude that oxygen chemistry predominanty consisted of an anoxic sulfide–rich water column, instead of iron-rich oceans, as previously speculated. Thus, brief pulses of reduced iron from hydrothermal vents may have been responsible for the formation of nearby banded iron formations and may have provided enough buffering to prolong the appearance of atmospheric oxygen generated by the expansion of newly evolved cyanobacteria. </jats:p>

<jats:title>All Together Now</jats:title> <jats:p> Deciding how to change emissions of polluting gases that affect climate through their radiative forcing properties requires that the quantitative impact of these emissions be understood. Most past calculations of this type have considered only the radiative forcing of the specific emission and its atmospheric lifetime. <jats:bold> Shindell <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="716" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1174760">716</jats:related-article> ; see the Perspectives by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5953" page="672" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181568"> <jats:bold> Arneth <jats:italic>et al.</jats:italic> </jats:bold> </jats:related-article> </jats:bold> and by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5953" page="674" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1176064"> <jats:bold>Parrish and Zhu</jats:bold> </jats:related-article> </jats:bold> ) use sophisticated atmospheric chemical and climate modeling to determine how gas-aerosol interactions affect the radiative properties of the atmosphere, finding significant departures from the standard method for emissions of methane, carbon monoxide, and nitrogen oxides. These findings should help to optimize strategies for mitigating global warming by reducing anthropogenic emissions. </jats:p>

<jats:title>Iron Sensor</jats:title> <jats:p> Intracellular iron is an essential cofactor for many proteins, but can also damage macromolecules, so its levels are carefully controlled. Cellular iron homeostasis is mediated by iron regulatory proteins that regulate the expression of genes involved in iron uptake and storage. However, it is not clear how cells sense iron bioavailability (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5953" page="676" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181938">Rouault</jats:related-article> </jats:bold> ). Using different approaches, <jats:bold> Salahudeen <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="326" xlink:href="10.1126/science.1176326">722</jats:related-article> , published online 17 September) and <jats:bold> Vashisht <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="718" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1176333">718</jats:related-article> , published online 17 September) have identified the F-box protein FBXL5 as a human iron sensor. FBXL5 is part of an E3 ubiquitin ligase complex that regulates the degradation of iron regulatory proteins and thereby cellular iron levels. It contains a hemerythrin domain that binds iron and acts as an iron-dependent regulatory switch, causing the degradation of FBXL5 under low iron conditions. This alternative pathway for the regulation of iron homeostasis has implications for both normal cellular physiology and disease. </jats:p>

<jats:title>Iron Sensor</jats:title> <jats:p> Intracellular iron is an essential cofactor for many proteins, but can also damage macromolecules, so its levels are carefully controlled. Cellular iron homeostasis is mediated by iron regulatory proteins that regulate the expression of genes involved in iron uptake and storage. However, it is not clear how cells sense iron bioavailability (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5953" page="676" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181938">Rouault</jats:related-article> </jats:bold> ). Using different approaches, <jats:bold> Salahudeen <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="326" xlink:href="10.1126/science.1176326">722</jats:related-article> , published online 17 September) and <jats:bold> Vashisht <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="718" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1176333">718</jats:related-article> , published online 17 September) have identified the F-box protein FBXL5 as a human iron sensor. FBXL5 is part of an E3 ubiquitin ligase complex that regulates the degradation of iron regulatory proteins and thereby cellular iron levels. It contains a hemerythrin domain that binds iron and acts as an iron-dependent regulatory switch, causing the degradation of FBXL5 under low iron conditions. This alternative pathway for the regulation of iron homeostasis has implications for both normal cellular physiology and disease. </jats:p>

<jats:title>Flu's Tricky Tricks</jats:title> <jats:p> After vaccination against influenza A virus, single-point mutations are selected in hemagglutinin (the virus molecule that binds to sialic acid molecules on the surface of host cells) that escape neutralization by polyclonal antibody responses. <jats:bold> Hensley <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="734" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178258">734</jats:related-article> ) have discovered that in mice these mutations increased the virus's avidity for sialic acid. Amino acid substitutions that occur during reiterations of immune escape and avidity modulation can thus drive antigenic variation. This constant evolution of influenza viruses requires us to change vaccine components annually, and, for equine influenza, <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="726" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1175980">726</jats:related-article> ) show that as the match between virus and vaccine strains drifts apart with time, the probability of becoming infected and the length of the infectious period increase to the point where outbreaks occur. Nevertheless, even imperfect vaccines may be of benefit to a population because increasing the proportion of vaccinated individuals can supply enough herd immunity to offset a poor antigenic match, especially if used in conjunction with antiviral drugs. For humans, <jats:bold> Yang <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="729" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177373">729</jats:related-article> , published online 10 September) estimate that the rate of transmission within U.S. households puts influenza A 2009 H1N1 (the current pandemic “swine flu”) in the higher range of transmissibility, compared to past seasonal and pandemic strains. Thus, to achieve mitigation this fall, children should be the first recipients of vaccine, followed by adults—aiming overall for 70% coverage of the population. </jats:p>

<jats:title>Flu's Tricky Tricks</jats:title> <jats:p> After vaccination against influenza A virus, single-point mutations are selected in hemagglutinin (the virus molecule that binds to sialic acid molecules on the surface of host cells) that escape neutralization by polyclonal antibody responses. <jats:bold> Hensley <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="734" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178258">734</jats:related-article> ) have discovered that in mice these mutations increased the virus's avidity for sialic acid. Amino acid substitutions that occur during reiterations of immune escape and avidity modulation can thus drive antigenic variation. This constant evolution of influenza viruses requires us to change vaccine components annually, and, for equine influenza, <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="726" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1175980">726</jats:related-article> ) show that as the match between virus and vaccine strains drifts apart with time, the probability of becoming infected and the length of the infectious period increase to the point where outbreaks occur. Nevertheless, even imperfect vaccines may be of benefit to a population because increasing the proportion of vaccinated individuals can supply enough herd immunity to offset a poor antigenic match, especially if used in conjunction with antiviral drugs. For humans, <jats:bold> Yang <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="729" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177373">729</jats:related-article> , published online 10 September) estimate that the rate of transmission within U.S. households puts influenza A 2009 H1N1 (the current pandemic “swine flu”) in the higher range of transmissibility, compared to past seasonal and pandemic strains. Thus, to achieve mitigation this fall, children should be the first recipients of vaccine, followed by adults—aiming overall for 70% coverage of the population. </jats:p>

<jats:title>Flu's Tricky Tricks</jats:title> <jats:p> After vaccination against influenza A virus, single-point mutations are selected in hemagglutinin (the virus molecule that binds to sialic acid molecules on the surface of host cells) that escape neutralization by polyclonal antibody responses. <jats:bold> Hensley <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="734" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178258">734</jats:related-article> ) have discovered that in mice these mutations increased the virus's avidity for sialic acid. Amino acid substitutions that occur during reiterations of immune escape and avidity modulation can thus drive antigenic variation. This constant evolution of influenza viruses requires us to change vaccine components annually, and, for equine influenza, <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="726" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1175980">726</jats:related-article> ) show that as the match between virus and vaccine strains drifts apart with time, the probability of becoming infected and the length of the infectious period increase to the point where outbreaks occur. Nevertheless, even imperfect vaccines may be of benefit to a population because increasing the proportion of vaccinated individuals can supply enough herd immunity to offset a poor antigenic match, especially if used in conjunction with antiviral drugs. For humans, <jats:bold> Yang <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="729" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177373">729</jats:related-article> , published online 10 September) estimate that the rate of transmission within U.S. households puts influenza A 2009 H1N1 (the current pandemic “swine flu”) in the higher range of transmissibility, compared to past seasonal and pandemic strains. Thus, to achieve mitigation this fall, children should be the first recipients of vaccine, followed by adults—aiming overall for 70% coverage of the population. </jats:p>

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

<jats:p>The show includes pandemic H1N1 and the 2009 Hajj, the contribution of inherited wealth to economic inequality, and more.</jats:p>