Catálogo de publicaciones - revistas

<jats:p>Through their association with a kleisin subunit (Scc1), cohesin’s Smc1 and Smc3 subunits are thought to form tripartite rings that mediate sister chromatid cohesion. Unlike the structure of Smc1/Smc3 and Smc1/Scc1 interfaces, that of Smc3/Scc1 is not known. Disconnection of this interface is thought to release cohesin from chromosomes in a process regulated by acetylation. We show here that the N-terminal domain of yeast Scc1 contains two α helices, forming a four-helix bundle with the coiled coil emerging from Smc3’s adenosine triphosphatase head. Mutations affecting this interaction compromise cohesin’s association with chromosomes. The interface is far from Smc3 residues, whose acetylation prevents cohesin’s dissociation from chromosomes. Cohesin complexes holding chromatids together in vivo do indeed have the configuration of hetero-trimeric rings, and sister DNAs are entrapped within these.</jats:p>

<jats:p>Chromosome segregation depends on sister chromatid cohesion mediated by cohesin. The cohesin subunits Smc1, Smc3, and Scc1 form tripartite rings that are thought to open at distinct sites to allow entry and exit of DNA. However, direct evidence for the existence of open forms of cohesin is lacking. We found that cohesin’s proposed DNA exit gate is formed by interactions between Scc1 and the coiled-coil region of Smc3. Mutation of this interface abolished cohesin’s ability to stably associate with chromatin and to mediate cohesion. Electron microscopy revealed that weakening of the Smc3-Scc1 interface resulted in opening of cohesin rings, as did proteolytic cleavage of Scc1. These open forms may resemble intermediate states of cohesin normally generated by the release factor Wapl and the protease separase, respectively.</jats:p>

<jats:p>Effective manipulation of cavity resonant modes is crucial for emission control in laser physics and applications. Using the concept of parity-time symmetry to exploit the interplay between gain and loss (i.e., light amplification and absorption), we demonstrate a parity-time symmetry–breaking laser with resonant modes that can be controlled at will. In contrast to conventional ring cavity lasers with multiple competing modes, our parity-time microring laser exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth. Thresholdless parity-time symmetry breaking due to the rotationally symmetric structure leads to stable single-mode operation with the selective whispering-gallery mode order. Exploration of parity-time symmetry in laser physics may open a door to next-generation optoelectronic devices for optical communications and computing.</jats:p>

<jats:p>The ability to control the modes oscillating within a laser resonator is of fundamental importance. In general, the presence of competing modes can be detrimental to beam quality and spectral purity, thus leading to spatial as well as temporal fluctuations in the emitted radiation. We show that by harnessing notions from parity-time (PT) symmetry, stable single–longitudinal mode operation can be readily achieved in a system of coupled microring lasers. The selective breaking of PT symmetry can be used to systematically enhance the maximum attainable output power in the desired mode. This versatile concept is inherently self-adapting and facilitates mode selectivity over a broad bandwidth without the need for other additional intricate components. Our experimental findings provide the possibility to develop synthetic optical devices and structures with enhanced functionality.</jats:p>

<jats:p>The Himalayan mountains are dissected by some of the deepest and most impressive gorges on Earth. Constraining the interplay between river incision and rock uplift is important for understanding tectonic deformation in this region. We report here the discovery of a deeply incised canyon of the Yarlung Tsangpo River, at the eastern end of the Himalaya, which is now buried under more than 500 meters of sediments. By reconstructing the former valley bottom and dating sediments at the base of the valley fill, we show that steepening of the Tsangpo Gorge started at about 2 million to 2.5 million years ago as a consequence of an increase in rock uplift rates. The high erosion rates within the gorge are therefore a direct consequence of rapid rock uplift.</jats:p>

<jats:p> Transit observations of HD 209458b in the stellar Lyman-α(Lyα) line revealed strong absorption in both blue and red wings of the line interpreted as hydrogen atoms escaping from the planet’s exosphere at high velocities. The following sources for the absorption were suggested: acceleration by the stellar radiation pressure, natural spectral line broadening, or charge exchange with the stellar wind. We reproduced the observation by means of modeling that includes all aforementioned processes. Our results support a stellar wind with a velocity of ≈400 kilometers per second at the time of the observation and a planetary magnetic moment of ≈1.6 × 10 <jats:sup>26</jats:sup> amperes per square meter. </jats:p>

<jats:p> Uranium dioxide (UO <jats:sub>2</jats:sub> ) is the major nuclear fuel component of fission power reactors. A key concern during severe accidents is the melting and leakage of radioactive UO <jats:sub>2</jats:sub> as it corrodes through its zirconium cladding and steel containment. Yet, the very high temperatures (&gt;3140 kelvin) and chemical reactivity of molten UO <jats:sub>2</jats:sub> have prevented structural studies. In this work, we combine laser heating, sample levitation, and synchrotron x-rays to obtain pair distribution function measurements of hot solid and molten UO <jats:sub>2</jats:sub> . The hot solid shows a substantial increase in oxygen disorder around the lambda transition (2670 K) but negligible U-O coordination change. On melting, the average U-O coordination drops from 8 to 6.7 ± 0.5. Molecular dynamics models refined to this structure predict higher U-U mobility than 8-coordinated melts. </jats:p>

<jats:p> Existing mouse models of lethal Ebola virus infection do not reproduce hallmark symptoms of Ebola hemorrhagic fever, neither delayed blood coagulation and disseminated intravascular coagulation nor death from shock, thus restricting pathogenesis studies to nonhuman primates. Here we show that mice from the Collaborative Cross panel of recombinant inbred mice exhibit distinct disease phenotypes after mouse-adapted Ebola virus infection. Phenotypes range from complete resistance to lethal disease to severe hemorrhagic fever characterized by prolonged coagulation times and 100% mortality. Inflammatory signaling was associated with vascular permeability and endothelial activation, and resistance to lethal infection arose by induction of lymphocyte differentiation and cellular adhesion, probably mediated by the susceptibility allele <jats:italic>Tek</jats:italic> . These data indicate that genetic background determines susceptibility to Ebola hemorrhagic fever. </jats:p>

<jats:p>The ongoing Ebola outbreak poses an alarming risk to the countries of West Africa and beyond. To assess the effectiveness of containment strategies, we developed a stochastic model of Ebola transmission between and within the general community, hospitals, and funerals, calibrated to incidence data from Liberia. We find that a combined approach of case isolation, contact-tracing with quarantine, and sanitary funeral practices must be implemented with utmost urgency in order to reverse the growth of the outbreak. As of 19 September, under status quo, our model predicts that the epidemic will continue to spread, generating a predicted 224 (134 to 358) daily cases by 1 December, 280 (184 to 441) by 15 December, and 348 (249 to 545) by 30 December.</jats:p>

<jats:p>We introduce the antibody landscape, a method for the quantitative analysis of antibody-mediated immunity to antigenically variable pathogens, achieved by accounting for antigenic variation among pathogen strains. We generated antibody landscapes to study immune profiles covering 43 years of influenza A/H3N2 virus evolution for 69 individuals monitored for infection over 6 years and for 225 individuals pre- and postvaccination. Upon infection and vaccination, titers increased broadly, including previously encountered viruses far beyond the extent of cross-reactivity observed after a primary infection. We explored implications for vaccination and found that the use of an antigenically advanced virus had the dual benefit of inducing antibodies against both advanced and previous antigenic clusters. These results indicate that preemptive vaccine updates may improve influenza vaccine efficacy in previously exposed individuals.</jats:p>