Catálogo de publicaciones - revistas

<jats:p>Ocean oil slicks can be attributed to natural seepages or to anthropogenic discharges. To date, the global picture of their distribution and relative natural and anthropogenic contributions remains unclear. Here, by analyzing 563,705 Sentinel-1 images from 2014–2019, we provide the first global map of oil slicks and a detailed inventory of static-and-persistent sources (natural seeps, platforms, and pipelines). About 90% of oil slicks were within 160 kilometers of shorelines, with 21 high-density slick belts coinciding well with shipping routes. Quantified by slick area, the proportion of anthropogenic discharges was an order of magnitude greater than natural seepages (94 versus 6%), in contrast to the previous estimate quantified by volume during 1990–1999 (54 versus 46%). Our findings reveal that the present-day anthropogenic contribution to marine oil pollution may have been substantially underestimated.</jats:p>

<jats:p>Ultracold atoms confined to periodic potentials have proven to be a powerful tool for quantum simulation of complex many-body systems. We confine fermions to one dimension to realize the Tomonaga-Luttinger liquid model, which describes the highly collective nature of their low-energy excitations. We use Bragg spectroscopy to directly excite either the spin or charge waves for various strengths of repulsive interaction. We observe that the velocity of the spin and charge excitations shift in opposite directions with increasing interaction, a hallmark of spin-charge separation. The excitation spectra are in quantitative agreement with the exact solution of the Yang-Gaudin model and the Tomonaga-Luttinger liquid theory. Furthermore, we identify effects of nonlinear corrections to this theory that arise from band curvature and back-scattering.</jats:p>

<jats:p> Erbium-doped fiber amplifiers revolutionized long-haul optical communications and laser technology. Erbium ions could provide a basis for efficient optical amplification in photonic integrated circuits but their use remains impractical as a result of insufficient output power. We demonstrate a photonic integrated circuit–based erbium amplifier reaching 145 milliwatts of output power and more than 30 decibels of small-signal gain—on par with commercial fiber amplifiers and surpassing state-of-the-art III-V heterogeneously integrated semiconductor amplifiers. We apply ion implantation to ultralow–loss silicon nitride (Si <jats:sub>3</jats:sub> N <jats:sub>4</jats:sub> ) photonic integrated circuits, which are able to increase the soliton microcomb output power by 100 times, achieving power requirements for low-noise photonic microwave generation and wavelength-division multiplexing optical communications. Endowing Si <jats:sub>3</jats:sub> N <jats:sub>4</jats:sub> photonic integrated circuits with gain enables the miniaturization of various fiber-based devices such as high–pulse-energy femtosecond mode-locked lasers. </jats:p>

<jats:p>In eukaryotes, RNA polymerase (Pol) II transcribes chromatin and must move past nucleosomes, often resulting in nucleosome displacement. How Pol II unwraps the DNA from nucleosomes to allow transcription and how DNA rewraps to retain nucleosomes has been unclear. Here, we report the 3.0-angstrom cryo–electron microscopy structure of a mammalian Pol II-DSIF-SPT6-PAF1c-TFIIS-nucleosome complex stalled 54 base pairs within the nucleosome. The structure provides a mechanistic basis for nucleosome retention during transcription elongation where upstream DNA emerging from the Pol II cleft has rewrapped the proximal side of the nucleosome. The structure uncovers a direct role for Pol II and transcription elongation factors in nucleosome retention and explains how nucleosomes are retained to prevent the disruption of chromatin structure across actively transcribed genes.</jats:p>

<jats:p>In Arabia, the first half of the sixth century CE was marked by the demise of Himyar, the dominant power in Arabia until 525 CE. Important social and political changes followed, which promoted the disintegration of the major Arabian polities. Here, we present hydroclimate records from around Southern Arabia, including a new high-resolution stalagmite record from northern Oman. These records clearly indicate unprecedented droughts during the sixth century CE, with the most severe aridity persisting between ~500 and 530 CE. We suggest that such droughts undermined the resilience of Himyar and thereby contributed to the societal changes from which Islam emerged.</jats:p>

<jats:p>The emergence of new therapeutic modalities requires complementary tools for their efficient syntheses. Availability of methodologies for site-selective modification of biomolecules remains a long-standing challenge, given the inherent complexity and the presence of repeating residues that bear functional groups with similar reactivity profiles. We describe a bioconjugation strategy for modification of native peptides relying on high site selectivity conveyed by enzymes. We engineered penicillin G acylases to distinguish among free amino moieties of insulin (two at amino termini and an internal lysine) and manipulate cleavable phenylacetamide groups in a programmable manner to form protected insulin derivatives. This enables selective and specific chemical ligation to synthesize homogeneous bioconjugates, improving yield and purity compared to the existing methods, and generally opens avenues in the functionalization of native proteins to access biological probes or drugs.</jats:p>

<jats:p> Repeated emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with increased fitness underscores the value of rapid detection and characterization of new lineages. We have developed PyR <jats:sub>0</jats:sub> , a hierarchical Bayesian multinomial logistic regression model that infers relative prevalence of all viral lineages across geographic regions, detects lineages increasing in prevalence, and identifies mutations relevant to fitness. Applying PyR <jats:sub>0</jats:sub> to all publicly available SARS-CoV-2 genomes, we identify numerous substitutions that increase fitness, including previously identified spike mutations and many nonspike mutations within the nucleocapsid and nonstructural proteins. PyR <jats:sub>0</jats:sub> forecasts growth of new lineages from their mutational profile, ranks the fitness of lineages as new sequences become available, and prioritizes mutations of biological and public health concern for functional characterization. </jats:p>

<jats:p>Polar bears are susceptible to climate warming because of their dependence on sea ice, which is declining rapidly. We present the first evidence for a genetically distinct and functionally isolated group of polar bears in Southeast Greenland. These bears occupy sea-ice conditions resembling those projected for the High Arctic in the late 21st century, with an annual ice-free period that is &gt;100 days longer than the estimated fasting threshold for the species. Whereas polar bears in most of the Arctic depend on annual sea ice to catch seals, Southeast Greenland bears have a year-round hunting platform in the form of freshwater glacial mélange. This suggests that marine-terminating glaciers, although of limited availability, may serve as previously unrecognized climate refugia. Conservation of Southeast Greenland polar bears, which meet criteria for recognition as the world’s 20th polar bear subpopulation, is necessary to preserve the genetic diversity and evolutionary potential of the species.</jats:p>

<jats:p> The elongation of eukaryotic selenoproteins relies on a poorly understood process of interpreting in-frame UGA stop codons as selenocysteine (Sec). We used cryo-electron microscopy to visualize Sec UGA recoding in mammals. A complex between the noncoding Sec-insertion sequence (SECIS), SECIS-binding protein 2 (SBP2), and 40 <jats:italic>S</jats:italic> ribosomal subunit enables Sec-specific elongation factor eEFSec to deliver Sec. eEFSec and SBP2 do not interact directly but rather deploy their carboxyl-terminal domains to engage with the opposite ends of the SECIS. By using its Lys-rich and carboxyl-terminal segments, the ribosomal protein eS31 simultaneously interacts with Sec-specific transfer RNA (tRNA <jats:sup>Sec</jats:sup> ) and SBP2, which further stabilizes the assembly. eEFSec is indiscriminate toward <jats:sc>l</jats:sc> -serine and facilitates its misincorporation at Sec UGA codons. Our results support a fundamentally distinct mechanism of Sec UGA recoding in eukaryotes from that in bacteria. </jats:p>

<jats:p> Effective tissue repair after myocardial infarction entails a vigorous angiogenic response, guided by incompletely defined immune cell–endothelial cell interactions. We identify the monocyte- and macrophage-derived cytokine METRNL (meteorin-like) as a driver of postinfarction angiogenesis and high-affinity ligand for the stem cell factor receptor KIT (KIT receptor tyrosine kinase). METRNL mediated angiogenic effects in cultured human endothelial cells through KIT-dependent signaling pathways. In a mouse model of myocardial infarction, METRNL promoted infarct repair by selectively expanding the KIT-expressing endothelial cell population in the infarct border zone. <jats:italic>Metrnl</jats:italic> -deficient mice failed to mount this KIT-dependent angiogenic response and developed severe postinfarction heart failure. Our data establish METRNL as a KIT receptor ligand in the context of ischemic tissue repair. </jats:p>