Catálogo de publicaciones - revistas

<jats:title>Upon reflection, modulate phase</jats:title> <jats:p> Metasurfaces provide a platform to fabricate optical devices in a compact form much thinner than their corresponding bulk optical components. Recognizing that metasurfaces are also open systems interacting with their environment, Song <jats:italic>et al</jats:italic> . designed a metasurface that exploits those non-Hermitian properties such that they can encircle an exceptional point. Subsequent scattering from such an exceptional point was shown to be polarization dependent, thus providing an additional control knob in designing metasurfaces for wave front engineering. —ISO </jats:p>

<jats:title>Linking flowering to ambient temperature</jats:title> <jats:p> In the small mustard plant <jats:italic>Arabidopsis</jats:italic> , the florigen FLOWERING LOCUS T (FT) mobilizes to initiate flowering at the shoot apical meristem. Susila <jats:italic>et al</jats:italic> . now show that FT, which is produced in leaf cells, can be held in reserve if ambient temperatures are not favorable (see the Perspective by Jaillais and Parcy). At low temperatures, FT binds a membrane phosopholipid and is thus restricted in mobility. At higher temperatures, such binding is less favored, and FT is released to mobilize into the shoot apical meristem to drive flowering. Thus, temperature-sensitive lipid binding helps the plant time flowering with favorable ambient temperatures. —PJH </jats:p>

<jats:title>A proofreader in SARS-CoV-2</jats:title> <jats:p> Although vaccines provide protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), there remains a need for antivirals to treat COVID-19. Nucleotide analog drugs such as remdesivir, which target the viral RNA polymerase, have potential but are compromised by exoribonuclease (ExoN) activity that removes incorrect nucleotides from newly synthesized RNA. Liu <jats:italic>et al</jats:italic> . determined the structure of the complex that harbors the ExoN activity (nsp10–nsp-14) bound to a mimic of RNA that has incorporated an incorrect nucleotide. The structure shows how the RNA is recognized and suggests how ExoN specifically removes mismatched nucleotides. It also provides clues for designing nucleotide analogs that may evade excision. —VV </jats:p>

<jats:title>Screen time for CRISPR</jats:title> <jats:p> CRISPR-Cas9 has been used to edit the genomes of organisms ranging from fruit flies to primates, but it has not been used in large-scale genetic screens in animals because generating, validating, and keeping track of large numbers of mutant animals is prohibitively laborious. Parvez <jats:italic>et al</jats:italic> . have developed Multiplexed Intermixed CRISPR Droplets, or MIC-Drop, a platform combining droplet microfluidics, en masse CRISPR injections, and barcoding, to enable large-scale genetic screens. In pilot phenotypic screens in zebrafish, MIC-Drop enabled rapid identification of the target of a small molecule and discovery of several new genes governing cardiovascular development. MIC-Drop is potentially scalable to thousands of targets and adaptable to diverse organisms and experiments. —DJ </jats:p>

<jats:title>Methanogenesis megacomplex</jats:title> <jats:p> An important first step in methanogenesis is the conversion of carbon dioxide to a reduced one-carbon formyl unit that is a substrate for downstream steps. This reaction is catalyzed by a complex of enzymes, including components for oxidizing hydrogen or formate and splitting two electrons along different energetic paths. Watanabe <jats:italic>et al</jats:italic> . carefully purified and prepared anaerobic cryo–electron microscopy samples of the enzyme complex responsible, resulting in a three-megadalton hexameric structure at 3- to 3.5-ångström resolution. The arrangement of iron–sulfur cofactors provides an explanation for how electron bifurcation is coupled to large protein motions, which are expected from the multiple conformational states present. —MAF </jats:p>

<jats:title>Defeating peripheral neuropathy</jats:title> <jats:p> The mechanisms underlying peripheral neuropathies are not well understood. Spaulding <jats:italic>et al</jats:italic> . studied mouse models of the inherited Charcot-Marie-Tooth (CMT) disease, which is caused by mutations in transfer RNA (tRNA) synthetases. Changes in gene expression and the rate of protein synthesis in neurons in the spinal cord triggered the cell stress response activated by the protein sensor GCN2. When GCN2 was genetically deleted or inhibited with drugs, the stress response was blocked, and the neuropathy was much milder. Zuko <jats:italic>et al</jats:italic> . found that mutant glycyl-tRNA synthetases bind tRNA <jats:sub>Gly</jats:sub> but fail to release it, thus depleting the cellular tRNA <jats:sub>Gly</jats:sub> pool. This process caused stalling of translating ribosomes on glycine codons and activated the integrated stress response. Transgenic tRNA <jats:sub>Gly</jats:sub> overexpression prevented peripheral neuropathy and protein synthesis defects in mouse and fruit fly models. Thus, elevating tRNA <jats:sub>Gly</jats:sub> levels or targeting GCN2 may have therapeutic potential for this currently untreatable disease (see the Perspective by Mellado and Willis). —SMH </jats:p>

<jats:title>Defeating peripheral neuropathy</jats:title> <jats:p> The mechanisms underlying peripheral neuropathies are not well understood. Spaulding <jats:italic>et al</jats:italic> . studied mouse models of the inherited Charcot-Marie-Tooth (CMT) disease, which is caused by mutations in transfer RNA (tRNA) synthetases. Changes in gene expression and the rate of protein synthesis in neurons in the spinal cord triggered the cell stress response activated by the protein sensor GCN2. When GCN2 was genetically deleted or inhibited with drugs, the stress response was blocked, and the neuropathy was much milder. Zuko <jats:italic>et al</jats:italic> . found that mutant glycyl-tRNA synthetases bind tRNA <jats:sub>Gly</jats:sub> but fail to release it, thus depleting the cellular tRNA <jats:sub>Gly</jats:sub> pool. This process caused stalling of translating ribosomes on glycine codons and activated the integrated stress response. Transgenic tRNA <jats:sub>Gly</jats:sub> overexpression prevented peripheral neuropathy and protein synthesis defects in mouse and fruit fly models. Thus, elevating tRNA <jats:sub>Gly</jats:sub> levels or targeting GCN2 may have therapeutic potential for this currently untreatable disease (see the Perspective by Mellado and Willis). —SMH </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:title>Making ribosomes in human cells</jats:title> <jats:p> The assembly of the human ribosome requires a vast number of assembly factors that first form a giant precursor of the ribosomal small subunit (SSU), the SSU processome. Singh <jats:italic>et al</jats:italic> . provide new insights into human ribosome assembly by using cryo–electron microscopy, x-ray crystallography, and functional studies to reveal the structures of the human SSU processome as it matures in the nucleolus. This study reveals the tightly controlled molecular choreography by which an ensemble of assembly factors controls early irreversible maturation steps that bring about the formation of the human SSU. —DJ </jats:p>