Catálogo de publicaciones - revistas

<jats:title>Respiration Refined</jats:title> <jats:p> Cells derive energy from redox reactions mediated by mitochondrial enzymes that form the electron transport chain. The enzymes can form large complexes, known as supercomplexes, whose function has been controversial. <jats:bold> Lapuente-Brun <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6140" page="1567" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1230381">1567</jats:related-article> ) discovered that a mouse protein, supercomplex assembly factor I (SCAFI), specifically modulates assembly of respiratory complexes into supercomplexes. Formation of the supercomplexes appears to cause electrons to be processed differently, depending on the substrate from which they are derived. </jats:p>

<jats:title>Threading Through</jats:title> <jats:p> Protein antibiotics (bacteriocins) are frequently deployed by Gram-negative bacteria to combat competitors, a trait common in pathogens such as <jats:italic>Escherichia coli, Yersinia pestis, Pseudomonas aeruginosa, Xanthomonas campestris</jats:italic> , and <jats:italic>Klebsiella pneumonia</jats:italic> . As a result, bacteriocins are being developed as species-specific antibacterials. Bacteriocins must establish a translocon at the bacterial outer membrane in order to translocate into cells. Working in <jats:italic>E. coli</jats:italic> , <jats:bold> Housden <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6140" page="1570" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1237864">1570</jats:related-article> ) describe how the deoxyribonuclease, colicin E9, crosses the bacterial cell membrane by threading through a porin. </jats:p>

<jats:title>Desert Soil Shuffle</jats:title> <jats:p> Soil microorganisms make up a substantial fraction of global biomass, turning over carbon and other key nutrients on a massive scale. Although the soil protects them somewhat from daily temperature fluxes, the distribution of these communities will likely respond to gradual climate change. <jats:bold> Garcia-Pichel <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6140" page="1574" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1236404">1574</jats:related-article> , see the cover; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6140" page="1533" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1240318">Belnap</jats:related-article> </jats:bold> ) surveyed bacterial diversity across a range of North American desert soils, or biocrusts—ecosystems in which photosynthetic bacteria determine soil fertility and control physical soil properties such as erodability and water retention. Most of the sites were dominated by one of two cyanobacterial species, but their relative proportions were controlled largely by factors related to temperature. Laboratory enrichment cultures of the two species at different temperatures also showed temperature as a primary determining factor of bacterial diversity. It is unknown if temperature will affect the distribution of other soil microorganisms, but the marked shifts of these two keystone bacterial species suggest further change is in store for these delicate ecosystems. </jats:p>

<jats:title>Stopping Transcription</jats:title> <jats:p> It is as important to terminate any biological process as it is to start it. Transcription, copying information encoded in genes into RNA, requires accurate and timely termination. <jats:bold> Nielsen <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6140" page="1577" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1237934">1577</jats:related-article> ) present a mechanism for transcription termination by RNA polymerase III, the enzyme that synthesizes the majority of RNA molecules in eukaryotes. In this scenario, the folding of the RNA as it is transcribed by polymerase into a highly structured transcript causes termination at the end of its synthesis. This mechanism may serve as a control of proper folding of structural or catalytic RNAs synthesized by RNA polymerase III. Comparison with other organisms suggests that this mechanism emerged before divergence of bacteria and eukaryotes. </jats:p>

<jats:title>Keeping Transcription Going</jats:title> <jats:p> In cells, the DNA double-stranded helix (dsDNA) is mostly supercoiled—either under- or overwound. RNA polymerase (RNAP) must transcribe though this supercoiled DNA. Furthermore, the act of transcription, which involves opening the double helix and threading the separated strands through the enzyme, generates supercoiling ahead and behind the polymerase. <jats:bold> Ma <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6140" page="1580" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1235441">1580</jats:related-article> ) used single-molecule methods to measure the upstream and downstream torque forces of <jats:italic>Escherichia coli</jats:italic> RNAP. The upstream torque was sufficient to disrupt dsDNA structure, and the stalled RNAP could also backtrack along the DNA. Release of the torsional stress allowed RNAP to resume transcription in vitro. </jats:p>

<jats:title>Unreactive Death</jats:title> <jats:p> A controversial proposal that all bactericidal antibiotics kill by reactive oxygen species (ROS) and not by their primary cell target has recently attracted high-profile refutations. The ROS-death pathway implicated overstimulation of the electron transport in respiratory chains; a malfunction that leads to ROS releasing Fe from Fe-S clusters and causing cell death via Fenton chemistry. <jats:bold> Ezraty <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6140" page="1583" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1238328">1583</jats:related-article> ) show that electron transport chains and Fe-S clusters are key to killing by aminoglycoside antibiotics but not for the reasons envisioned in the ROS theory. Fe-S clusters are essential for killing because they mature the respiratory chains that produce the necessary proton motive force for the energized uptake of aminoglycosides. Consequently, iron chelators protect against aminoglycosides, not because they scavenge the iron from Fenton chemistry, but because they block aminoglycoside uptake. </jats:p>

<jats:title>B Cell Tug of War</jats:title> <jats:p> High-affinity, protective antibodies made by B cells are critical for providing long-term protection against reinfection. In order to produce antibodies, B cells must first bind to and extract antigens from the surface of antigen-presenting cells. Using an in vitro system that allows B cells to bind to antigenladen, flexible membranes, <jats:bold> Natkanski <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6140" page="1587" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1237572">1587</jats:related-article> , published online 16 May) show that antigen extraction relies on myosin IIA–mediated contractile forces that pull upon the antigen-presenting membrane. These forces break the antigen-receptor bonds if affinity is low, thus ensuring that B cells only extract, internalize, and presumably respond to, high-affinity antigens. </jats:p>

<jats:title>A Direct Line in the Brain</jats:title> <jats:p> For decades, neuroscientists have assumed that there is a “canonical microcircuit” in the neo cortex, in which information is transformed as excitation spreads serially along connections from thalamus, to cortical layer 4, then to layers 2/3, to layers 5/6, and finally to other brain regions. Each cortical layer is thought to transform sensory signals to extract behaviorally relevant information. Now, <jats:bold>Constantinople and Bruno</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6140" page="1591" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1236425">1591</jats:related-article> ) challenge this dogma. In vivo whole-cell recordings revealed that sensory stimuli activate neurons in deep cortical layers simultaneously to those in layer 4 and that a large number of thalamic neurons converge onto deep pyramidal neurons, possibly allowing sensory information to completely bypass upper layers. Temporary blockade of layer 4 revealed that synaptic input to deep cortical layers derived entirely from the thalamus and not at all from upper cortical layers. This thalamically derived synaptic input reliably drove pyramidal neurons in layer 5 to discharge action potentials in the living animal. These deep layer neurons project to numerous higher-order brain regions and could directly mediate behavior. </jats:p>

<jats:p>Listen to stories on the fate of topsoil microbes under climate change, observations from Voyager 1, attacking cancer with the immune system, and more.</jats:p>

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