Catálogo de publicaciones - revistas

<jats:p>Parental genetic conflict may have exploited changes in the coding of a protein loop in a growth factor receptor.</jats:p>

<jats:title>Powering LPS Export</jats:title> <jats:p> The surface of Gram-negative bacteria such as <jats:italic>Escherichia coli</jats:italic> is covered in lipopolysaccharide (LPS), which must be synthesized within the cytoplasm and then exported across the periplasm to the outer leaflet of the outer membrane. <jats:bold> Okuda <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="1214" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1228984">1214</jats:related-article> , published online 8 November) describe the detection of LPS molecules bound to specific components of the <jats:italic>E. coli</jats:italic> lipopolysaccharide exporter during transport in vivo. In vitro reconstitution of LPS transport revealed the energetic requirements for the first two steps of transport, release from the membrane and transit along the periplasmic bridge of the exporter that connects the inner and outer membrane components. The findings suggest that adenosine triphosphate hydrolysis by a cytoplasmic component of the machine provides energy to push a continuous stream of LPS against its concentration gradient to the cell surface. </jats:p>

<jats:title>DNA Repair in Vitro</jats:title> <jats:p> Accurate replication of the genome is critical to an organism's continued survival. Damaged DNA not repaired before the commencement of replication can cause the DNA replication fork to stall or collapse, which can result in mutation or recombination, with potentially serious consequences for cell and organism. Fork regression involving a so-called “chicken foot” structure (Holliday junction) is thought to provide one mechanism for dealing with unrepaired DNA damage during replication. <jats:bold> Manosas <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="1217" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1225437">1217</jats:related-article> ) analyzed the action of the T4 bacteriophage replisome and helicase UvsW on a stalled-fork mimic in vitro, using a magnetic trap. UvsW was able to switch migration directions, which was essential for remodeling the stalled fork. Together, UvsW and T4 holoenzyme were able to drive template switching and lesion bypass in vitro. </jats:p>

<jats:p> Chronic infections strain the regenerative capacity of antiviral T lymphocyte populations, leading to failure in long-term immunity. The cellular and molecular events controlling this regenerative capacity, however, are unknown. We found that two distinct states of virus-specific CD8 <jats:sup>+</jats:sup> T cells exist in chronically infected mice and humans. Differential expression of the T-box transcription factors T-bet and Eomesodermin (Eomes) facilitated the cooperative maintenance of the pool of antiviral CD8 <jats:sup>+</jats:sup> T cells during chronic viral infection. T-bet <jats:sup>hi</jats:sup> cells displayed low intrinsic turnover but proliferated in response to persisting antigen, giving rise to Eomes <jats:sup>hi</jats:sup> terminal progeny. Genetic elimination of either subset resulted in failure to control chronic infection, which suggests that an imbalance in differentiation and renewal could underlie the collapse of immunity in humans with chronic infections. </jats:p>

<jats:title>Joy or Pain?</jats:title> <jats:p> Face recognition and processing are so completely central to human social interactions that these functions are supported by specialized regions in the brain. One of the fundamental aspects being processed is emotion, particularly whether the emotion being expressed is positive or negative. Nevertheless, neuroimaging studies have documented that perceiving opposite emotions often activates the same or overlapping regions. <jats:bold> Aviezer <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="1225" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1224313">1225</jats:related-article> ) report that the recognition of positive versus negative emotions actually relies on information communicated by the body—the extent to which perceivers identified joy versus grief in composite figures was driven by whether the body came from a joyous (versus grievous) image rather than the face. </jats:p>

<jats:title>Discerning a Difference</jats:title> <jats:p> Neighboring cells communicate via the Notch signaling pathway to make numerous decisions. Notch receptors are known to distinguish between two distinct ligand families, Delta and Serrate/Jagged, in different contexts. Posttranslational sugar modifications have been shown to play a role in this process, but it is not clear if other features of Notch are involved. Using a forward genetic approach in fruit flies, <jats:bold> Yamamoto <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="1229" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1228745">1229</jats:related-article> ) identified an evolutionarily conserved amino acid in the extracellular domain of Notch necessary for Serrate/Jagged signaling but dispensable for Delta signaling. </jats:p>

<jats:p>The show includes cracking crocodile scales, improving Myanmar's universities, the latest from MESSENGER, and more.</jats:p>

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