Catálogo de publicaciones - revistas

<jats:title>Keeping DNA Flexible</jats:title> <jats:p> The elastic behavior of DNA is important to biological processes that involve DNA bending and looping. However, there has been considerable debate over the flexibility of DNA at lengths below the persistence length (around 150 base pairs). A widely used approximation, the wormlike chain model, predicts stiff short DNA. <jats:bold>Vafabakhsh and Ha</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1097" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224139">1097</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6098" page="1045" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1227014">Nelson</jats:related-article> </jats:bold> ) directly monitored cyclization of single molecules of DNA, by using a fluorescence assay, and found significant looping, with the looping rate having only weak length dependence between 67 and 105 bp, which is inconsistent with the wormlike chain model. Instead, DNA binding proteins may stabilize transiently bent or looped DNA conformations. </jats:p>

<jats:title>Good Enough Can Be Good Enough</jats:title> <jats:p> To begin to understand why some enzymes are promiscuous and have many substrates, whereas others are highly specific, and why some have high activity, whereas others appear not to be optimized, <jats:bold> Nam <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="1101" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1216861">1101</jats:related-article> ) analyzed metabolic networks in bacteria. Specialist enzymes are essential for life, catalyze a high flux of enzymatic activity, and are more highly regulated. However, not all enzymes appear to be on a track of gradual improvement of specificity and efficiency. Generalist enzymes seem to well serve their own purposes, and their optimization may not justify the evolutionary cost. </jats:p>

<jats:title>Ocean Methane</jats:title> <jats:p> Is methylphosphonate a natural product? If it is, then its catabolism by microrganisms seeking phosphorus might explain the ubiquity of methane in the oceans. Anaerobic Archaea, so far, are the only significant source of methane known. Thus, <jats:bold> Metcalf <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="1104" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1219875">1104</jats:related-article> ) looked for evidence of methylphosphonate biochemistry in the widespread archaeon <jats:italic>Nitrosopumilus maritimus.</jats:italic> The organism can synthesize C-P bonds using phosphoenolpyruvate mutase. By using its gene, <jats:italic>ppm</jats:italic> , as a marker, a possible phosphonate biosynthesis gene cluster was identified, and adjacent to this a gene for a cupin was found. Together with Fe(II) and O <jats:sub>2</jats:sub> the cupin catalyzed the production of methylphosphonate and formate. Homologs of the cupin gene are found in a wide range of common marine microbes, including <jats:italic>Pelagibacter ubique</jats:italic> and <jats:italic>Prochlorococcus.</jats:italic> </jats:p>

<jats:title>From Farm to Clinic?</jats:title> <jats:p> Soil organisms have long been assumed to be an important source of antibiotic resistance genes, in part because of antibiotic-treated livestock and in part because of the natural ecology of antibiotic production in the soil. <jats:bold> Forsberg <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="1107" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1220761">1107</jats:related-article> ) developed a metagenomic protocol to assemble short-read sequence data after antibiotic selection experiments, using 12 different drugs in all antibiotic classes, and compared antibiotic resistance gene sequences between soil bacteria and clinically occurring pathogens. Sixteen sequences, representing seven gene products, were discovered in farmland soil bacteria within long stretches of perfect nucleotide identity with pathogenic proteobacteria. </jats:p>

<jats:title>A Double Escapee</jats:title> <jats:p> Toll-like receptors (TLRs)—TLR2 and TLR7—are thought to contribute to the sensing of Gram-positive bacteria like <jats:italic>Staphylococcus aureus</jats:italic> and <jats:italic>Streptococcus pneumoniae</jats:italic> by the immune system. Mice deficient in these receptors, however, are still sensitive to infection with these bacteria. <jats:bold> Oldenburg <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="1111" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1220363">1111</jats:related-article> , published online 19 July) demonstrate that TLR13 also plays a role in detecting Gram-positive bacteria. TLR13 recognized a conserved region in the peptidyl transferase loop of bacterial 23S ribosomal RNA. Intriguingly, this same sequence is modified by specific methyltransferases that confer resistance to erythromycin. Indeed, erythromycin-resistant bacteria were no longer detectible by TLR13. </jats:p>

<jats:title>Skin Specifics</jats:title> <jats:p> Much of the recent attention paid to the trillions of bacteria that colonize our bodies has been given to the bacteria that reside in the gut. <jats:bold> Naik <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="1115" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1225152">1115</jats:related-article> , published online 26 July) report that colonization of the skin with commensal bacteria is important for tuning effector T cell responses in the skin and for protective immunity against cutaneous infection with the parasite <jats:italic>Leishmania major</jats:italic> in mice. In contrast, selective depletion of the gut microbiota, which plays an important role in modulating immune responses in the gut, had no impact on T cell responses in the skin. </jats:p>

<jats:p>Targeted proteomics is homing in on promising biomarkers to help screen for cancer and guide patient treatment, but much work still needs to be done to validate these biomarkers and develop technology capable of bringing them to the clinic.</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:p>China has made great strides in a wide range of research areas, from mathematics to astronomy to genomics. As the largest scientific organization in China, the Chinese Academy of Science (CAS) is a major driving force behind these advances. Through support and guidance from CAS, China is focused on building "big science" infrastructure, as well as on developing a talent pool of top notch scientists for the country. This talent pool is being built through programs to retain and cultivate the best Chinese scientists (while encouraging them to travel globally for training and to develop collaborations), as well as numerous incentive programs for international scientists to visit and work in China.</jats:p> <jats:p>CAS supports cutting-edge research in many of the fields currently seen worldwide as areas of intense interest and investigation. These include stem cell research and regenerative medicine, global climate change (and its effect on world populations and economies), and the development of new green science technologies that not only reduce carbon emissions, but also provide new, cleaner, and more efficient sources of energy. The Academy also provides strong support for the transfer of new, innovative technologies from the laboratory to industry, a process through which discoveries made locally can benefit people across the globe.</jats:p> <jats:p>As China moves into a new era of economic prosperity and scientific success, the role of CAS will undoubtedly grow, both domestically and globally. By maintaining its focus on innovation, nurturing exceptional talent, and building additional S&amp;T capacity, CAS will surely meet the challenges of the coming years from a position of stability and strength.</jats:p>

<jats:p>The show includes a reservoir of antibiotic resistance, forests that control the rain, the latest in Denisovan DNA, and more.</jats:p>