Catálogo de publicaciones - revistas

<jats:title>CO on a Chip</jats:title> <jats:p> Microfluidics technology has facilitated remarkable miniaturization of chemical synthesis platforms; through electrically gated solution flow and mixing, molecular reactions can be carried out on chips several centimeters across. When it comes to more fundamental dynamics studies, though, which involve probing gas-phase molecules in specific quantum mechanical states, the experiments still tend to require much larger interaction areas. <jats:bold> Meek <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="1699" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175975">1699</jats:related-article> ) take a step toward miniaturization in this latter regime by demonstrating the isolation of a cold gas-phase beam of CO molecules just above a microelectrode-decorated chip. The technique relies on rapidly modulated electric fields that trap and then slow down the incoming molecules through dipole interactions. Once brought to a stop, the molecules can be held on the chip for a discrete period and then released to a detector. </jats:p>

<jats:title>Going Faster</jats:title> <jats:p> The concentrations of most tropospheric pollutants and trace gases are kept in check by their reactions with hydroxyl radicals (OH). OH is a short-lived, highly reactive species that is produced in the atmosphere by photochemical processes, and regenerated in the chain of chemical reactions that follows the oxidative destruction of those molecules. These regeneration mechanisms were thought to be fairly well understood, but now <jats:bold> Hofzumahaus <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="1702" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1164566">1702</jats:related-article> , published online 4 June) present evidence of a pathway not previously recognized. In a study of atmospheric composition in the Pearl River Delta, a highly polluted region of China, greatly elevated OH concentrations were observed without the correspondingly high levels of ozone expected from current models. Thus, OH concentrations may be augmented by a process that speeds the regeneration of OH without producing ozone. </jats:p>

<jats:title>Two's a Crowd</jats:title> <jats:p> The process by which males and females compete to maximize their individual fitness also affects the fitness of their offspring. Sexual selection largely results from polyandry (multiple mating by females), and several competing hypotheses attempt to explain the evolution of polyandry. <jats:bold> Bilde <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="1705" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171675">1705</jats:related-article> ) staged double mating experiments in seed beetles to distinguish between the theories underlying cryptic female choice and sexual antagonism. Contrary to expectation, males of high genetic quality, as measured on the basis of the number of offspring sired when singly mated to a female, consistently produced fewer offspring when females were doubly mated to males of both high and low genetic quality. Thus, postmating sexual selection can favor male genotypes with low fitness, and females risk genetic costs when mating with multiple males. </jats:p>

<jats:title>Integrating Organ Induction</jats:title> <jats:p> During animal development, multiple signaling pathways specify the induction of organ progenitors such as those in the pancreas and liver. <jats:bold>Wandzioch and Zaret</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1707" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1174497">1707</jats:related-article> ) investigated how three signaling pathways converge on the earliest genes specifying these organs. Within hours, multiple changes were observed in the inductive network with different signals operating in parallel. The findings may help to explain the incomplete programming seen in various stem cell differentiation protocols. </jats:p>

<jats:title>Of Life, Limb, and a Small RNA</jats:title> <jats:p> Gene expression in mammals is controlled not only by proteins but by small noncoding RNAs called microRNAs. The involvement of these RNAs provides powerful clues about the molecular origins of human diseases and how they might be treated. Ischemic diseases arise from an inadequate blood supply. <jats:bold> Bonauer <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="1710" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1174381">1710</jats:related-article> , published online 21 May) find that a specific microRNA that is expressed in the cells lining blood vessels (called miR-92a) functions to repress the growth of new blood vessels. MiR-92a probably acts through effects on expression of integrins, proteins involved in cell adhesion and migration. In mouse models in which an inadequate blood supply had caused damage either to heart or limb muscle, therapeutic inhibition of miR-92a led to an increase in blood vessel density in the damaged tissues and enhanced functional recovery. </jats:p>

<jats:title>Ras, STAT3, and Transformation</jats:title> <jats:p> The STAT (signal transducer and activator of transcription) proteins are activated in response to receptor stimulation and act in the nucleus to regulate gene expression. <jats:bold> Gough <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="1713" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171721">1713</jats:related-article> ) found that STAT3 functioned in transformation of cells by the oncogene Ras. However, this activity was maintained in mutants of STAT that fail to activate transcription. Instead, the active STAT3 appeared to be associated with mitochondria. Furthermore, modified STAT3 targeted to the mitochondria promoted transformation by Ras, and mitochondrial function was disrupted in Ras-transformed cells lacking STAT3. Such transformation-specific effects of STAT3 could be a useful target in developing anticancer therapies. </jats:p>

<jats:title>Synthetic Centromere</jats:title> <jats:p> Every eukaryotic chromosome must have a centromere where the cell division machinery latches onto each chromosome pair to ensure an even apportioning of the genetic material between daughter cells. The characteristic (but not conserved) repeat sequences associated with most centromeres are thought to be required to induce an RNA interference (RNAi) response and thereby promote the formation of heterochromatin, needed for centromere function. <jats:bold> Kagansky <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="1716" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172026">1716</jats:related-article> ) now show in fission yeast that these outer repeat sequences can be replaced in their entirety by very short sequences that recruit an enzyme, Clr4, which promotes the formation of heterochromatin in the absence of RNAi. Thus, flanking heterochromatin, regardless of its derivation, is all that is required for the formation of a functional centromere. </jats:p>

<jats:title>Transcriptional Regulation Gets More Complicated</jats:title> <jats:p> Sequence preferences of DNA binding proteins are a primary mechanism by which cells interpret the genome. A central goal in genome biology is to identify regulatory sequences in the genome; however, few proteins' DNA binding specificities have been characterized comprehensively. <jats:bold> Badis <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="1720" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1162327">1720</jats:related-article> , published online 14 May) studied 104 known and predicted transcription factors (TFs), spanning 22 structural classes, in the mouse genome. While traditional models of TF binding sites are based on a single collection of highly similar DNA sequences, binding profiles were represented better by multiple motifs. Roughly half of the TFs recognized distinct primary and secondary motifs that are different from each other. At least some of these interaction modes appeared to be attributable to biophysically distinct protein conformations, adding to the complexity of transcriptional regulation. </jats:p>

<jats:title>Green for Diatoms</jats:title> <jats:p> Diatoms account for 20% of global carbon fixation and, together with other chromalveolates (e.g., dinoflagellates and coccolithophorids), represent many thousands of eukaryote taxa in the world's oceans and on the tree of life. <jats:bold> Moustafa <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="1724" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172983">1724</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1651" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175765"> <jats:bold>Dagan and Martin</jats:bold> </jats:related-article> </jats:bold> ) have discovered that the genomes of diatoms are highly chimeric, with about 10% of their nuclear genes being of foreign algal origin. Of this set of 1272 algal genes, 253 were, as expected, from a distant red algal secondary endosymbiont, but more than 1000 of the genes were derived from green algae and predated the red algal relationship. These protist taxa are important not only for genetic and genomic investigations but also for their potential in biofuel and nanotechnology applications and in global primary productivity in relation to climate change. </jats:p>

<jats:title>Opening the Portico</jats:title> <jats:p> <jats:italic>Escherichia coli</jats:italic> diacylglycerol kinase (DAGK) represents a family of integral membrane phosphotransferases that function in prokaryotic-specific metabolic pathways. <jats:bold> Van Horn <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="1726" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171716">1726</jats:related-article> ) determined the structure of the 40-kilodalton functional homotrimer of <jats:italic>E. coli</jats:italic> DAGK by solution nuclear magnetic resonance spectroscopy. Each monomer comprises three transmembrane helices. The third transmembrane helix from each subunit is domain-swapped to pack against the first and second transmembrane helices from an adjacent subunit. These three helices frame a portico-like membrane-submerged cavity that contains residues critical for activity in close proximity to residues critical for folding. The structure provides insight into the determinants of lipid substrate specificity and phosphotransferase activity. </jats:p>