Catálogo de publicaciones - revistas

<jats:title>To Degrade or Not to Degrade</jats:title> <jats:p> Regulating the turnover of proteins within the cell is of fundamental importance to almost every physiological process. <jats:bold> Hwang <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="973" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1183147">973</jats:related-article> , published online 28 January; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5968" page="966" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1187274">Mogk and Bukau</jats:related-article> </jats:bold> ) now find that acetylated N-terminal methionine (Met) is a degradation signal. This degron is recognized by <jats:italic>Saccharomyces cerevisiae</jats:italic> Doa10, a transmembrane E3 ubiquitin ligase that resides in the endoplasmic reticulum and inner nuclear membrane. The removal of N-terminal Met by Met-aminopeptidases generates N-terminal residues that are often N-terminally acetylated. Doa10 selectively binds to the resulting N-degrons, which may represent the most prevalent class of cellular protein degradation signals. </jats:p>

<jats:title>Detecting Distant Planets</jats:title> <jats:p> More than 400 planets have been detected outside the solar system, most of which have masses similar to that of the gas giant planet, Jupiter. <jats:bold> Borucki <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="977" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1185402">977</jats:related-article> , published online 7 January) summarize the planetary findings derived from the first six weeks of observations with the Kepler mission whose objective is to search for and determine the frequency of Earth-like planets in the habitable zones of other stars. The results include the detection of five new exoplanets, which confirm the existence of planets with densities substantially lower than those predicted for gas giant planets. </jats:p>

<jats:title>2D Quantum Critical Transitions</jats:title> <jats:p> Quantum critical transitions occur at near-zero temperatures when the properties of quantum matter are tuned by an external parameter such as the magnetic field or pressure. Heavy fermion materials, which have effective charge carrier masses hundreds of times heavier than the bare electron mass, have emerged as a prototypical system for studying these transitions. Now, <jats:bold> Shishido <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="980" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1183376">980</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="5968" page="969" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1186253">Coleman</jats:related-article> </jats:bold> ) use a heavy fermion compound to experimentally realize a new type of quantum phase transition where the tuning parameter is the dimensionality of the system. They engineer a family of superlattices made up of a fixed number of layers of the conventional metal LaIn <jats:sub>3</jats:sub> and varying numbers of layers of the heavy fermion material CeIn <jats:sub>3</jats:sub> . As the number of layers of CeIn <jats:sub>3</jats:sub> is decreased, the system gradually changes character from three- to two-dimensional, with corresponding changes in its transport properties. </jats:p>

<jats:title>Silicate in the Primordial Soup</jats:title> <jats:p> Direct evidence for how prebiotic synthesis of complex organic molecules paved the way for the origin of life is extremely scarce. Thus, studies are mainly limited to controlled simulations of likely reactions in early Earth conditions. Similarly, chemical reactions in the laboratory may generate the products necessary for biosynthesis, but may nevertheless be geochemically irrelevant. <jats:bold> Lambert <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="984" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1182669">984</jats:related-article> ) show that silicate ions, present in Earth's surface waters at relatively high concentrations, catalyze the formation of four- and six-carbon sugars from simple sugars via the formose reaction. The resulting complexes stabilize the sugar molecules, allowing sugars to accumulate in greater abundance. Silicate stabilization also circumvents the need for the formose reaction to proceed at high temperatures, thus extending the range of possible environments in which life could have originated. </jats:p>

<jats:title>Acid Assistance</jats:title> <jats:p> Protons are quite versatile catalysts of organic reactions, but because they are achiral, they cannot induce stereoselectivity on their own. One productive way around this problem has been to use chiral conjugate bases and perform reactions in media where the bases remain tightly attracted to protonated substrates. <jats:bold> Xu <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="986" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1182826">986</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="5968" page="965" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1186764">Schreiner</jats:related-article> </jats:bold> ) thoroughly explored the mechanism of an alternative approach, in which an achiral acid was used in conjunction with a second, chiral molecule (a urea derivative) for catalysis. High selectivity was attained with this method in the coupling of aryl imines with olefins. Extensive kinetic and computational studies showed that the acid and its chiral partner acted cooperatively in binding the substrates, optimizing the tradeoff between speed and selectivity. </jats:p>

<jats:title>From Big Fish to Big Whales</jats:title> <jats:p> Whales are the largest animals today, and many feed on the abundant plankton, particularly diatoms, in the oceans. Whales arose and diversified in the Cenozoic, about 30 to 40 million years ago (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5968" page="968" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1186904">Cavin</jats:related-article> </jats:bold> ). <jats:bold>Marx and Uhen</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="993" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1185581">993</jats:related-article> ) show that their diversity parallels the diversity of diatoms and changes in ocean temperature. Whether there were large predators of plankton before whales has been enigmatic, because the fossil record during the Mesozoic (245 to 65 million years ago) is sparse. <jats:bold> Friedman <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="990" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184743">990</jats:related-article> ) now show that a group of large fish filled this role for nearly 100 million years in the Mesozoic. Although not as large as whales, these globally distributed fish were still several meters long. Their extinction at the Cretaceous-Paleogene boundary 65.5 million years ago may have cleared the seas for the evolution of whales. </jats:p>

<jats:title>From Big Fish to Big Whales</jats:title> <jats:p> Whales are the largest animals today, and many feed on the abundant plankton, particularly diatoms, in the oceans. Whales arose and diversified in the Cenozoic, about 30 to 40 million years ago (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5968" page="968" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1186904">Cavin</jats:related-article> </jats:bold> ). <jats:bold>Marx and Uhen</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="993" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1185581">993</jats:related-article> ) show that their diversity parallels the diversity of diatoms and changes in ocean temperature. Whether there were large predators of plankton before whales has been enigmatic, because the fossil record during the Mesozoic (245 to 65 million years ago) is sparse. <jats:bold> Friedman <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="990" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184743">990</jats:related-article> ) now show that a group of large fish filled this role for nearly 100 million years in the Mesozoic. Although not as large as whales, these globally distributed fish were still several meters long. Their extinction at the Cretaceous-Paleogene boundary 65.5 million years ago may have cleared the seas for the evolution of whales. </jats:p>

<jats:title>Histones and Alternative Splicing</jats:title> <jats:p> Alternative splicing—the inclusion of different combinations of gene exons within a messenger RNA transcript—occurs in the majority of human genes and is regulated by basal and tissue-specific splicing factors, by transcription kinetics, and by chromatin structure. <jats:bold> Luco <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="996" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184208">996</jats:related-article> , published online 4 February) analyzed the alternative splicing of the <jats:italic>human fibroblast growth factor receptor 2</jats:italic> gene in tissue culture cells and found that inclusion of exon IIIb or IIIc was modulated by the levels of histone H3 lysine 36 trimethylation (H3-K36me3) and H3-K4me3. Histone H3-K36me3 enrichment correlated with binding of the chromatin protein, MRG15. The MRG15 protein in turn recruited the polypyrimidine tract–binding protein (PTB) splicing factor, which acts to repress alternative exon inclusion, thus establishing a direct link between histone modifications and the splicing machinery. </jats:p>

<jats:title>Metabolic Regulation Through Acetylation</jats:title> <jats:p> Covalent modification of lysine residues in various proteins in the nucleus is a recognized mechanism for control of transcription. Now two papers suggest that acetylation may represent an important regulatory mechanism controlling the function of metabolic enzymes (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5968" page="964" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1187159">Norvell and McMahon</jats:related-article> </jats:bold> ). <jats:bold> Zhao <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="1000" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1179689">1000</jats:related-article> ) found that a large proportion of enzymes in various metabolic pathways were acetylated in human liver cells. Acetylation regulated various enzymes by distinct mechanisms, directly activating some, inhibiting one, and controlling the stability of another. Control of metabolism by acetylation appears to be evolutionarily conserved: <jats:bold> Wang <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="1004" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1179687">1004</jats:related-article> ) found that the ability of the bacterium <jats:italic>Salmonella entericum</jats:italic> to optimize growth on distinct carbon sources required differential acetylation of key metabolic enzymes, thus controlling flux through metabolic pathways. </jats:p>

<jats:title>Metabolic Regulation Through Acetylation</jats:title> <jats:p> Covalent modification of lysine residues in various proteins in the nucleus is a recognized mechanism for control of transcription. Now two papers suggest that acetylation may represent an important regulatory mechanism controlling the function of metabolic enzymes (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5968" page="964" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1187159">Norvell and McMahon</jats:related-article> </jats:bold> ). <jats:bold> Zhao <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="1000" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1179689">1000</jats:related-article> ) found that a large proportion of enzymes in various metabolic pathways were acetylated in human liver cells. Acetylation regulated various enzymes by distinct mechanisms, directly activating some, inhibiting one, and controlling the stability of another. Control of metabolism by acetylation appears to be evolutionarily conserved: <jats:bold> Wang <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="1004" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1179687">1004</jats:related-article> ) found that the ability of the bacterium <jats:italic>Salmonella entericum</jats:italic> to optimize growth on distinct carbon sources required differential acetylation of key metabolic enzymes, thus controlling flux through metabolic pathways. </jats:p>