Catálogo de publicaciones - revistas

<jats:title>African Origins</jats:title> <jats:p> Humans originated in Africa and then spread across the globe. The high genetic diversity found in sub-Saharan Africa is consistent with this view, but the relationships among and within African populations have been less well explored. <jats:bold> Schlebusch <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="374" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1227721">374</jats:related-article> , published online 20 September) genotyped 220 individuals from 11 populations representing groups from Southern Africa to determine their relationships and history. The data suggest that modern-day human populations arose from a complex blend of mixing between groups and genetic stratification. </jats:p>

<jats:title>Transcription Around the Clock</jats:title> <jats:p> The biological clock that controls daily rhythms in mammalian physiology and behavior is thought to be regulated in large part by transcriptional events (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6105" page="338" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1230008"> <jats:bold>Doherty and Kay</jats:bold> </jats:related-article> ). <jats:bold> Koike <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="349" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226339">349</jats:related-article> ; published online 30 August) produced a comprehensive analysis of these transcriptional events across the entire mouse liver genome over a 24-hour period. Only ∼22% of cycling messenger RNA transcripts were driven by de novo transcription, suggesting that posttranscriptional events also play an important regulatory role in the mammalian clock. Biological timing in organisms can also respond to rhythmic cues from the environment. <jats:bold> Morf <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="379" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1217726">379</jats:related-article> , published online 23 August) explored how one such cue, cycles in ambient temperature, influence circadian timing in mammalian cells. Cold-inducible RNA–binding protein (CIRP) accumulates when body temperature is low. A systematic search for binding partners of CIRP identified RNA encoding core components of the circadian clock. Loss of CIRP decreased the amplitude of circadian gene expression and cells lacking CIRP adapted more quickly to temperature cycles. </jats:p>

<jats:title>Duplicate Gene, New Tricks</jats:title> <jats:p> The fact that functionally new genes appear is clear, but the evolutionary process that allows for a new gain of function is not well understood. <jats:bold> Näsvall <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="384" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226521">384</jats:related-article> ) present the innovation-amplification-divergence model which suggests that after gene duplication, ancestral function is maintained but that the duplicate copies can gain new function that is selected for through the accumulation of mutations or changes in expression. Experimental selection on <jats:italic>Salmonella enterica</jats:italic> allowed an ancestral gene to evolve new enzymatic function in fewer than 3000 generations. </jats:p>

<jats:title>Made and Modified</jats:title> <jats:p> The polytheonamides are 48-residue toxins derived from marine sponges that include 18 <jats:sc>D</jats:sc> -amino acids, as well as many other unusual amino acid modifications. Given the complexity, one might guess that these peptides are the product of nonribosomal, peptide synthetase (NRPS). However, <jats:bold> Freeman <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="387" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226121">387</jats:related-article> , published online 13 September now show that polytheonamides are produced by a bacterial symbiont using a ribosomal pathway. Six candidate enzymes for the 48 posttranslational modifications were identified and three were functionally validated. Such ribosomal systems could be useful in bioengineering. </jats:p>

<jats:title>Cleave and Leave</jats:title> <jats:p> Plants produce ethylene gas, which acts as a hormone and is essential for the ripening of fruit, the resistance of plants to pathogens, the adaptation of plants to stress conditions, and stem cell maintenance. Although many components of the ethylene gas signaling pathway have been well studied, little is known about how the ethylene receptors located in the endoplasmic reticulum (ER) membrane can transmit the signal to the nucleus. Studying <jats:italic>Arabidopsis</jats:italic> , <jats:bold> Qiao <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="390" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1225974">390</jats:related-article> , published online 30 August) found that perception of ethylene gas in the ER promotes signal transduction via cleavage and rapid ER-nucleus translocation of the cytosolic portion of the transmembrane ETHYLENE INSENSITIVE2 protein, which activates ethylene-dependent gene expression and other ethylene response phenotypes in plants. </jats:p>

<jats:title>A Fine Balance</jats:title> <jats:p> Intellectual and neurological disabilities can arise from diverse developmental aberrations. <jats:bold> Novarino <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="394" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1224631">394</jats:related-article> , published online 6 September; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6105" page="342" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1229178">Beaudet</jats:related-article> </jats:bold> ) have now determined the genetic basis for one such disorder for a small group of patients. Exome sequencing led to identification of mutations in a kinase <jats:italic>BCKDK</jats:italic> ( <jats:italic>Branched Chain Ketoacid Dehydrogenase Kinase</jats:italic> ) that regulates metabolism of branched-chain amino acids such as valine, leucine, and isoleucine. Mice with homozygous mutations in the <jats:italic>BCKDK</jats:italic> gene showed developmental and neurological abnormalities resembling those in certain mouse autism models. Analysis of transport mechanisms responsible for carrying amino acids across the blood-brain barrier revealed competition between the branched-chain amino acids and large neutral amino acids. Nutritional supplementation with extra branched-chain amino acids in the diet of mice carrying homozygous mutations in the <jats:italic>BCKDK</jats:italic> gene normalized their phenotype. </jats:p>

<jats:title>Making a Riboswitch</jats:title> <jats:p> During RNA synthesis by RNA polymerase (RNAP), nascent RNA will start to fold. This cotranscriptional folding can affect the final conformation and the function of the full-length RNA. Using single-molecule spectroscopy and optical tweezers, <jats:bold>Frieda and Block</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="397" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1225722">397</jats:related-article> ) followed the cotranscriptional folding of the <jats:italic>pbuE</jats:italic> riboswitch from <jats:italic>Bacillus subtilis</jats:italic> directly in real time, observing the formation of the adenine-binding aptamer structure or the alternative transcription terminator hairpin structure. The structures formed within seconds of their sequences clearing the RNAP footprint, confirming that the <jats:italic>pbuE</jats:italic> riboswitch is kinetically controlled. </jats:p>

<jats:p>The show includes twisted light, ejecting the Moon, male contraception, 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>