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The evolutionary origin of the human malaria parasitePlasmodium falciparum has been traced to a fellow primate, probably the result of a single host transfer event. Genetic analysis of thousands of fecal samples from African apes shows that the parasites from western gorillas rather than those in chimpanzees or bonobos are most closely related to the human form. The cover shows a western lowland gorilla. Picture credit: George Logan/Corbis
An ambitious project to track greenhouse gases from a perch high above the Amazon forest will provide crucial data — but only if scientists can get it built.
The continent's patent system is Byzantine, but current proposals for a new EU-wide patent could make matters worse, warns Bruno van Pottelsberghe de la Potterie.
Plasmodium falciparum is the agent of the deadliest form of human malaria. A survey of Plasmodium diversity in African apes reveals that western gorillas are the reservoir species for this parasite. See Article p. 420
A fresh analysis of data from gravitational microlensing surveys for planets orbiting stars other than the Sun finds that gas-giant planets similar to Jupiter are more common than previously thought.
Enhancer sequences increase gene transcription with the help of a co-activator complex, the Mediator. Another protein complex — cohesin — seems to work with Mediator to bring together enhancers and promoters. See Article p. 430
Nanoparticles that generate light through a mechanism known as second harmonic generation have been used to image live tissue. The particles overcome many problems associated with fluorescent probes for bioimaging.
A fine marriage between two approaches to X-ray microscopy — computed tomography and ptychographic imaging — delivers high-resolution, three-dimensional images of samples without the need for lenses. See Letter p. 436
How does a Salmonella pathogen outcompete beneficial intestinal microorganisms? It triggers an immune response that generates a compound from intestinal gas that it can utilize as an energy source. See Article p. 426
Theory suggests that the risk of critical transitions in complex systems can be revealed by generic indicators. A lab study of extinction in plankton populations provides experimental support for that principle. See Letter p. 456
Do excited molecules relaxing to their ground state pass through a 'seam' connecting the potential energy profiles of the states? Experimental data suggest the answer to this long-standing question is 'yes'. See Letter p. 440
The evolutionary origin of the human malaria parasite Plasmodium falciparum has been much debated. Genetic analysis of a large number of faecal samples from wild-living African apes now shows that Plasmodium parasites from Western gorillas are most closely related to the human parasite. The data suggest that human P. falciparum evolved from a gorilla parasite after a single host transfer event.
Salmonella enterica serotype Typhimurium causes acute gut inflammation, which promotes the growth of the pathogen through unknown mechanisms. It is now shown that the reactive oxygen species generated during inflammation react with host-derived sulphur compounds to produce tetrathionate, which the pathogen uses as a terminal electron acceptor to support its growth. The ability to use tetrathionate provides the pathogen with a competitive advantage over bacteria that lack this property.
Gene activation may involve the formation of a DNA loop that connects enhancer-bound transcription factors with the transcription apparatus at the core promoter. But this process is not well understood. Here, two proteins, mediator and cohesin, are shown to connect the enhancers and core promoters of active genes in embryonic stem cells. These proteins seem to generate cell-type-specific DNA loops linked to the gene expression program of each cell.
Ptychographic X-ray imaging is a powerful technique for extracting detailed phase (and hence structural) information from weakly absorbing objects. Here it is shown how this technique can be combined with methods for tomographic reconstruction to generate full three-dimensional maps of the object under investigation. The approach has sensitivity to density variations of less than one per cent, and can resolve structures on the 100 nm length scale.
Chemical reactions are usually described in terms of the movement of nuclei between the potential energy surfaces of ground and excited electronic states. Crossings known as conical intersections permit efficient transitions between the surfaces. It is shown here that ultrafast optical spectroscopy, with sub-20-fs time resolution and spectral coverage from the visible to the near-infrared, can map the isomerization of rhodopsin with sufficient resolution to shown that a conical intersection is important in this crucial event in vision.
Global-mean surface temperatures have risen, fallen and risen again during the twentieth century, with some differences between the Northern and Southern hemispheres. The cooling is usually thought to be due to a peak in sulphate aerosol production or to changes in the climate of the world's oceans that arise over decades. Here it is shown that an abrupt change in sea surface temperatures accounts for much of the Northern Hemisphere cooling. The event was too rapid to have been caused by aerosols or multidecadal variability.
What defines the boundary between the Earth's lithosphere and asthenosphere? Here it is shown experimentally that the instability of the hydrous mineral pargasite at depths greater than about 90 km causes a sharp drop in the water-storage capacity of a fertile upper-mantle mineralogy, and accordingly a sharp drop in its solidus temperate. This effect might define the lithosphere–asthenosphere boundary.
Earthquake instability has long been attributed to fault weakening during accelerated slip, but what are the mechanisms that control this weakening? Here laboratory evidence is presented for the dynamic weakening of faults that are sheared at velocities approaching earthquake slip rates. The experimental faults, made from solid granite blocks, quickly wore to form a fine-grain rock powder, known as gouge, which reduced the faults' strength. It is concluded that only newly formed gouge can weaken the experimental faults.
Populations that become extinct because of environmental degradation pass a tipping point, after which extinction is inevitable. But theory predicts that the population's dynamics indicate what is coming beforehand, through the phenomenon of critical slowing down. It has now been shown that critical slowing down can be used to anticipate extinction in experimental populations of Daphnia magna.
Here, a combination of genetic studies of gene expression, cross-species network analysis and genome-wide association studies has been used to identify gene networks and the loci underlying their regulation in rats. The results show that an inflammatory network driven by interferon regulatory factor 7 contributes to susceptibility to type 1 diabetes, and implicate the innate viral-response pathway and macrophages in the aetiology of this disease.
B cells are activated by many different antigens to produce appropriate antibodies. B cells express up to 120,000 B-cell antigen receptor (BCR) complexes on their surface, but how do these complexes remain silent on resting B cells, and how are they activated? It is found here that the BCR on resting cells forms oligomers, and that these may be an autoinhibited form of the receptor. Disruption of the oligomer shifts B cells towards activation.
The translation of messenger RNA that lacks stop codons results in the production of aberrant proteins, which may have harmful effects on the cell. It is unclear how eukaryotic cells eliminate these 'non-stop' proteins. Here it is shown that, in Saccharomyces cerevisiae, an E3 ubiquitin ligase called Ltn1 acts in the quality-control pathway. It associates with ribosomes and marks non-stop proteins with ubiquitin, which targets the proteins for degradation.
Two classes of enzyme — cyclin-dependent kinases (CDK) and Dbf4-dependent kinase (DDK) — facilitate the initiation of DNA replication in eukaryotes. It is now shown that, when DNA damage is sensed, another kinase, Rad53, halts the firing of late replication origins by inhibiting both the CDK and the DDK pathways. Rad53 acts on DDK directly by inhibiting Dbf4, whereas the CDK pathway is blocked by Rad53-mediated phosphorylation of the downstream CDK substrate Sld3.
Two classes of enzyme — cyclin-dependent kinases (CDK) and Dbf4-dependent kinase (DDK) — facilitate the initiation of DNA replication in eukaryotes. It is now shown that, when DNA damage is sensed, another kinase, Rad53, halts the firing of late replication origins by inhibiting both the CDK and the DDK pathways. Rad53 acts on DDK directly by inhibiting Dbf4, whereas the CDK pathway is blocked by Rad53-mediated phosphorylation of the downstream CDK substrate Sld3.
Gram-negative bacteria, such as Escherichia coli, use tripartite efflux complexes in the resistance-nodulation-cell division family to expel toxic compounds from the cell. The CusCBA system is responsible for removing biocidal Cu(I) and Ag(I) ions. Here, the X-ray crystal structure is reported of CusA in the absence and presence of bound Cu(I) or Ag(I). The structures reveal that the metal-binding sites are located within the cleft region of the periplasmic domain. A potential pathway for ion export is proposed.