This Week in Science

Science  30 Jun 2006:
Vol. 312, Issue 5782, pp. 1844
  1. Take the Short Way Home

    CREDIT: WITTLINGER ET AL.

    Ants meander on the outward leg of a foraging trip, but take a direct route home. To do this, they must navigate by dead reckoning, which requires the ability to measure the distance traveled. How ants actually measure the distance has remained obscure. By the simple experiment of lengthening or shortening the ants' legs, Wittlinger et al. (p. 1965) now show that the ants measure distance by counting their steps.

  2. Precooling Climate

    A sudden and large cooling episode occurred in the North Atlantic region approximately 8200 years ago (the “8.2 ky event”) and punctuated the otherwise stable Holocene climate. Ellison et al. (p. 1929; see the news story by Kerr) present records of planktonic foraminifera from the subpolar North Atlantic Ocean which show that water in this region became colder and fresher more than 200 years before the 8.2 ky event. The 8.2 ky event was likely caused by meltwater discharge from the Laurentide Ice Sheet that began centuries before the major cooling episode and may have been related to changes in the strength of deep-ocean circulation.

  3. Moving Slowly but Surely

    CREDIT: HSU ET AL.

    Motion along faults is most commonly associated with earthquakes, but aseismic slip occurs as well. Hsu et al. (p. 1921) analyzed data from continuously recording global positioning satellite stations above and near the Sunda megathrust rupture region after the 28 March 2005 Nias-Simeulue earthquake off Sumatra. Aseismic afterslip is still occurring on the subduction megathrust near the location of the 2005 rupture, mostly in updip direction, at rates several times greater than the average interseismic rate; the energy released is equivalent to a moment magnitude 8.2 earthquake. Bands of aftershocks are also seen, and their number scales with postseismic displacements, which indicates that most of the aftershocks are caused by the afterslip and not by the main shock.

  4. Toward Plastics from Sugar

    Because commercial chemicals often have petroleum as their ultimate source, there is great interest in the use of renewable sources such as biomass as alternative feedstocks. Román-Leshkov et al. (p. 1933) present an efficient route to 5-hydroxymethylfurfural, a furan derivative with strong potential for use in polyester synthesis, via the acid-catalyzed dehydration of fructose. They used a biphasic system in which the reaction occurred in an aqueous solution, with polar aprotic additives such as dimethylsulfoxide enhancing selectivity. The product was continuously extracted into a low-boiling organic phase. The system achieves >80% selectivity for the desired product at 90% fructose conversion.

  5. A Companion for Ferrate

    The rare example of iron in the +6 oxidation state is the ferrate ion, FeO42−, and the extremely powerful oxidizing properties of this species has spurred a long search for additional hexavalent iron compounds. Berry et al. (p. 1937, published online 1 June) report that successive electrochemical oxidation and photolysis of an Fe(IV) azide complex yields an octahedrally coordinated nitrido Fe(VI) compound that is stable at 77 kelvin. Spectroscopic characterization and supporting density functional theory are consistent with a diamagnetic ground state and an iron-nitrogen triple bond. Upon warming, the compound behaves as a three-electron oxidant.

  6. A Small Director

    Enzymes often achieve selectivity by aligning substrates in specific orientations through hydrogen bonding. Das et al. (p. 1941; see the Perspective by Mas-Ballesté and Que) show that even a small molecular catalyst can induce such alignment effects. They prepare a dimanganese complex with a carefully placed carboxylic acid (COOH) group in the ligand. Hydrogen bonding between this group and a substrate's carboxylic substituent leads to oxidation of a specific C-H bond on the other side of the substrate; modeling studies suggest that this oxidized site is oriented proximal to the manganese centers. Control experiments confirm that selectivity is lost when the COOH group is removed from the catalyst, or when acetic acid is added to disrupt the docking interaction.

  7. Plant Productivity Benefits of High Carbon Dioxide Busted

    Although rising CO2 levels may reduce global crop yields through the effects of higher temperatures and decreased soil moisture, arguments have been made that direct fertilization effects will more than offset these losses. Long et al. (p. 1918; see the Perspective by Schimel) present a critical analysis of data on which the Intergovernmental Panel for Climate Change base their projections that elevated CO2 will have a fertilizing effect. The original estimates came from experiments conducted in the 1980s in greenhouses and sheltered enclosures. More sobering figures are derived from open-field studies in which increased CO2 levels enhanced crop yields ∼50% less than in enclosure studies.

  8. The Rise and Rise of Resistant Tuberculosis

    Tuberculosis is spreading in a piggyback fashion along with infection by human immunodeficiency virus, with nearly 9 million cases estimated in 2003. Patients often do not complete the long treatment regimes, and thus help Mycobacterium tuberculosis develop antibiotic resistance. Gagneux et al. (p. 1944) show that rifampin-resistance mutations, such as rpoB S531L, have low fitness cost and are selected in patients during treatment and that these strains are the most prevalent in clinical isolates and more likely to spread in human populations.

  9. Do As I Say, Not As I Do

    CREDIT: RHEE ET AL.

    The cycle of hair growth and replenishment depends on a steady reserve of stem cells in the hair follicle. As new cells are needed, progenitor cells give rise to differentiated cells. Rhee et al. (p. 1946) now survey the transcriptional profile of progenitor cells to identify a gene that helps these cells generate differentiated daughters when needed but refrain from differentiating themselves. The gene encodes a transcription factor, Lhx2, already known for its effects in brain development and hematopoiesis.

  10. Advancing Spring Migrations

    Migratory birds, especially short-distance migrants, have advanced their spring arrival at their breeding grounds in reponse to climate change. Jonzén et al. (p. 1959) show that the timing of migration in long-distance migrants has advanced at least to the same extent as in short-distance migrants. Many long-distance migrant species wintering south of the Sahara desert are arriving in southern Europe progressively earlier. In Northern Europe, earlier arrival is not a simple effect of increased migration speed through Europe in response to increased temperature en route. Although improved foraging conditions across the African continent cannot be ruled out as an explanation, a more parsimonious hypothesis is an evolutionary change in the timing of migration in Africa.

  11. Perfecting Proofreading

    Most eukaryotic RNAs contain noncoding sequences (introns) that must be removed by messenger RNA (mRNA) splicing. The content of the mRNA can also be modified by alternative splicing where some coding sequences (exons) are removed. The signals (splice sites) in the RNA that mark the boundaries between introns and exons are short and degenerate, which raises the possibility that they could be misidentified by the splicing machinery and gross errors introduced into mRNA. Mendes Soares et al. (p. 1961; see the Perspective by Kress and Guthrie) now show that the protein DEK, previously implicated in autoimmunity and cancer, functions as part of a proofreading device for recognition of consensus 3′-AG splice sites by U2 auxiliary factor (U2AF). Phosphorylation of DEK promotes its binding to the U2AF35 subunit of U2AF, and this interaction minimizes the incorrect recognition of nonconsensus 3′-CG splice sites.

  12. We Feel Your Pain

    There is a widespread belief that empathy is a special human feature, or perhaps an exclusive ability of primates possessing theory of mind. Langford et al. (p. 1967; see the news story by Miller) performed a series of experiments with mice and observed that the mere observation of pain behavior in another mouse produces alterations in the pain behavior of the observer. Strikingly, these effects do not require genetic relationships between the observer and observed, but simply familiarity. The findings cannot be easily explained by stress, imitation, or conditioning, and may represent a nonprimate form of empathy.

  13. Scattering in Magnets Revealed

    Many theoretical predictions of the fundamental excitations in magnetic systems have proven difficult to confirm because the requisite experimental technique lacks sufficient resolution. Using a neutron-scattering method that combines spin-echo and triple-axis spectrometry, Bayrakci et al. (p. 1926; see the Perspective by Mesot) report high-resolution, low-temperature measurements of spin wave lifetimes in the prototypical antiferromagnet MnF2 over its entire Brillouin zone. This high-resolution technique offers new prospects for deeper understanding of magnetic systems.

  14. From One Glutamine to Another

    Recent genomic and biochemical evidence supports the view that the latecomers to the canonical set of 20 amino acids were first introduced with a cobbled-together system for attaching them to their cognate transfer RNAs (tRNAs); only eukaryotes and some eubacteria developed the appropriate aminoacyl-tRNA synthetases. One of these late additions, glutamine, is the subject of structural and biochemical studies in bacteria and archaea by Nakamura et al. (p. 1954) and Oshikane et al. (p. 1950). They describe the coordinated arrangement of heteromeric enzyme activities [glutamine amidotransferase CAB (GatCAB) and GatDE] that catalyze the detachment of the terminal ammonia group of free glutamine, transport it down a 35 angstrom tunnel, and subsequently reattach it to a tRNA-bound glutamate that is preactivated by phosphorylation of the terminal carboxylate. Furthermore, the GatDE-tRNA complex allows for the snug fit of the nondiscriminating GluRS (the synthetase that puts glutamate onto the glutaminyl-tRNA in the first step), which is reminiscent of how class I and class II synthetases interact with tRNAs.

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