This Week in Science

Science  03 Mar 2000:
Vol. 287, Issue 5458, pp. 1553
  1. Old Stone Tools in China

    A variety of large tools, including hand axes and cleavers, referred to as Acheulean technology, have been found in Africa and Europe in the early Pleistocene (about 500,000 to 1,000,000 years ago). It was not clear whether Acheulean technology (or comparable tools) extended far to the east. Yamei et al. (p. 1622; see the cover and the news story by Gibbons) now describe an assemblage of Acheulean-like tools from the Bose Basin, South China. The tools are dated to 800,000 years ago (by dating of tektites associated with the tool deposits) and imply that comparable technologies arose or were present in the east and west by this time.

  2. Mars, North and South

    Martian surface spectra gathered by the thermal emission spectrometer onboard the Mars Global Surveyor have been used by Bandfield et al. (p. 1626; see the Perspective by Mittlefehldt) to evaluate the composition of the crust in 25 locations of relatively dark terrain. The older terrains in the southern hemisphere appear to be basaltic and resemble terrestrial basalts formed by primary melting at mid-oceanic ridges. The younger terrains in the northern hemisphere are more andesitic and resemble terrestrial volcanic rocks formed by mixed melting (basalt plus a more silica-rich continental crustal component) at subduction zones. The basaltic martian crust provides a better estimate of the composition of the mantle, whereas the andesitic rocks indicate that additional tectonic processes must have occurred during the planet's history to produce these more differentiated volcanic deposits.

  3. Ancient Oxygen

    The oxygen content of air (∼21%) is maintained by a complicated array of physical, chemical, geological, and biological processes. Berner et al. (p. 1630) examined the response of atmospheric oxygen levels to the dramatic changes in the Earth's tectonics, flora, and climate during the past 600 million years. Their reexamination of the existing carbon- and sulfur-isotopic geological records was based in part on experiments they performed which show that terrestrial plants fractionate carbon by different amounts depending on the oxygen content of the atmosphere in which they grow. They then constructed a history of atmospheric concentrations that stays within existing biological and physical constraints. For most of this period, atmospheric oxygen levels were roughly what they are today or even lower, but during the Carboniferous period 300 million years ago, when many insects were gigantic and thick forests covered much of the globe, the concentration of atmospheric oxygen was nearly 35%.

  4. Watching a Slow Burn

    Cytochrome P450 enzymes participate in the biosynthesis of steroids and lipids and also in the detoxification of foreign molecules. They can oxidize saturated hydrocarbons, a reaction that normally requires combustion conditions, by splitting molecular oxygen and using one of the oxygen atoms to form a hydroxyl group on the substrate molecule. Schlichting et al. (p. 1615) have cleverly adapted an x-ray crystallography approach to obtain evidence for the structures of several intermediates in the reaction, most notably the long-sought ferryl-oxygen species. After obtaining the diffraction pattern of the crystallized enzyme-substrate complex with short-wavelength x-rays, they used long-wavelength x-rays to cleave a water molecule. This step released the essential second electron that splits the bound dioxygen and to yield the proposed ferryl(IV)-oxygen species. This intermediate then inserts the oxygen atom into a carbon-hydrogen bond of the substrate in the hydroxylation step.

  5. Greener Route for Alcohol Oxidation

    Alcohols are among the organic chemist's most versatile starting materials, as their oxidation can yield aldehydes, ketones, and acids. Unfortunately, the inorganic oxidants used in these conversions are not catalysts (and thus generate heavy-metal wastes) and are often run in chlorinated solvents. Ten Brink et al. (p. 1636; see the news story by Service) report that a water-soluble palladium complex can use pressurized air (30 bar) to oxidize a variety of alcohols at 100°C. The reactions are highly selective and proceed in high yield, and in many cases the rate is limited mainly by the solubility of the alcohol in water.

  6. Translating an Edited Copy

    The kinetoplast of trypanosomes is an extranuclear DNA-containing organelle associated with the mitochondrion. Some messenger RNAs (mRNAs) of the kinetoplast are edited, which creates open reading frames for genes that otherwise encode nonsense mRNAs. However, the actual translation of these edited mRNAs—or, in fact, translation of any kinetoplast mRNA—has not been observed. Through sequencing the kinetoplast-encoded protein apocytochrome B, Horváth et al. (p. 1639) demonstrate translation of a kinetoplast-mitochondrion-edited mRNA. Translation of edited mRNA may represent a mechanism for mitochondrial gene regulation in trypanosomes.

  7. A Virus That Channels

    Potassium channels, once thought to occur only in eukaryotic cells, have recently been found in bacteria as well. Plugge et al. (p. 1641) now describe a gene in the chlorella virus PBCV-1 that encodes a K+ channel. This channel, named Kcv, does not seem to belong to any of the other K+ channel families described so far. However, it is a fully functional channel displaying several of the well-known characteristics of all the other K+ channels. It is also an extremely small protein and may thus be of help for the better understanding of the basic principles of K+ channel function and of ion channel function in general.

  8. Minding the Store

    Many cell functions are regulated through changes in the concentration of intracellular free calcium ([Ca2+]i). Often, stimuli that cause release of Ca2+ from intracellular stores later cause influx of Ca2+ through channels in the plasma membrane. However, the identity of these so-called store-operated channels (SOCs) in the plasma membrane and the mechanisms by which they are coupled to emptying of intracellular stores have remained unclear. Ma et al. (p. 1647; see the Perspective by Berridge et al.) took advantage of a new inhibitor of inositol trisphosphate (IP3) receptors to show that the IP3 receptor channels (which mediate release of Ca2+ from intracellular stores) are required for both activation and maintaining conductance of store-operated channels (SOCs) in the plasma membrane. The effects of the IP3 channel inhibitor are not the result of alterations in Ca2+ release. The results also distinguish the SOCs from TRP channels, which have been considered to be another candidate to mediate Ca2+ influx after depletion of intracellular stores.

  9. Monitoring Bacterial Motors

    New methods now allow biochemical studies to be performed on single cells rather than on populations of cells. Cluzel et al. (p. 1652) used optical spectroscopy to follow the output of the flagellar motor of individual bacteria in response to changes in the concentration of a chemotactic signaling molecule CheY phosphate (monitored through time-correlation fluorescence). The cell's response changed dramatically with CheY phosphate concentration because this signal appears to be amplified by the properties of the motor itself.

  10. Salmonella Survival Tactics

    Macrophages can destroy invading organisms such as Salmonella with reactive oxygen species produced by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Vazquez-Torres et al. (p. 1655) describe how virulent forms of Salmonella typhimurium can survive in macrophages—they secrete a defense system into the host vacuole that surrounds them. Somehow the defense system prevents the delivery of NADPH oxidase to the sites of invading Salmonella, which then go on to divide and cause disease.

  11. Seeking Damages

    Most of the energy deposited by ionizing radiation in living tissues is channeled into the production of secondary electrons with energies between 1 and 20 electron volts. Boudaïffa et al. (p. 1658; see the Perspective by Michael and O'Neill) show that these electrons, which are much lower in energy than the ionizing radiation and thus has been thought to be innocuous, can induce unexpectedly high levels of DNA damage in the form of single- and double-strand breaks. These results suggest that the traditional picture of radiolysis may need to be reevaluated.

  12. Stopping Ebola Virus

    Ebola virus causes a highly contagious, lethal hemorrhagic disease that has killed hundreds of people since it was first reported. There has been conflicting data regarding the ability of antibodies to provide immunity to the virus. Wilson et al. (p. 1664) identified protective monoclonal antibodies directed at three linear and two discontinuous epitopes on the glycoprotein of an Ebola virus. Mice were protected from the effects resulting from exposure to a mouse-adapted virus if they were treated 24 hours before exposure and even up to 2 days after challenge (a time when virus replication is occurring). Some of the antibodies tested were able to bind with all Ebola viruses known to cause disease.

  13. Winding Along the Wingless Pathway

    The wingless signaling pathway regulates cell fate decisions during embryogenesis of diverse organisms as well as cell proliferation in adult tissues. In a review, Peifer and Polakis (p. 1606) discuss two particularly active areas of investigation: (i) The critical role of regulated protein degradation in determining whether the wingless signaling pathway is ON or OFF; and (ii) New cytoskeletal targets of the pathway. A detailed map of the wingless pathway can be found at http://www.stke.org/.

  14. High-Pressure Feldspars

    Feldspars, which are alkali-rich aluminous silicates, are common in Earth's crust, but their high-pressure polymorphs have not been observed in nature. Gillet et al. (p. 1633) have now identified a high-pressure phase (about 23 gigapascals) of sodium-rich feldspar with the hollandite structure in the shocked melt veins of the Sixiangkou meteorite. They infer that the polymorph formed by a solid-state transformation or a rapid crystallization of the liquid under high pressure. For meteoritics, their results help to constrain the temperatures and pressures experienced by the material and to explain the fine-scaled structure and transformation mechanism of maskylenite, which is a ubiquitous feldspathic glass found in many meteorites. For terrestrial studies, their results provide information about the solubility of Na and K in the high-pressure polymorph that may carry Na, K, Al, and other trace elements into the mantle. [See the Perspective by Akaogi.]

  15. A Partner for the Dopamine Receptor

    Dopamine receptors have been intensively studied because of their central role in normal brain function and their involvement in a number of central nervous system diseases. Lezcano et al. (p. 1660) show that the D1 dopamine receptor interacts with a newly identified transmembrane protein named Calcyon. Ultrastructural analysis reveals a close association between Calcyon and a specific D1 receptor subpopulation. They further show that Calcyon is a potential G protein that mediates dopamine receptor-coupled signal transduction mechanisms. This finding may shed new light on the function of D1 receptors in the prefrontal cortex of the brain and their involvement in cognition and may also lead to new pharmacological approaches for the treatment of schizophrenia and other cognitive disorders.

  16. An Essential Part of the Checkpoint

    The Pin1 protein is a peptidyl-prolyl isomerase that is thought to function in control of the cell division cycle. However, its precise role in control of cell proliferation has been unclear. Winkler et al. (p. 1644) examined Pin1 function in Xenopus egg extracts. Extracts depleted of Pin1 entered mitosis more quickly than did controls. Normally, the presence of unreplicated DNA prevents progression of the cell cycle from G2 to M phase. However, extracts lacking Pin1 progressed into mitosis even when DNA replication was inhibited. Thus, although the mechanisms, by which Pin1 acts remain obscure, it appears that Pin1 is required for proper function of the DNA replication checkpoint in Xenopus eggs.

  17. Hepatitis C Virus, the E2 Envelope Protein, and

    In a Report (2 July), Taylor et al. demonstrated that the envelope protein E2 of genotype 1 of the hepatitis C virus (HCV) can inhibit the activity of PKR, an interferon-inducible protein kinase, in cultured cells. They linked this result to the similarity in genotype 1 of the PKR-eIF2α phosphorylation homology domain (PePHD)—a 12-amino acid sequence on the E2 protein—with that of the cellular PKR autophosphorylation site and the eIF2α phosphorylation site. “This interaction of E2 and PKR,” concluded Taylor et al., “may be one mechanism by which HCV circumvents the antiviral effect of interferon.” Abid et al. note, however, that HCV isolates from 15 patients they studied—eight infected with genotype 1 and seven with genotype 3—showed within-genotype variations in IFN resistance, despite identical or near-identical PePHD patterns in isolates from a given genotype. Taylor et al. respond that the E2-PKR interaction “cannot explain the sensitivity or resistance of different isolates within the same genotype,” and that HCV uses “a multi-pronged approach” to develop IFN resistance, of which the E2-PKR interaction is one element. The full text of these comments can be seen at www.sciencemag.org/cgi/content/full/287/5458/1555a

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