This Week in Science

Science  31 Oct 1997:
Vol. 278, Issue 5339, pp. 777
  1. Mouse models for sickle cell anemia

    Animal models for human diseases have been valuable for understanding the disease and designing effective therapies. Two separate groups, Pásztyet al. (p. 876) and Ryan et al. (p. 873) have developed a strategy that resulted in a mouse model for sickle cell anemia (see the news story by Barinaga, p. 803). They first created mice that carried human sickle hemoglobin and then bred them with mice in which the mouse forms of α and β globin had been deleted. Progeny were identified that expressed only human hemoglobin and showed sickling of red blood cells, anemia, and organ pathologies that are characteristic of the human disease.

  2. Mesoporous metal films

    Mesoporous materials that contain nanometer-sized pores have received considerable attention recently. Most of these materials that have been made are ceramic oxides. Attard et al. (p. 838) now report the synthesis of mesoporous platinum films by electrodeposition of the metal from liquid-crystalline plating mixtures. Such materials could be used in applications that include catalysis, batteries, fuel cells, and sensors.

  3. Suddenly warmer

    The end of the Younger Dryas marked the abrupt (about 40-year) transition to warm climates in the Holocene; this transition has been studied closely as it provides information on the sensitivity of Earth's climate. Taylor et al. (p. 825) analyzed the GISP2 Greenland ice core, which provides a year-by-year account of the climate changes, and shows that this transition occurred in a series of steps each lasting less than 5 years. Some data imply that climate changes in the Arctic slightly follow changes at lower latitudes.

  4. Re-creating an earthquake

    The 1992 Landers earthquake in the Mojave Desert is one of the best-characterized recent events; surface deformation could be readily measured in the desert, and seismicity was monitored before and after this magnitude 7.3 earthquake. Olsen et al. (p. 834) used the slip and stress distribution derived from inverting the seismic data to re-create the initial stress distribution in the area before the earthquake and then forward-modeled the rupture in three dimensions. Their rupture model fits the general pattern of ground motions from seismic recordings but also shows a complex process that includes an increasing rupture velocity as the rupture approaches the surface, which was not predicted by simpler kinematic inversions.

  5. Quasi-periodicity in nonlinear optics

    Structures that repeat not on the basis of rational numbers, such as crystals, but that repeat on the basis of irrational ratios, are quasi-periodic. Zhu et al. (p. 843) show that the formation of layers of a nonlinear optical material, lithium tantalate, with a quasiperiodic (Fibonacci) sequence is useful in generating third-harmonics of laser light. The availability of more wave vectors in such a lattice allows coupling of two processes, frequency doubling and frequency adding, so that the normally weak third harmonics can be generated efficiently.

  6. Copper chaperone in the cell

    Certain enzymes in mammalian cells require metals such as copper as cofactors. However, free copper can be toxic to the cell and propagate auto-oxidation of lipids, proteins, or nucleic acids. Pufahl et al. (p. 853; see the Perspective by Valentine and Gralla, p. 817) describe the function of a copper chaperone protein called Atx1, which receives copper from an uptake protein in the membrane and then binds it in an unusual three-coordinate state as Cu(I). The Atx1 protein then carries the copper to its destination where Atx1 interacts with the vesicular protein Ccc2. The Cu(I) ion is passed to Ccc2 and ultimately to the multicopper oxidase Fet3, the essential enzyme in the high-affinity iron uptake system. This system allows the cell to supply copper to key enzymes without the release of copper ions directly into the cytoplasm.

  7. Aerosols and smog production

    Photochemical smog, characterized by high ground-level ozone and nitrogen oxide levels, depends partly on the intensity of solar ultraviolet radiation. Atmospheric aerosols scatter or absorb ultraviolet light, but a quantitative analysis of this effect on smog formation has been lacking. Numerical modeling by Dickerson et al. (p. 827) of observations of aerosols, radiation, and photochemistry indicate that smog production is accelerated by ultraviolet-scattering aerosols and inhibited by ultraviolet-absorbing aerosols.

  8. Responding indirectly

    Previous assessments of global terrestrial responses to climate change have focused on direct responses to change in carbon dioxide or temperature. These near-instantaneous responses include, for example, the effects of increased temperature on photosynthesis and respiration. However, field ecologists have repeatedly suggested that indirect responses, such as feedbacks through soil water storage or nutrient cycling, may be more important. Braswell et al. (p. 870; see the news story by Williams, p. 802) offer a global assessment of direct versus indirect effects, and demonstrate the importance of indirect effects. The results also provide evidence at the global scale for major differences between biomes in both the direction and strength of these indirect effects: Large-scale modification of global ecosystems could alter the response of the biosphere to climate change.

  9. Cytokines and NF-KB

    The transcription factor NF-κB is critical for regulation of gene transcription in cells of the immune system. Two reports discuss identification of a new component of a regulatory pathway that controls the activity of NF-κB in response to cytokines like tumor necrosis factor-α or interleukin-1 (see the Perspective by Maniatis, p. 818). NF-κB is held in an inactive state by the protein IκB, and interaction of the two proteins is controlled by phosphorylation of IκB. A protein kinase (IκB kinase or IKK-1) that participates in this regulation has been recently described. Mercurio et al. (p. 860) and Woronicz et al. (p. 866) now report isolation and characterization of a second member of the IKK family (IKK-2). The two IKKs interact with each other and with another protein kinase, NIK, in a large protein complex.

  10. The shape of iron in the core

    Earth's interior is composed of an iron-rich liquid outer core and solid inner core, whose well-known bulk properties help us understand the geodynamo and mantle convection. However, a determination of the structure of the iron phase in the inner core would improve our understanding of core-coupled dynamic mechanisms at work in Earth's interior that eventually effect the planet's surface. Andrault et al. took advantage of the improved intensity and resolution of x-ray beams produced by the third-generation European Synchrotron Radiation Facility to perform in situ angle-dispersive x-ray diffraction measurements on iron at pressures between 30 to 100 gigapascals and temperatures as high as 2350 kelvin. Iron undergoes a phase transformation at high temperatures and pressures to an orthorhombic structure due to a shift along the basal plane of the iron lattice. [See the Perspective by Anderson.]

  11. Sensitive silicon sensors

    Porous silicon, well known for its electroluminescence, has also been put to work as a biosensor. Lin et al. created optical interferometers of porous silicon, and these thin films were derivatized so that they could bind small organic molecules, small DNA oligonucleotides, or proteins. Binding changed the refractive index of the semiconducting silicon, which induced wavelength shifts in the Fabry-Perot fringes of reflected visible light. The effect is sufficiently sensitive that pico- to femtomolar concentrations of analytes could be detected. [See the news story by Service.]

  12. Electron transfer simplified

    Although strongly exothermic electron transfer reactions initiated by photoexcitation can be understood relatively well with existing theories, rate constants for reactions that have low exothermicity and that occur in the dark have been difficult to reproduce within these theoretical frameworks, even when tunneling is invoked to achieve better agreement between experiment and theory. Nelsen et al. show that by making a relatively small change to the adiabatic energy surfaces, the intramolecular energy transfer rate constants can be calculated accurately for a range of organic compounds without explicitly invoking tunneling terms

  13. Structural studies of HIV-1 capsid dimerization

    The capsid protein of human immunodeficiency virus-type 1 (HIV-1) not only forms part of the viral structure but is also essential to roles in viral entry, uncoating, and replication. Gamble et al. present the crystal structure of carboxyl-terminal domain of capsid, which is essential for dimerization and that contains the major homology region (MHR), a conserved stretch of 20 amino acids in all known onco- and lentiviruses. The MHR region is not part of the dimer interface but instead helps form an intricate network of hydrogen bonds that interconnect its extended amino-terminal strand with two helices. A model of the full capsid protein is presented based on this structure in tandem with previously determined structures of the amino-terminal domain

  14. Nanomoves of microtubules

    Recent technical advances have allowed physicists to begin examining the dynamic properties of biological macromolecules, such as the motor protein kinesin and the structural protein titin. Dogterom and Yurke turned their sights toward an assembly of macromolecules, the microtubule, and describe the relation between the velocity of extension (addition of tubulin monomers) and an opposing force (produced when the growing

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