This Week in Science

Science  09 Aug 2002:
Vol. 297, Issue 5583, pp. 893
  1. In Brevia

    A captive New Caledonian crow, observed by Weir et al. (p. 981), spontaneously and then repeatedly bent a piece of wire into a hook for use in a task requiring a hooked tool.

  2. They've Got the Quantum Beat

    The measurements of the dipole moment of molecules in high vibrational states might seem esoteric, but for water, these values are crucial for developing an accurate picture of the water absorption spectra crucial for atmospheric energy balances. Measurements of the Stark effect have been used previously to obtain ground-state and low-lying excited-state dipole moments. Callegari et al. (p. 993; see the Perspective by Bernath) now use three different lasers and a Stark field simultaneously to determine permanent and transition dipole moments through quantum beat spectroscopy of water molecules with 4, 5, or 8 quanta of excitation in their O-H stretching vibration. These values deviate systematically from the best theoretical estimates and will serve as benchmarks for future calculations of potential energy and dipole moment surfaces.

  3. Extended Actuator Lifetime

    Conducting polymers have many electrochemical applications, such as batteries and light-emitting diodes, but their performance tends to degrade rather rapidly with repeated cycles of charging and discharging. The problem is often not the conducting polymer itself but the degradation of the electrolyte in which the polymer is immersed or embedded. Lu et al. (p. 983) show that the combined approach of improving the conducting polymer and using ionic liquids is an effective route for achieving stable electrochemical devices.

  4. DNA Obstacle Course

    For a polymer chain to move from one position to another, all of the segments need to shift position, either in a sequential or cooperative fashion, or some mixture of both. Confining the motion to two dimensions simplifies the picture somewhat because it limits the chains' ability to entangle and also allows for the direct visualization of individual chain motion. Nykypanchuk et al. (p. 987) used a colloidal templating process to create a series of spherical cavities interconnected via circular holes. Using a fluorescent dye, they were able to watch the motion of linear DNA as it jumped from cavity to cavity. Under these conditions, entropic barriers controlled the chain motion.

  5. When Many Trees Fall in the Forest

    The rate of tropical deforestation bears on issues in tropical ecology, biodiversity, and the sustainable use of the biosphere, and more reliable estimates of tropical deforestation rates are needed to complete models of the global carbon cycle and to determine the magnitude of the “missing” carbon sink. Achard et al. (p. 999; see the news story by Kaiser) have now determined rates of tropical deforestation from satellite imagery and improved statistical sampling strategy. They find that tropical humid forests are disappearing at a rate 23% lower than that of the best previous estimates. Despite this apparent bit of good news, the bad news is that humid tropical forests are disappearing at a rate of 5.8 million hectares (nearly twice the area of Belgium) a year, and an additional 2.3 million hectares per year are being degraded.

  6. Duplicates Within the Human Genome

    Compared to other sequenced animal genomes, the human genome is enriched for large, segmental duplications that arose less than 40 million years ago. By comparing the two versions of the human genome sequence available, Bailey et al. (p. 1003; see the Perspective by Lynch) identified regions that are overrepresented within a random set of fragments and thus are legitimate duplications within the genome. These duplications are distributed nonrandomly among human chromosomes. They identified 169 regions as possible hot spots of genomic rearrangement that provide a set of candidates for identification of human genetic diseases associated with unequal recombination between duplications as well as the genetic rearrangements associated with primate evolution. The study is also providing a valuable resource for generating a finished version of the human genome sequence.

  7. Not Just Space Eggs

    Egg-type structures consisting of a core of one phase of an aluminum-indium alloy and an outer portion of the other phase have been produced in fine, rapidly solidified powders grown under microgravity conditions. Wang et al. (p. 990) now show that such materials can also be grown on Earth if there is a miscibility gap in the liquid state of the alloy phase diagram, in this case for iron-copper-based alloys. Even under rapid cooling, the difference in the temperature dependence of the interfacial energy causes Marangoni motion and causes the minor liquid component to form the core of the egg-type particles.

  8. Black Sea Reef Builders

    The recent discovery of large microbially generated reefs in the Black Sea associated with methane seeps along the Crimean peninsula has implications that may lead to a reassessment of the evolution of metabolism as well as the geochemical and atmospheric history of the early Earth. Michaelis et al. (p. 1013) show that the isotopically light carbonate reefs are built by consortia of anaerobic, methane-oxidizing microorganisms that reach extremely high biomass and that contribute substantially to carbonate deposition under anoxic conditions. Previously, the isotopic signatures for methane oxidation have been interpreted as a sign of aerobic methanotrophy and an early oxygenation of the Earth's atmosphere. These new findings suggest that anaerobic conditions could have prevailed on the early Earth and that the anaerobic oxidation of methane by sulfate, accompanied by carbonate precipitation under alkaline conditions, could have occurred on a major scale.

  9. Holistic Cell Signaling

    Mitogen-activated protein (MAP) kinases 1 and 2 are important regulators of many cellular processes. Not surprisingly then, they are subject to complicated regulatory circuits that both feed forward to favor activation of the kinases and feed back by stimulating enzymes that lead to inactivation of the MAP kinases. MAP kinase phosphatase (MKP), for example, dephosphorylates—and can thus inactivate—MAP kinases 1 and 2. However, MKP must be considered in the context of competing feedback loops and other inhibitory phosphatases. Bhalla et al. (p. 1018; see the Perspective by Ingolia and Murray) use a combination of experimental analysis with computational analysis and modeling to propose an unexpected role for MKP. Their studies indicate that MKP is not a major determinant of the acute activity of MAP kinases in growth factor-stimulated cells. Rather, increased activity of MKP seems to change the properties of the regulatory network such that strong stimuli that should have produced sustained activation of the MAP kinases only produces a short-term activation of those enzymes.

  10. Controlling Telomerase on Telomeres

    Telomeres are found at the tips of chromosomes, where they help solve the end-replication problem as well as prevent potentially lethal end-to-end fusion of chromosomes. Telomeric DNA consists of simple repeats, and telomere length is maintained by the telomerase enzyme, which is comprised of four components, Est1p, Est2p, and Est3p, and TLC1 RNA. The enzyme complex has been thought to be recruited to the telomeres during S-phase by Cdc13p, a protein that binds single-stranded DNA. Working in yeast, Taggart et al. (p. 1023) now show that telomerase components are associated with the telomeres even in the presence of mutated, inactive Cdc13p, and thus recruitment cannot explain telomerase regulation. Rather, the core telomerase enzyme, Est2p-TLC1 RNA, is associated with the telomeres prior to S-phase, and is then activated in late S-phase by the binding of Est1p.

  11. Jack of All Cell Division

    The highly conserved origin recognition complex (ORC) mediates initiation of replication of the genome in eukaryotes, but ORC functions in other cellular processes such as gene silencing and heterochromatin formation. Orc6, the smallest subunit in human cells, has previously been shown to bind to chromatin throughout the cell cycle. Prasanth et al. (p. 1026) now show that during mitosis, Orc6 is also found at the kinetochore, at the plane of cell division, and at the midbody of dividing cells. A diminution of Orc6 function produced with small intermediate RNAs resulted in a complex phenotype whose characteristics included increases in polyploidy, aberrant mitoses, cells with multipolar spindles, and the failure of chromosomes to align at the metaphase plate. Thus, Orc6 functions in a wide range of cell division activities, including replication, chromosome segregation, and cytokinesis.

  12. Maintaining Immunity

    Phosphoinositide 3-kinase activity regulates many cell processes across many cell types. There are three isoforms of its catalytic subunit p110, but their specificity has not been clear. Okkenhaug et al. (p. 1031) generated a mouse that expresses an inactive form of p110 and observed compromised B and T cell immune function. The study reveals a highly selective, nonredundant role for this isoform in lymphocyte antigen receptor signaling as well as a drug-development target.

  13. Clustering Around Niobium

    Heteropolyanions (HPAs) are large cluster anions formed by the assembly of 12 to 30 octahedra in which oxygen atoms surround a metal center. These anions have found several applications, such as in catalysis and environmental cleanup, but to date are based on molybdenum, vanadium, or tungsten. Attempts to replicate this chemistry, which requires basic conditions, are usually unsuccessful with niobium, which tends to form the Lindquist anion [Nb6O19]8− instead. Nyman et al. (p. 996) now show that under hydrothermal conditions, both extended solids and clusters containing Nb HPAs can be synthesized.

  14. Predicting Splicing Phenotypes

    A combination of computational and experimental approaches has been used to identify exonic splicing enhancers (ESEs), which increase the joining of exons to build messenger RNA. Fairbrother et al. (p. 1007) started with fundamental attributes of ESEs to derive a set of hexamer candidates from human genomic sequences. Cluster analysis of more than 200 hexamers resulted in the identification of 10 distinct groups of hexamer motifs. Of these, five were different from known ESEs. Experimental testing revealed that all of the groups possessed ESE activity, albeit at different levels. Mutation of the individual ESEs that had been identified resulted in decreased ESE activity. A group of mutations that cause exon skipping in the human HPRT gene in vivo were found with sequences that fit within the authors' models of ESEs.

  15. C332,652H492,388N98,245O131,196P7501S2340

    Infectious poliovirus has been assembled through a process in which the genome sequence served only as the blueprint. Cello et al. (p. 1016) used a combination of organic synthesis, recombinant DNA methods, and an established system of replication in a cell-free system to produce a virus that is neurovirulent in mice. If viruses no longer found in nature can be reconstituted from organic precursors, then this demonstration has important implications concerning the eradication of poliovirus.

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