This Week in Science

Science  20 Jul 2001:
Vol. 293, Issue 5529, pp. 389
  1. Carbon Swings in the Pacific

    The cycles of El Niño and La Niña can have large impacts on the global carbon cycle, particularly in new production—that is, the marine productivity which is supported by nutrients imported into a given region, as opposed to that which occurs by local nutrient recycling. Turk et al. (p. 471) combine satellite measurements of sea surface height, ship and buoy measurements of isotherm depth, and local estimates of new production to infer equatorial Pacific basin-wide estimates of new production for the years 1992 to 1999. This period included an extremely strong El Niño and a moderately strong La Niña. Carbon export varied by a factor of 3 between these episodes.

    CREDIT: TURK ET AL.
  2. Crystalline Oxides on Silicon

    As the size of transistors decreases, the need increases for a replacement for amorphous silicon oxide as the insulator in these devices. One alternative is to grow crystalline oxides on silicon, which should avoid the steric hindrance and bond-coordination problems inherent in amorphous oxides. McKee et al. (p. 468) demonstrate commensurate growth of cubic alkaline earth and perovskite oxides on silicon that results in high-quality interface regions with extremely low defect densities. The ability to manipulate the dielectric displacement and the inversion charge at the interface may lead to additional device functionality.

  3. Measuring a Polymer's Reach

    Most measures of polymer chains in solution provide insight into their average conformation, but fluctuations can produce excursions that change the overall shape and end-to-end length of the chain over time. Jeppesen et al. (p. 465; see the Perspective by Russell) attached polyethylene glycol, labeled at its free end with biotin, to one surface in surface force apparatus and labeled the opposing surface with its receptor, strepavidin. By determining the capture probability of the free biotin end as a function of distance between the surfaces, they show that rare highly extended conformations of the polymer play a key role in the binding process.

  4. Staying in Shape

    Many proteins form relatively compact molten-globule intermediates under mildly denaturing conditions, but high concentrations of denaturant proteins would be expected to produce an ensemble of conformations that approach statistical randomness. Shortle and Ackerman (p. 487) used nuclear magnetic spectroscopy to measure residual dipolar couplings in denatured forms of staphylococcal nuclease. Long-range order, in which chain segments retain their same relative orientations, persisted even in 8 molar urea.

  5. Leggy Old Crustacean

    In the hamlet of Comley, Shropshire, England, Siveter et al. (p. 479; see the Perspective by Fortey) have found a well-preserved crustacean in a temporary trench dug into Lower Cambrian limestone formations. Two specimens of the soft anatomy of these phosphatocopid arthropods are protected within partial to nearly complete carapaces and provide exquisite detail about the body and limbs in three dimensions. These early Cambrian specimens should help paleontologists decipher whether Crustacea evolved in the Precambrian or radiated more rapidly during the Cambrian explosion.

  6. Warmer, Stormier Weather in Store

    Average global temperatures will increase during the next century, largely because of anthropogenic modifications of the atmosphere, but by how much· Wigley and Raper (p. 451) have made probabilistic projections of future warming trends. They conclude that the most likely future is one in which warming will be closer to the middle of current estimates, rather than at the high or low extremes of the range. One consequence of global warming could be an increase in storminess. Goldenberg et al. (p. 474; see the cover and the Perspective by Bengtsson) report an increase in hurricane activity in the North Atlantic since 1995. They examined the meteorological record of tropical cyclones since 1944, and by comparing it to concurrent measurements of sea surface temperature and atmospheric vertical shear (two key factors in hurricane formation), present mechanistic support for the observed recent increase in the frequency of hurricanes there.

  7. SNP'ing Through Population Heterogeneity

    Analysis of genetic variation could revolutionize studies of disease susceptibility and allow treatment of disease to be tailored to the individual. Stephens et al. (p. 489) have identified single nucleotide polymorphisms (SNPs) from 313 genes in 82 individuals of different ancestral backgrounds. The SNPs were characterized according to frequency, distribution among populations and functional genomic regions, potential functional consequences, inferred mutation pattern, linkage, and organization within each chromosome in each individual (haplotype). The strength of the genetic association of pairs of SNPs (linkage disequilibrium), which is important in the identification of disease-related genes, could not be readily predicted from examining individual genes or genomic regions. Generally, haplotypes were more informative as genetic markers than the SNPs contained within a gene.

  8. Redox Around the Clock

    Circadian rhythms are controlled by an evolutionarily conserved transcriptional feedback system whose activity fluctuates as a function of the 24-hour light-dark cycle. Extrinsic factors, such as changes in food intake, can advance or delay the circadian clock, but the mechanism by which this “entrainment” occurs remains unclear. A key regulator of circadian rhythms, Clock, is expressed in the suprachiasmatic nucleus (the brain region regarded as the master pacemaker) and regulates the expression of genes encoding other clock components. Reick et al. (p. 506) and Rutter et al. (p. 510; see Perspective by Schibler et al.) show that the NPAS2 transcription factor performs a function similar to Clock in the mammalian forebrain and that the DNA binding activity of both these transcription factors in vitro is regulated by the redox state of NAD (nicotinamide adenine dinucleotide) cofactors. Because changes in food intake are associated with changes in cellular redox state, the authors propose that redox control of Clock and NPAS2 activity may explain how food and other extrinsic factors entrain the molecular clock.

    Figure
    CREDIT: TURK ET AL.
  9. The Benefits of Huntingtin

    The huntingtin protein is mutated in Huntington's disease, a fatal neurodegenerative disorder that strikes in middle age. It has been presumed that mutant huntingtin becomes toxic to neurons by forming aggregates with itself and with other intracellular proteins. Zuccato et al. (p. 445; see the Perspective by Trottier and Mandel) show that the loss of huntingtin's normal function results in death of striatal neurons in the brain. Wild-type huntingtin boosts the production of brain-derived neurotrophic factor, which striatal neurons require for survival.

  10. Profile of a Killer

    The international increase in antibiotic-resistant outbreaks of Streptococcus pneumoniae will only add to millions of deaths caused by this pathogen from pneumonia, meningitis, and other illnesses. Tettelin et al. (p. 498; see the news story by Ferber) have sequenced this pathogen's genome and found several clues into its pathogenesis and possible vulnerable points. The high percentage of sugar transporters (higher than any other sequenced prokaryote) suggests that it may occupy a distinct microenvironment within the respiratory tract. A motif potentially related to cell adhesion, large numbers of insertion sequences, and a possible targeting signal for surface-associated proteins were also observed.

  11. Glutamate Receptor Clusters in Spontaneous Transmitter Release

    Clues into the functional significance of spontaneous miniature synaptic potentials (minis), which result from the “random” fusion of synaptic vesicles at nerve terminals, have been revealed by Saitoe et al. (p. 514; see the Perspective by Verstreken and Bellen), who examined minis in mutant Drosophila with known defects in presynaptic function. Minis, as well as regulated neurotransmitter release, only occurred in the neuromuscular junctions of flies that possessed normal clusters of glutamate receptors in postsynaptic cells. The developmental clustering of glutamate receptors may be linked to spontaneous vesicle release as a prequel to functional synapse formation.

  12. Lighting an Electron's Path

    Electron transfer between a solvated ion, Na, and its solvent has now been controlled with femtosecond laser pulses. Sodium metal can dissolve in organic solvents such as tetrahydrofuran (THF) by disproportionation to form Na+ and Na, and if complexation agents such as crown ethers are present, Na species will remain in solution. Martini et al. (p. 462; see the Perspective by Bardeen) studied the photoexcitation of Na in THF, which can either produce a solvated electron and neutral sodium or back-react to reform the ion. This process depends on solvent motion, and they found that light pulses could be used to move the electron between a location next to the Na anion or to an adjacent cavity in the solvent. By changing the starting environment for the electron, subsequent laser pulses could be used to select for the solvated electron or for the anion.

  13. Dining Together

    The anaerobic oxidation of methane is well known, but little is known about the organisms that mediate methane consumption. Orphan et al. (p. see the news story by Zimmer); have used a combination of genetic identification and stable isotope analysis in situ to reveal that colonies of hydrogen-consuming, sulfate-reducing bacteria form a shell around clusters of methanotrophic archaea in sediments obtained from methane seeps off the Californian coast. The results suggest that methane-derived intermediates within the syntrophic assemblages, such as acetate or carbon dioxide, as well as hydrogen, are transferred from the methane-consuming archaea to the sulfate-reducing bacterial partners.