This Week in Science

Science  18 Oct 2002:
Vol. 298, Issue 5593, pp. 491
  1. In Brevia

    The stable carbon isotopic composition of a stalagmite from Belize determined by Frappier et al. (p. 565) displays a strong correlation to the El Niño-Southern Oscillation, which suggests that the surrounding ecosystem may be acting as a climate signal amplifier.

  2. Satellite Disk Drives

    The Galilean satellites Io, Europa, Ganymede, and Callisto accreted in the disk of debris developed during the formation of Jupiter. Io, Europa, and Ganymede are currently synchronized in their orbital patterns, which indicates that initially random orbits have migrated into a stable system. Peale and Lee (p. 593) show that the orbital patterns were stabilized by disk-satellite interactions. Thus, the orbital patterns are primordial and do not require unusual tidal torques from Jupiter.

  3. Flow-Through Integrated Circuits

    In an electronic integrated circuit, all of the necessary components are fabricated onto a single semiconductor, which eliminates the need for manual assembly of the individual transistors, capacitors, and resistors. Thorsen et al. (p. 580; see the cover) have now fabricated an analog in a microfluidics system with a set of individually addressable microvalves. Such a system can act as a fluidic random-access memory and can also be used as a series of microreactors in which each reactor can be individually controlled.

  4. Peering into the Vortex Core

    The existence of magnetic vortex cores was predicted almost 40 years ago, but they have only recently been observed experimentally. However, the rather low spatial resolution of the magnetic surface probes could not resolve the spin structure within the vortex core. Wachowiak et al. (p. 577; see the Perspective by Miltat and Thiaville), using a spin-polarized scanning tunneling microscope, now provide such details. They verify the long-standing predictions that the width of the core is dependent on the stray field from the out-of-plane magnetization and can be increased or reduced by the application of a magnetic field parallel or antiparallel to the core magnetization, respectively.

  5. African Ice

    Ice core records are generally associated with high latitudes, but low-latitude glaciers are now providing glimpses into climate in those regions for which we have poorer records of recent climate. One such place is tropical east Africa. Thompson et al. (p. 589; see the Perspective by Gasse and the news story by Krajick) report results from cores drilled in the ice fields on the top of Mount Kilimanjaro, Tanzania. They analyzed the oxygen isotopic composition, dust content, and major ion abundance of six cores, the oldest of which extends back to approximately 12,000 years before present, to create a high-resolution record of the Holocene climate in this region.

  6. We're JAMMing

    A protein motif, termed JAMM, has been identified that appears to be responsible for encoding a metallo-isopeptidase activity important in cleaving either ubiquitin or ubiquitin-like Nedd8 moieties from proteins (see the Perspective by Hochstrasser). Cope et al. (p. 608) show that in the COP9 signalosome, the JAMM motif acts to deneddylate substrates, such as those that are important in eye development. Verma et al. (p. 611) show that in the proteasome lid subcomplex, the JAMM motif is important in cleaving ubiquitin from a variety of substrates, and that inactivation of the JAMM motif is lethal in yeast.

  7. Model Grasslands

    The soil biota provides many services, including soil fertility, bioremediation, control of soil structure, and habitat for vertebrates. Information on how disturbances, such as land degradation, erosion, and elevated CO2, affect the soil community and the ecosystem processes they control is important for global sustainability. However, investigating these relations has been a challenge, given the complexity of soil habitat and its biodiversity and the density and abundance of soil-dwelling organisms. Bradford et al. (p. 615) manipulated biodiversity by changing the size of the organisms introduced into soil microcosms and found marked responses in the short term in plant community composition and other variables. Strikingly, there was no change in two major ecosystem parameters generally measured for aboveground (and global) ecology—total ecosystem carbon balance and net primary production.

  8. Hot Spot

    Microwave radiation, long used for heating and drying, can now be used for drilling nonconductive materials such as ceramics, glass, concrete, and silicates. Jerby et al. (p. 587; see the news story by Sincell) describe the design and operation of a drill that focuses the radiation, creating a localized hot spot at the subsurface below the drill tip. As many materials better absorb microwave radiation as the temperature increases, a runaway reaction occurs at the drill tip, which can be slowly pushed through the molten material. The drill has the advantage that it is both quiet and creates little mess, and may fill a niche where conventional mechanical drills or laser drills are not ideal.

    CREDIT: JERBY ET AL.
  9. Biosilica Via Highly Phosphorylated Peptides

    The cell walls of diatoms—unicellular algae that are the greatest primary producers of the ocean—are made from intricately patterned biosilica. Highly modified peptides called silaffins, which have been extracted from diatom biosilica, can precipitate nanometer-scale silica spheres under appropriate conditions. Kröger et al. (p. 584; see the Perspective by Wetherbee) now show that extraction under milder conditions preserves the native silaffins, which are highly phosphorylated. The native silaffins form a composite with silica that is likely to play a key role in the in vivo formation of biosilica by diatoms.

  10. A Copper Surprise in CO Reduction

    Acetogenic bacteria can use carbon dioxide (CO2) as their sole carbon source. Key to this ability is the bifunctional enzyme, carbon monoxide dehydrogenase/acetyl coenzyme A synthase (CODH/ACS). In the CODH subunit, CO2 is reduced to CO, while in the ACS subunit the CO is combined with a methyl group and coenzyme A (CoA) to form acetyl-CoA. Doukov et al. (p. 567; see the Perspective by Peters) have solved the structure of CODH/ACS from Moorella thermoacetica at 2.2 angstroms (Å). Focusing on the metal cluster where acetyl-CoA is assembled (C-cluster), they find an [Fe4S4] cubane bridged to not to just a Ni atom but to a Cu-Ni binuclear site. The presence of Cu in CODH/ACS enzymes has not been reported previously, and, based on the binuclear center, the authors propose a binuclear catalytic mechanism. A long channel (138 Å) provides a passage for CO and prevents it from being released into solution.

    CREDIT: DOUKOV ET AL.
  11. Developing in the Shadows

    Visual inputs from right and left eye are segregated in the brain's visual cortex into ocular dominance columns. Although evidence suggests that ocular dominance columns form only in response to neuronal activity, other results have also suggested that they may form in response to intrinsic developmental cues. Now, taking advantage of a naturally occurring imbalance in visual inputs, Adams and Horton (p. 572) show that asymmetric visual deprivation is a normal part of development and that formation of ocular dominance columns is affected. The blood vessels that course over the retina shade each eye's retina in unique patterns. In the brain of the squirrel monkey, representations of these visual asymmetries are reflected in the ocular dominance columns. Compared with macaques and humans, the squirrel monkey's general ocular dominance columns are rather smaller and less well delineated. This difference may account for why the asymmetries of visual input caused by retinal blood vessels have a more apparent affect on the organization of the squirrel monkey's visual cortex.

  12. Discerning the Cause of the Pause

    The written word is readily identified by the blank spaces surrounding it. How do we learn to identify where one spoken word ends and the next begins? A previous study of infants has suggested that words can be identified by taking a low probability transition between syllables as a word break; that is, two syllables that rarely occur in order are more likely to be the end of one word and the start of the next. Another previous study suggests that infants can generalize from experience with a structured set of syllables and segment unfamiliar syllables into the same word structure. Peña et al. (p. 604; see the Perspective by Seidenberg et al.) have examined both kinds of pattern recognition in adults and found that generalization can be induced by a subliminal gap of 25 milliseconds between words, but that increased exposure to a continuous stream of syllables does not result in learning.

  13. The Signature of Stem Cells

    Are there genes that characterize various sets of stem cells? Ivanova et al. (p. 601) and Ramalho-Santos et al. (p. 597) used transcriptional profiling of mammalian embryonic and adult stem cells to identify genes that are common among hematopoietic stem cells, embryonic stem cells, and neural stem cells. These subsets of genes may provide stem cells with the ability to self-renew, to generate differentiated cells, or to do both, and hence represent, according to the authors, “stemness” or a “stem cell molecular signature.”