This Week in Science

Science  10 Oct 2003:
Vol. 302, Issue 5643, pp. 193
  1. The Organic Side of Mesoporous Silicates

    Mesoporous silicates have found use as templates for the creation of organic-inorganic nanocomposites. However, a limiting factor has been the fraction of organic material that could be linked to the silicate backbone without destroying the mesoporosity. Landskron et al. (p. 266) have found a route to form rings of alternating Si and CH2 groups to create a periodic mesoporous material with a much higher organic fraction. Films of this material have both a low dielectric constant and high mechanical stability and thus may find use in microelectronics.

  2. A Nonradical Approach to Oxidation

    The direct oxidation of organic molecules often proceeds through difficult-to-control radical pathways. Singlet oxygen, an excited form of oxygen in which the valence electrons are paired, reacts with organic molecules such as sulfides and phosphines through a nonradical pathway. Studies of these pathways should provide insight into developing other nonradical oxidants, but the initial species formed tend to be even more reactive than singlet oxygen itself. Ho et al. (p. 259; see the Perspective by Greer) now show that a phosphine with bulky substituents (o-methoxyphenyl groups) reacts with singlet oxygen to form a peroxy intermediate (a cyclic P-O-O ring) that can be characterized by nuclear magnetic resonance. This species oxidizes olefins to epoxides through a nonradical route.

  3. Fluorescence from a Moving Target

    Electron-transfer (ET) reactions are highly distance dependent, and thus conformational changes within an enzyme might leave their signature on the rates of individual steps. Complex multiexponential decays would be expected, but ensemble-average measurements might show this behavior simply because a heterogenous population is being probed. Yang et al. (p. 262; see the Perspective by Orrit) have followed the quenching of fluorescence of a flavin group in a flavin reductase and observed nonexponential decays from single molecules. These results support the idea that enzymes may dynamically convert between conformers that have different reactivities.

  4. Gene Interaction Arrays

    Although it is known that evolutionary conservation of gene sequence can provide clues to function, Stuart et al. (p. 249; see the Perspective by Quackenbush) now show that conservation of expression patterns can be an even more powerful tool. A set of more than 3000 human, fly, worm, and yeast microarrays revealed groups of genes that are coexpressed in multiple different species. The number and types of gene interactions provide insights into the evolution of gene function, whether genes act in a single pathway or have multiple functions, and how densely they are connected to other genes.

  5. Keeping in Time

    A functional pathway that connects the cell cycle and the circadian clock has long been suspected. Matsuo et al. (p. 255; see the Perspective by Schibler) have now identified a molecular link between these two major control systems that could explain how proliferating cells use information from the circadian clock to regulate the timing of cell division. In murine-regenerating liver, the expression of three key regulators of mitosis was controlled in a diurnal fashion. One of these factors, called WEE1, was directly regulated by two transcription factors that are core components of the mammalian circadian clock.

  6. Warming Up More Evenly

    If global warming were taking place, one would expect the troposphere to warm in a fashion consistent with the warming observed at Earth's surface. However, a reconstruction of middle-tropospheric temperatures based on microwave data from instruments flown on satellites has indicated that there has been little or no warming there, apparently contradicting a large body of measurements made at meteorological stations on the ground. Using a new analytical approach, Vinnikov and Grody (p. 269) find that the satellite microwave data contain the signature of a long-term warming trend in the troposphere as great or greater than that on the surface.

  7. An Animal Link in SARS

    The coronavirus SCoV that causes severe acute respiratory syndrome (SARS) has been thought to be an animal virus that recently crossed over to humans. Early cases of SARS occurred in Guangdong Province, China, among restaurant workers exposed to wild animals that are served as exotic foods. Guan et al. (p. 276; see the 5 September news story by Normile) tested for SCoV in animals at a retail market in Shenzhen. Civet cats, a raccoon dog, and a ferret badger showed evidence of infection with a coronavirus similar to the virus that causes SARS in humans; the human isolates show a 29-nucleotide deletion compared with the animal isolates. It is unclear whether these animals are the natural reservoir of the virus or are intermediate species in transmission.

  8. Trickle-Down Climate

    Recent observations have revealed that atmospheric circulation in the Southern Hemisphere has changed during the past several decades such that the westerly winds that encircle the southern polar cap have strengthened. This trend, which has been accompanied by a change in the tropospheric climate, is thought to be the consequence of lower stratospheric cooling caused primarily by photochemical ozone loss above Antarctica. Gillett and Thompson (p. 273; see the Perspective by Karoly) show that the observed trends can be simulated by a climate model perturbed only by documented stratospheric-ozone depletion. These results provide strong support for the hypothesis that stratospheric-ozone depletion is a critical factor causing climate change at Earth's surface, and that human activity has been an important part of this change.

  9. Shifting the Measuring Tape Before Cutting

    Mammalian introns can be both large and numerous, and so the process of cutting out of introns (splicing) must be both fast and accurate. Five RNA-protein complexes, known as U snRNPs, catalyze the two-step splicing reaction. The 5' or upstream end of the intron is first recognized by the U1 snRNP, followed by binding of the U4/U5/U6 snRNP. An intricate remodeling ensues, in which both the U1 and U4 snRNPs depart, with U6 snRNP taking over the chore of holding the 5' end of the intron in a receptive conformation that allows the first cut to take place. Chan et al. (p. 279) report that a subcomplex called Prp19 mediates a 5-nucleotide shift in how U6 snRNA base pairs with the 5' end of the intron as well as a dynamic opening and dissociation of the heptameric ring of Sm proteins, a structure common to all U snRNPs.

  10. Form and Function in the Inner Ear

    Zebrafish would be swimming in circles were it not for tiny crystals of calcium carbonate floating in their inner ears. These otoliths allow the inner ear to interpret movement and orientation in the physical world. Söllner et al. (p. 282; see the cover and the Perspective by Fekete) have now identified a protein, called Starmaker, that directs the formation of zebrafish otoliths such that they have the crystal lattice structure required for effective function. The Starmaker protein resembles in sequence a human protein that, when mutated, causes hearing loss and defects in teeth.

  11. Ancient Activities Retained

    During photosynthesis, the enzyme RuBisCO converts carbon dioxide into organic carbon. Intriguingly, several nonphotosynthetic bacteria include genes that code for proteins with sequence homology to RuBisCO. Ashida et al. (p. 286) show that a RuBisCO-like protein (RLP) from Bacillus subtilis catalyzes an essential reaction in the methionine salvage pathway. A growth defect caused by disruption of the RLP gene can be rescued by the gene for a photosynthetic RuBisCO. This finding establishes an evolutionary link between the archeal protein and photosynthetic RuBisCO.

  12. The Pain of Being Left Out

    Does the experience of pain associated with social exclusion engage the same brain structures (the anterior cingulate cortex) that mediate the affective responses to physical pain? Eisenberger et al. (p. 290; see the Perspective by Panksepp) tested the hypothesis by telling subjects that they would play a computer game with other individuals. They were then either passively excluded from the game while they watched (due to alleged technical problems), or were actively excluded from play after participating. Comparison of activity in the active exclusion versus inclusion conditions revealed greater activity in the anterior cingulate cortex, which correlated with subsequent self-reporting of distress during exclusion.

  13. Knowing When to Branch

    Neuronal axons form branches to establish precise connections with their targets, but branch control is not well understood. Colavita and Tessier-Lavigne (p. 293) have identified a subset of neurons in Caenorhabditis elegans that require a membrane protein called BAM-2 (branching abnormal) to stop formation of branches and stabilize their termination. Loss of BAM-2 allowed branches to overshoot their normal termination sites. BAM-2 shows sequence similarity to neurexins that are thought to control the stability of neuronal synapses.

  14. Seeing the Brain's Program at Work

    When the behavior of bees changes from working as nurses in the hive to foraging, gene expression patterns in their brains also change. Whitfield et al. (p. 296) studied gene expression in the brains of 60 individual honeybees. Microarray analyses led to identification of a set of 50 genes whose patterns of expression could be used to predict behavior.

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