Editors' Choice

Science  19 Jun 2009:
Vol. 324, Issue 5934, pp. 1493
  1. Ecology

    Wetting One's Appetite

    1. Laura M. Zahn

    Ecological studies of food webs and their resources tend to focus on the limited availability of and competition for nutrients and energy. In some systems, however, water may exert an important influence on species interactions. McCluney and Sabo have investigated the impact of distinct water regimes on ecological systems in the San Pedro River in southern Arizona. In a field setting, they furnished cages containing field crickets with an ample supply of cottonwood and willow leaves, and they varied two factors: the presence/absence of wolf spiders (which prey on crickets) and mesic/xeric conditions. They found that when water was scarce, crickets consumed significantly more green leaves, rather than old litter, and experienced significantly higher mortality, presumably due to wolf spider predation, in comparison to cages lacking spiders. In contrast, in cases of rainfall or when water was provided, the cricket-spider interaction strength diminished almost to zero, suggesting that crickets were more important as a source of water than as nutrient. These data indicate that in some ecosystems, interactions between species can differ depending on water availability, and thus the local effects of global climate change—including derived aridification, droughts, and increases in precipitation—may alter food webs significantly.

    Ecology 90, 1463 (2009).

  2. Chemistry

    A Late Triple

    1. Jake Yeston
    CREDIT: SCHÖFFEL ET AL., ANGEW. CHEM. INT. ED. 48, 4734 (2009)

    Transition metals with comparatively few valence electrons, such as titanium and chromium, tend to form multiple bonds with carbon, oxygen, and nitrogen (N) atoms fairly easily. In contrast, late metals such as iridium (Ir) and platinum engage more rarely in this mode of bonding, an observation that has been justified by repulsive interactions between the ligand's lone pairs and residual d orbital electrons at the metal center. Schöffel et al. show that mild heating of an azide-substituted Ir complex in the solid state leads efficiently to N2 loss and resultant formation of a stable Ir-N triple bond. The compound was characterized crystallographically, and the observed bond length, coupled with indepth theoretical analysis, supports a formal bond order between 2 and 3. Reaction with hydrogen led to very clean direct reduction at nitrogen, forming an Ir amide complex that was also structurally characterized by x-ray diffraction. An isotopic labeling study confirmed H2 as the proton source.

    Angew. Chem. Int. Ed. 48, 4734 (2009).

  3. Virology

    Lessons from the Pros

    1. Helen Pickersgill

    Human cells contain tens of thousands of protein-encoding genes that are transcribed into a much larger numbers of mRNAs. Viruses, on the other hand, are far simpler, carrying with them only a handful of genes and proteins, yet they have developed countless ways of hijacking specific host cellular functions for their own benefit. Discovering these survival mechanisms often offers fascinating insights into normal host cell biology. Eukaryotes use sophisticated ways of regulating gene expression, including polyadenylating the 3′ end of mRNAs to enhance their stability for eventual translation into protein, and possibly also to promote mRNA degradation. Some herpesviruses, including Kaposi's sarcoma–associated herpesvirus (KSHV), manipulate host cells by promoting the widespread destruction of cellular mRNAs. KSHV achieves this via its Sox protein, and Lee and Glaunsinger show that human cells expressing the viral Sox protein contain mRNAs with unusually long poly(A) tails (hyperadenylation), which was mediated by the host enzyme poly(A) polymerase II. This effect of viral Sox was linked to its ability to accelerate mRNA turnover, suggesting that the virus induces host mRNA degradation by modulating poly(A) length.

    PLoS Biol. 7, e1000107 (2009).

  4. Chemistry

    Lining up for Photos

    1. Ian S. Osborne

    Transient diffraction techniques can be used in the gas phase to probe molecules in the midst of transformation, but structural information is limited by the random orientation of the sample. In contrast, static diffraction techniques applied to crystals that keep the constituent molecules well aligned can provide exquisite three-dimensional structures. Reckenthaeler et al. show that ultrafast optical methods can begin to bridge these two limiting cases. The authors use femtosecond laser pulses to dissociate gas phase diiodotetrafluoroethane molecules, creating a C2F4I ensemble briefly aligned on account of the laser polarization. Before the alignment is lost, a short pulse of electrons is fired through the sample, allowing the determination of transient molecular structure. Because the alignment persists for several picoseconds, the method may offer the opportunity to study a range of more complex molecular structures and dynamics.

    Phys. Rev. Lett. 102, 213001 (2009).