Editors' Choice

Science  21 May 2010:
Vol. 328, Issue 5981, pp. 955
  1. Molecular Biology

    Refusing to Be Silenced

    1. Guy Riddihough
    CREDIT: AZEVEDO ET AL., GENES DEV. 24, 904 (2010)

    Pathogens are in a continual evolutionary struggle with their hosts—each side exploits new avenues of attack while simultaneously patching breaches in its defenses. A major defense mechanism used by plants against viral infection involves the RNA interference (RNAi) pathway, whereby small RNAs cleaved from the virus are subsequently used to target for destruction any virally produced RNAs. At the same time, viruses have developed proteins (or to be more accurate, modified existing ones) that subvert this antiviral RNAi system.

    Azevedo et al. find that the capsid protein P38 of the turnip crinkle RNA virus (TCV) has acquired two glycine-tryptophan (GW) repeat motifs. These motifs are commonly found in proteins that bind to and promote the function of Argonaute (Ago) proteins in the RNAi pathway. P38 binds to the plant Ago1 though its GW motifs, probably preventing Ago1 from interacting with other RNAi pathway proteins; this probably involves the ability of P38 to multimerize (hexamers are shown at left)—intrinsic to its role as a capsid protein. The suppression of Ago1 also represses the action of microRNAs, which bind to and act though Ago1. One such miRNA, miR162, normally acts to suppress the enzyme Dicer-like 1 (DCL1), which suppresses two other Dicer family members, DCL2 and DCL3, both of which are critical for cleaving small RNAs from TCV for targeting by the RNAi pathway. Thus, suppressing Ago1 miRNA function allows DCL1 activity to increase, which reduces DCL2 and DCL3 levels, which in turn blunts the ability of the plant to capture the targeting RNAs from the virus.

    Genes Dev. 24, 904 (2010).

  2. Cell Biology

    Of Mice and Ricin

    1. Stella M. Hurtley

    Certain bacterial and plant toxins gain access to their intracellular targets by taking advantage of existing intracellular transport machinery. The plant toxin ricin follows the retrograde transport route from the cell surface via endosomes and the Golgi complex to the endoplasmic reticulum en route to the cytosol, where it binds to and inactivates its target, ribosomal RNA. Ricin represents a potential bioterrorism weapon, for which there are no widely available treatments. Stechmann et al. screened for small-molecule inhibitors that could protect human lung cells from ricin and two similar bacterial toxins. Two of the identified compounds, termed Retro-1 and Retro-2, inhibited the transport step from endosomes to the Golgi. One of these compounds, Retro-2, was even able to protect mice from an otherwise lethal exposure to ricin.

    Cell 141, 231 (2010).

  3. Physics

    Activating Quantum Implants

    1. Ian S. Osborne

    Diamonds typically contain many impurities and defects, which affect their sparkle and color. One such defect, the negatively charged nitrogen vacancy (NV) center, is effectively an isolated single spin. Clever manipulation of such single-spin NV centers provides a means for the individual spins to communicate with each other quantum-mechanically, as well as act as a memory wherein bits of quantum information can be stored and retrieved. Instead of using naturally occurring NV centers, applications will require a designed array of artificially implanted defects. However, not all NV centers are active. Overcoming this limitation, Naydenov et al. describe a route whereby a two-step process involving the implantation of nitrogen followed by implantation of carbon atoms increases the generation efficiency of prepared, optically active NV centers by 50%. This technique should prove useful for fabricating larger-area quantum chips on which arrays of NV centers are envisaged.

    Appl. Phys. Lett. 96, 163108 (2010).

  4. Astronomy

    Too Close for Comfort?

    1. Maria Cruz

    First detected in 2008, WASP-12b is a planet with a mass 1.4 times that of Jupiter. Unlike Jupiter, though, it orbits very close to its parent star—so close that its period is only 26 hours. Thus, WASP12-b is subject to intense tidal forces and is one of the hottest and most intensely irradiated planets known. To understand the consequences of such close stellar proximity, Fossati et al. observed WASP-12b with the Cosmic Origins Spectrograph recently installed on the Hubble Space Telescope. Analysis of the near-ultraviolet part of the planet's transmission spectrum shows that WASP-12b is surrounded by an extended layer that absorbs light at the wavelengths of neutral sodium, tin, and manganese, as well as singly ionized ytterbium, scandium, manganese, aluminum, vanadium, and magnesium. This layer extends as far as 2.69 times the radius of Jupiter, well beyond the distance within which orbiting material is gravitationally bound to the planet; thus, as previously predicted, the planet is actively losing material to the star. Giant planets, like the ones in our solar system, are not expected to have elements other than hydrogen and helium in their upper atmospheres because there is little vertical mixing. To have such a metal-rich exosphere, WASP-12b must have suffered extreme mixing, possibly induced by the intense stellar irradiation and tidal effects.

    Astrophys. J. 714, L222 (2010).