This Week in Science

Science  18 Nov 2011:
Vol. 334, Issue 6058, pp. 875
  1. Large Ribosomal Subunit Structure


    The eukaryotic ribosome is much larger and more complex than its structurally well defined bacterial counterpart. Now, Klinge et al. (p. 941, published online 3 November) report the crystal structure of the large (60S) ribosomal subunit in complex with eukaryotic initiation factor 6 (eIF6). The structure reveals a network of interactions between eukaryotic-specific ribosomal proteins and ribosomal RNA expansion segments and uncovers the roles of eukaryotic ribosomal protein elements in the stabilization of the active site. It also elucidates the molecular basis of the interaction with elF6, which is involved in the initiation of protein synthesis and in ribosome maturation.

  2. Gorgeous Galaxies

    Galaxies grow by accreting gas from their surroundings and by converting that gas into stars. Indeed, it has long been recognized that without a source of gas replenishment, our Galaxy could not sustain its present rate of star formation. Three reports now describe data obtained by the Cosmic Origins Spectrograph and the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. Lehner and Howk (p. 955, published online 25 August) observed ionized clouds of gas traveling at high speed against a sample of 28 stars within the Milky Way, which allowed the gas cloud distances to be determined. A fraction of the clouds are inside our Galaxy and massive enough to sustain the Milky Way's present rate of star formation. As stars evolve, stellar winds and explosions expel matter from galaxies into their immediate surroundings. Tripp et al. (p. 952) probed the gas around a galaxy that has recently experienced a burst of star formation and observed an outflow of ionized gas with large mass and spatial extent. Tumlinson et al. (p. 948) examined the relationship between ionized outflows and the properties of a sample of 42 galaxies. As compared with galaxies having little or no ongoing star formation, galaxies that are still forming stars were more likely to have halos of ionized oxygen around them.

  3. Metal Veil

    A number of approaches are available for the fabrication of very-low-density materials—such as aerogels made from silica, which have remarkable strength and insulating properties. Although these materials look like frozen smoke, a 2-gram sample can support a 2.5-kilogram brick. Schaedler et al. (p. 962) devised a method to make very-low-density metallic materials based on a lattice framework. A liquid photomonomer was exposed to collimated ultraviolet light through a patterned mask to produce a 3D lattice material, which was then coated with a thin film of nickel-phosphorous. The polymer was then etched out, yielding a 3D lattice with hollow nickel-phosphorous struts.

  4. Not So Thermoset

    Synthetic polymers can be broadly divided into two categories: thermoplastics, which can be repeatedly heated or processed into different shapes, and thermosets, which are processed in the liquid state and then chemically or optically cross-linked. Once hardened, most thermoset materials are almost impossible to further process or shape. Montarnal et al. (p. 965) designed a thermoset-like material that could be processed repeatedly at elevated temperatures—and could even be ground up and recycled into a new shape while retaining the mechanical properties of the original material.

  5. Observing Ferroelectric Domain Dynamics

    Ferroelectric materials possess a spontaneous electric polarization that can be switched through the application of an electric field; this property is useful for making memory chips and radio-frequency identification tags. Nelson et al. (p. 968) studied the switching dynamics of a BiFeO3 film by using high-resolution transmission electron microscopy, and they observed localized nucleation events at the electrode-oxide interface, domain-wall pinning on point defects, and the formation of metastable ferroelectric states localized to the oxide-oxide interface.

  6. Sexual Antagonism

    Traits that are beneficial for males can be detrimental for females. For example, high testosterone and aggression may benefit males by promoting dominance, but may be detrimental in females by reducing fecundity. Thus, highly successful males can produce less successful female offspring, and vice versa. How, then, is variation in traits involved in differential fitness maintained? Mokonnen et al. (p. 972) conducted a large-scale experiment to address this question in the bank vole, a species with regular population fluctuations and a promiscuous mating system. Dominant males (with less fecund daughters) were favored in general conditions, but, when males were rare, subordinant males (and their more fecund daughters) contributed substantially to the population. A model derived from the data suggests that a combination of sexual antagonism and frequency-dependent selection can maintain genetic variation, whereas sexual antagonism alone cannot.

  7. Micromechanical Marvels


    Microelectromechanical systems, or MEMS, combine the miniaturization of both mechanical and electromechanical elements onto a single platform using the tools of microfabrication. Producing successful MEMS requires materials that are sufficiently stiff and strong, that show an electromechanical response, and that can be fabricated using compatible methods. Baek et al. (p. 958) report the epitaxial growth of a ferroelectric thin film of Pb(Mg1/3Nb2/3)O3-PbTiO3 on a Si substrate that showed a giant piezoelectric response and was used to make miniature cantilevers that could be operated using a low driving voltage.

  8. Wolbachia Finds Its Niche

    Intracellular bacteria Wolbachia are being used to help control mosquito populations in the fight against certain infectious diseases. However, relatively little is known about the cellular mechanisms responsible for Wolbachia transmission. Now, Fast et al. (p. 990, published online 20 October) describe two cellular events in the host insect that are affected by Wolbachia maternal transmission. When Drosophila mauritiana was infected with Wolbachia, mitotic activity was elevated in germline stem cells, and programmed cell death was reduced in developing egg chambers—both of which tend to increase the reproductive success of infected insects.

  9. Sickle Cell Intervention

    The damaging effects of sickle cell disease, caused by a point mutation in the gene that encodes a form of hemoglobin expressed in adults, can be lessened by reintroduction of the form of hemoglobin expressed during fetal development. Unfortunately, the fetal globin gene is usually turned off as development progresses. Using mice carrying both endogenous murine globin genes and transgenic human globin genes, Xu et al. (p. 993, published online 13 October) studied the repressor BCL11a, which silences fetal globin gene expression. Without BCL11a, expression of fetal globin persisted beyond its normal phase of development. Most patients, however, are identified after the developmental shutdown of fetal globin expression. In adult mice in which the developmental shift in globin expression had already taken place, inducible repression of BCL11a allowed a resurgence of fetal globin expression and lessened disease burden.

  10. Arrest and Tolerate


    When starving bacteria arrest their growth, they can resist killing by nearly all classes of antibiotics. Starvation is also a major cause of drug tolerance in biofilms, a bacterial community structure found in many chronic infections. Nguyen et al. (p. 982; see the Perspective by Belenky and Collins) show that such antibiotic tolerance occurs, not because the targets for antibiotics have become inactive during growth arrest, but because starvation-sensing mechanisms generate protective responses. Bacterial mutants unable to detect nutrient limitation were orders of magnitude more sensitive to antibiotic exposure, less able to establish animal infections, and failed to generate antibiotic-resistant mutants.

  11. Baby Steps

    Newborn babies can make irregular stepping motions, although it will take many months, and many falls, before those turn into walking. Even the bipedally mobile toddler does not walk like an adult. Dominici et al. (p. 997; see the Perspective by Grillner) analyzed how the patterns of human walking change with development. Walking was analyzed and categorized to be the result of a discrete set of neuromuscular components. The neonate has some of these components, which are similar to walking patterns in other mammals. The toddler has added two more components onto the basic set. And the adult has refined the components for optimal walking.

  12. When Is Less More?

    Sometimes too much information can hamper our decision-making ability, resulting in our making suboptimal choices. Freidin and Kacelnik (p. 1000; see the Perspective by Giraldeau) explored this “less is more” effect in starlings and confirmed that contextual information hampered the ability of the animals to choose the “best” food item. This was true, however, only when the birds were presented with multiple choices simultaneously. In contrast, when the birds were presented with a sequence of prey choices, knowing the context of the find improved their ability to make the optimal choice. In nature, starlings forage for invertebrates and are unlikely to encounter many prey items simultaneously. Thus, decision-making has evolved to favor using contextual information to make choices, despite the fact that it fails when choices are simultaneous.

  13. Nitrogenase Yields Its Secrets

    Nitrogenase catalyzes the reduction of dinitrogen to ammonia, which requires activating the strongest chemical bond—the triple bond of dinitrogen. The industrial process that achieves the same reaction, the Haber-Bosch process, accounts for over 1% of global energy consumption, and chemists have long sought to understand the mechanism of nitrogenase catalysis. The identity of a light atom observed in crystals of the iron molybdenum (FeMo)–cofactor at the nitrogenase active site has been unclear (see the Perspective by Ramaswamy). Spatzal et al. (p. 940) and Lancaster et al. (p. 974) used structural modeling, sophisticated spectroscopy, and computational studies to provide evidence that this interstitial ligand is most likely to be a carbon.

  14. Keeping It Quiet

    In eukaryotes, gene silencing is essential for regulating cell fate. A well-studied example is the silent information regulator (SIR) complex that regulates mating type in yeast. Armache et al. (p. 977) present a crystal structure of a domain of a key protein in the complex, Sir3, bound to a nucleosome core. The extensive molecular contacts observed explain how known mutations in Sir3 and histones affect silencing and how covalent modification of two histones regulates Sir3 binding to the nucleosome. Features of the crystal packing provide hints as to how the observed Sir3 nucleosome interface might be integrated into a larger structure to compact and silence long regions of chromatin.

  15. Bacterial Protection

    Most bacteria are capable of producing hydrogen sulfide and use a trio of enzymes to do so. Classically, this gas was considered a by-product of sulfur metabolism, but knowing that nitric oxide protects Gram-positive bacteria against oxidative stress, Shatalin et al. (p. 986; see the Perspective by Belenky and Collins) discovered that H2S probably does likewise. When the H2S-producing enzymes were inactivated, bacteria became more susceptible to antibiotics unless supplied with a source of H2S.

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