This Week in Science

Science  02 Nov 2012:
Vol. 338, Issue 6107, pp. 578
  1. Ocean Monarchs

    CREDIT: JOHN R. TAYLOR AND ROMAN STOCKER

    It is hard to grasp that the unseen microorganisms of the oceans are the most productive on the planet, at orders of magnitude greater than sharks and whales or even terrestrial forests. The plankton is thus a major contributor to the geochemical cycles that are currently under pressure from climate change. Stocker (p. 628) reviews the state of knowledge of the web of myriad ephemeral microenvironments within the ocean's bulk and how microorganisms respond to the ever-shifting chemical spectrum. To this end, Taylor and Stocker (p. 675) report experiments on the effects of turbulence on nutrient uptake by chemotactic marine bacteria. They propose that turbulence favors motile bacteria that adopt an optimal foraging strategy, which trades off the relative high cost of motility to gain the benefits of plumes of nutrients by zipping between them at optimized speeds. Scaled up, such apparently “micro” behavior will influence the rate of remineralization of dissolved organic matter and in turn will feed into global patterns of geochemical cycling.

  2. Twist and Entangle

    Entanglement is a key feature in quantum information science and plays an important role in various applications of quantum mechanics. Fickler et al. (p. 640) present a method for converting the polarization state of photons into information encoded into spatial modes of a single photon. From this, superposition states and entangled photons with very high orbital angular momentum quantum numbers were generated.

  3. Push Me, Release, Pull You

    In eukaryotic cells, nearly all long-distance transport of cargos is carried out by the microtubule-based motors kinesin and dynein. These opposite-polarity motors move cargos bidirectionally so that they reach their cellular destinations with spatial and temporal specificity. To understand transport by motor ensembles, Derr et al. (p. 662, published online 11 October; see the Persective by Diehl) used a DNA scaffold for building an artificial cargo that could be programmed to bind different numbers and types of molecular motors with defined geometry. A cargo with multiple copies of the same motor was transported with minimal interference, suggesting that similar-polarity motors can coordinate without the need for additional cellular factors. However, ensembles of opposite-polarity motors frequently engaged in a sort of “tug of war,” which could only be resolved by releasing one motor from the microtubule track. Thus, within the cell, it is likely that regulation is required for bidirectional transport.

  4. Dating the First Solids

    The solar system's first solids: calcium-aluminum–rich inclusions and chondrules are found in meteorites and provide a direct record of the dynamics of the solar protoplanetary disk that led to the formation of the solar system. Previous results indicate that chondrules formed 1 to 2 million years after the inclusions—an age difference that has been used in constructing models of chondrule formation. Based on uranium- and lead-isotope measurements of a collection of these primitive materials, Connelly et al. (p. 651) show that chondrules in fact started to form at the same time as the inclusions, 4.567 billion years ago, and that their formation took about 3 million years.

  5. PolII Goes Loopy

    To execute their function, genes must be transcribed into RNA, often by RNA polymerase II (PolII), which binds at the 5′ end of genes and therefore transcribes through the coding region to make messenger RNA. But, presented with nucleosome-depleted chromatin, PolII will, wastefully, initiate transcription nonspecifically and bidirectionally away from the gene. Noting that actively transcribed genes often form loops, such that their 5′ and 3′ ends are juxtaposed. Tan-Wong et al. (p. 671, published online 27 September; see the Perspective by Hampsey) showed that PolII's propensity for promiscuous bidirectional transcription is reined in by gene loop formation.

  6. Delaying Quantum Choice

    CREDIT: UNIVERSITY OF BRISTOL

    Photons can display wavelike or particle-like behavior, depending on the experimental technique used to measure them. Understanding this duality lies at the heart of quantum mechanics. In two reports, Peruzzo et al. (p. 634) and Kaiser et al. (p. 637; see the Perspective on both papers by Lloyd) perform an entangled version of John Wheeler's delayed-choice gedanken experiment, in which the choice of detection can be changed after a photon passes through a double-slit to avoid the measurement process affecting the state of the photon. The original proposal allowed the wave and particle nature of light to be interchanged after the light had entered the interferometer. By contrast in this study, entanglement allowed the wave and particle nature to be interchanged after the light was detected and revealed the quantum nature of the photon, for example, it displays wave- and particle-like behavior simultaneously.

  7. Perovskite Photovoltaics

    For many types of low-cost solar cells, including those using dye-sensitized titania, performance is limited by low open-circuit voltages. Lee et al. (p. 643, published online 4 October; see the Perspective by Norris and Aydil) have developed a solid-state cell in which structured films of titania or alumina nanoparticles are solution coated with a lead-halide perovskite layer that acts as the absorber and n-type photoactive layer. These particles are coated with a spirobifluorene organic-hole conductor in a solar cell with transparent oxide and metal contacts. For the alumina particles, power conversion efficiencies of up to 10.9% were obtained.

  8. Chloroplast Rescued by Ubiquitin

    The ubiquitin proteasome system is important in the regulation of many nucleocytosolic processes. However, its regulatory reach was not thought to extend to the chloroplast. Using a forward-genetic screen in Arabidopsis, Ling et al. (p. 655; see the Perspective by Kessler) identified a ubiquitin E3 ligase, termed SP1, embedded in the chloroplast outer envelope membrane. SP1 was found to target components of the chloroplast protein import machinery for degradation by the ubiquitin proteasome and was important for changes in chloroplast biogenesis.

  9. Necrophilic Bandit Fungi

    CREDIT: LORANG ET AL.

    The immune systems that plants use to defend against pathogens normally deflect attack. However, Lorang et al. (p. 659, published online 18 October) have identified a rearguard susceptibility that a necrotrophic fungus exploits. The fungal toxin victorin interacts with the defense protein LOV1 in Arabidopsis and activates it, but the result, counterintuitively, is that the plant succumbs to the disease rather than fighting it off. What seems to be happening is that victorin targets a thioredoxin that regulates the systemic acquired resistance pathway. That interaction triggers activity of LOV1, which in turn incites cell death. The invading fungus then benefits from the ready access to dead cells.

  10. Epigenetic Inheritance

    A long-standing question is whether and how stem cells maintain their epigenetic information. Knowing that many types of stem cells undergo asymmetric cell divisions, Tran et al. (p. 679) probed the asymmetric division of Drosophila male germline stem cells and found that preexisting histones were selectively segregated to the stem cell, whereas new histones were enriched in the daughter cell that underwent differentiation. By contrast, asymmetric histone distribution was not seen in progenitor cells. This study suggests that stem cells retain preexisting canonical histones during asymmetric cell divisions in vivo.

  11. Poor Choices

    Two categories of reasons for why poor people make economically unsound choices, such as obtaining a payday loan at an extraordinarily high rate of interest, reflect, first, the environment: Poor people are more likely to be living in poor neighborhoods with higher rates of crime and lower rates of social services. Second, they reflect the individual: People are poor in part because of their own psychological dispositions toward impatience and impulsiveness. For both cases, obtaining causal evidence in controlled experiments has been challenging. Shah et al. (p. 682; see the Perpective by Zwane) propose a third category of reasons whereby being poor exerts a bias on cognitive processes and provide evidence for it in laboratory experiments performed in scenarios of scarcity.

  12. Ullman Upgrade

    Precious metals may dominate contemporary catalysis, but the early development of synthetic organic chemistry relied on more abundant elements—a strategy that chemists are returning to now for the sake of sustainability. Copper-mediated coupling of aryl halides with amines was reported by Ullman more than a century ago and remains in use today for the synthesis of certain organic compounds. However, the reaction generally requires high temperature to proceed efficiently. Creutz et al. (p. 647) have developed a photochemical variant that uses copper and reacts at room temperature or below, apparently by a radical mechanism.

  13. Symportin Synchrony

    Ribosomes, the macromolecular machines responsible for protein synthesis, function in the cytoplasm but are assembled in the nucleus. Ribosomal proteins must be imported into the nucleus, but how this is coordinated with assembly is unclear. Kressler et al. (p. 666) report that two 5S rRNA binding proteins are coimported into the nucleus. They identify a transport adaptor, which they term symportin (Syo1), that binds simultaneously to Rpl5 and Rpl11. Syo1 also interacts with the import receptor Kap104, which facilitates import of the Syo1-Rpl5-Rpl11 complex. Synchronous nuclear transport may be more generally used to coordinate assembly processes.

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