This Week in Science

Science  24 May 2002:
Vol. 296, Issue 5572, pp. 1361
  1. In Brevia

    Critical differences in speech that occur when people talk to pets rather than to babies are described by Burnham et al. (p. 1435).

  2. Multitasking Molecules

    An organic molecular conductor based on a spiro-biphenalenyl neutral radical can simultaneously exhibit bistable electrical, optical, and magnetic states that arise through internal charge transfer. Itkis et al. (p. 1443) show that in the high-temperature paramagnetic form, the unpaired electrons are separated on the exterior phenalenyl units of a dimer unit. In the spin-paired low-temperature diamagnetic state, the electrons migrate to the interior phenalenyl units and spin pair as π-dimer. The paramagnetic state is electrically insulating and transparent in the infrared, whereas the diamagnetic state is conducting and opaque in the infrared.

  3. Traces of Monkey Business

    To what degree do chimpanzees use tools, and how might their use look in an archaeological context? Mercader et al. (p. 1452; see the news story by Vogel) describe an excavation of a chimpanzee nut-cracking site, in which chimpanzees evidently collected useful stones and transported them to the site. The site shows a large number of flaked and broken stones that may superficially resemble aspects of early hominid sites.

  4. Cyclic Universe

    The standard model of the origin of the universe begins with the big bang, which was followed by a period of inflation, a brief period of rapid expansion of spacetime. Steinhardt and Turok (p. 1436) have revived an old theory by proposing a new model that has no beginning or end, but is composed of a series of bangs (explosive expansions) and crunches (contractions). They use a negative potential energy, which is motivated by string theory, rather than spatial curvature to cause the reversals from expansion to contraction. Unlike the standard model, the cyclic universe can explain the recent discoveries of accelerated expansion and dark energy.

  5. The Great Escape

    The hypothesis that human immunodeficiency virus-type 1 (HIV-1) mutates in order to “escape” recognition by cytotoxic T cells (CTL) has endured for over a decade without direct evidence to support it. Moore et al. (p. 1439; see the Perspective by McMichael and Klenerman) searched at a population level for selection of HIV-1 variants within a sequence corresponding to 207 amino acids of the viral reverse transcriptase gene. In an extensive cohort of HLA allele-typed individuals, polymorphisms in or around CTL epitopes covered by the consensus sequence were significantly associated with high viral load. Evasion of HIV-1 from the CTL radar screen will be a critical consideration in HIV-1 vaccine and therapy design.

  6. Unpredictable Wiring Diagrams

    Making predictions of the behavior of genetic networks may be even more complicatd than previously thought. Guet et al. (p. 1466; see the Perspective by Wigler and Mishra) created libraries of synthetic genetic networks in Escherichia coli. LacI, TetR, and lambda CI, along with five promoters regulated by these proteins, were linked together in various orders on plasmids. Two chemical inducers that change the binding state of LacI and TetR were used as inputs, and a fluorescent reporter of activity was used as the output. There were surprises even within such well-characterized components. A single swap of the connections between promoter and DNA binding protein could dramatically change the behavior of the network.

  7. Signaling Shortcut

    The yeast mating response to pheromones involves transmission of signals through a cascade that begins at a cell surface pheromone receptor, couples to a heterotrimeric GTP-binding protein (G protein), and eventually activates a mitogen-activated protein kinase (MAPK). Metodiev et al. (p. 1483) report that the subsequent adaptation response to pheromones relies on this same general pathway but uses a shortcut. The Gα subunit of the G protein interacts directly with the downstream MAPK to down-regulate the mating signal. This strategy of circumvention may be applicable to other G protein-stimulated MAPK cascades in higher eukaryotes.

  8. Life Signs Lost in Igneous Rocks

    Pinpointing when life began on Earth has been difficult. The oldest fossils have been thought to be in rocks dated to 3.45 billion years ago, but recent results have questioned the biological origin of the purported fossils. Chemical evidence for older life has been presented based on carbon isotope signatures in ancient rocks in Greenland. The oldest signature has been reported to be preserved in graphite inclusions in apatite crystals in metamorphic rocks on the Island of Akilia thought to be 3.8 billion years old. These graphite inclusions were interpreted as representing organic matter deposited with the rocks, which were thought to be sedimentary iron formations. Fedo and Whitehouse (p. 1448; see the news story by Kerr) now argue that the host rocks are actually igneous rocks that were subsequently altered to form prominent banding. Any organic matter would not be primary in origin.

  9. Preparing to Make the Cut

    The hairpin ribozyme cleaves its substrate with heterogenous reaction kinetics. Now Zhuang et al (p. 1473) have used single-molecule fluorescence methods to show that this heterogeneity in function is linked to complex structural dynamics. The ribozyme exists either in an undocked conformation or in one of four distinct docked states. Individual molecules exhibit a “memory effect” and rarely switch between different docked states. Cleavage only occurs in the docked state, and the combination of multiple undocking rates and the memory effect explains the heterogenous cleavage reaction kinetics. Complex structural dynamics linked to function is likely a general feature of RNA kinetics.

  10. Learning in Adults and Children

    One of the challenges in studying the development of cognitive functions in humans is the expectation that both anatomical and functional components of the brain are developing, not merely during infancy but well into adolescence and perhaps even adulthood. Schlaggar et al. (p. 1476; see the Perspective by Casey) provide a behavioral and brain imaging study in which they describe a new approach for parsing age-related and performance-related developmental events. They assess how children (ages 7 to 10) and adults generate words in a lexical processing task, and they find that adults utilize a left dorsal frontal region, while children apparently do not have functional access to this region and rely on an extrastriate area. One explanation is that this alternative strategy is discarded as frontal functions mature.

  11. Whither Thou Goest...

    In addition to the generation of movements, the brain must also create an internal record providing information about impending movements. Information about upcoming movements is generated by creating a correlate, or corollary discharge, of the neuronal activity that commands movement. Sommer and Wurtz (p. 1480) provide evidence for correlate formation in the case in a previously identified pathway from brainstem to frontal lobe. Corollary discharge signals emanating from the superior colliculus are relayed through the mediodorsal nucleus of the thalamus upstream toward the frontal eye field. The prefrontal areas will be informed through this pathway of collicular neuronal activity associated with the generation of ocular saccades.

  12. A New Order

    Almost a century has elapsed since a newly described insect has proved unplaceable within a recognized order—major groupings, such as beetles and flies. Now, Klass et al. (p. 1456: see the 19 April news story by Pennisi) announce the discovery of a new extant insect taxon: The new order, Mantophasmatodea, appears to be related to Phasmatodea (stick insects), and is described on the basis of two museum specimens from Namibia and Tanzania. The authors also note the occurrence of Mantophasmatodea in Baltic amber, which demonstrates a much wider geographical distribution of the group in the Tertiary.

  13. Adding Pyrrolysine to the Code Book

    In 1986, selenocysteine was identified as the 21st amino acid when it was found to be directly encoded by UGA, which usually specifies translation termination. Now two reports show that amber codons in the methyltransferase genes of certain archaea encode a novel lysine derivative (see the Perspective by Atkins and Gesteland). Hao et al. (p. 1462) provide crystallographic evidence that UAG is decoded as pyrrolysine, and Srinivasan et al. (p. 1459) characterize a specialized transfer RNA (tRNA) that can be charged with lysine by an unusual tRNA synthetase. By analogy with the selenocysteine translation mechanism, it is likely that the tRNA is charged with lysine and is then modified to pyrrolysine before UAG is decoded.

  14. A Clue to Cachexia

    Patients with chronic diseases such as cancer and AIDS often develop cachexia, a life-threatening disorder characterized by extensive weight loss and degeneration of skeletal muscle. The molecular pathogenesis of cachexia is poorly understood. Zimmers et al. (p. 1486) show that mice develop a wasting syndrome resembling human cachexia when they are systemically administered high levels of myostatin, a member of the transforming growth factor-β family. Prior administration of proteins that inhibit myostatin activity, such as follistatin, slowed weight loss in the mice. These results suggest that myostatin may be a useful drug target for prevention or treatment of cachexia, which is estimated to be the ultimate cause of death in about 25% of all cancer patients.

  15. Asteroidal Partners in Crime

    The probability that a near-Earth object will impact our planet is usually low, but the potential for damage is so high that searches and characterization of this population of objects are still important. Margot et al. (p. 1445) have detected several binary asteroid systems in radar images in the near-Earth environment and calculate that 16% of the population (with diameters greater than 200 meters) is composed of binaries. Other binaries may have been the culprits for some dual impact craters, such as the Ries-Steinheim crater system in Germany. In addition, the mechanism of formation of these binaries, possibly by tidal disruption during a close pass by a planet, can provide a better understanding of the origin and evolution of the solar system.

  16. Plant Peptide Receptor

    Many small peptides that serve as important signaling molecules have been identified in animals, and more recently, similar molecules have been recognized in plants. Matsubayashi et al. (p. 1470) have now identified the likely receptor for a sulfated peptide, phytosulfokine, in carrot cells. The protein is a receptor kinase with a single transmembrane domain and features leucine-rich repeats in the extracellular domain. Interactions between the phytosulfokine and its receptor regulate proliferative and regenerative ability of the plant tissues.

  17. Calculating Forest Biomass Changes in China

    Fang et al. (Reports, 22 June 2001, p. 2320), using historical forest inventory records, calculated that forest biomass storage of carbon in China had increased significantly since the mid-1970s, “mainly due to forest expansion and regrowth.” Zhang and Xu comment that “the equation used to estimate forest biomass” by Zhang et al. “is questionable,” because it purportedly relies on site classification data that “have not been available in any Forest Resource Statistics of China since the 1950s.” Fang et al., in their response, show that the expression cited in the original paper is “mathematically equivalent” to a simpler expression that does not depend on site class information. The full text of these comments can be seen at