Editors' Choice

Science  09 Jan 2004:
Vol. 303, Issue 5655, pp. 146

    A Red-Shifted Beetle

    1. Andrew M. Sugden

    Evolution is a process that manifests itself at every level of biological organization, from molecule to population. However, it is rare that it can be observed and measured at all these levels simultaneously to provide an unbroken chain of cause and effect. Stolz et al. have made such a connection of natural selection for bioluminescence in the Jamaican click beetle, Pyrophorus plagiophthalamus, which is unique among light-producing organisms in having a color polymorphism: yellow-green to orange in the ventral light organs, and green to yellow-green in the dorsal organs. The variation results from individual amino acid substitutions in luciferase, the enzyme involved in the light-generating reaction, which in turn can be traced to individual nucleotide substitutions in luciferase genes. A phylogenetic analysis shows that there has been a series of such substitutions, producing an adaptive trend toward orange ventral organs in P. plagiophthalamus in Jamaica. The final step to complete this picture will be to identify the selective agent; likely candidates are sexual selection or preferential predation on beetles with yellow ventral organs. — AMS

    Proc. Natl. Acad. Sci. U.S.A. 100, 14955 (2003).


    A Fistful of Factors

    1. Gilbert J. Chin

    One of the familiar leitmotifs of biological regulation is a cascade of switches aimed at a crucial go-no go control point. The initiation of protein synthesis is one such point, and assembly of the translational machine, the ribosome, on the messenger RNA (mRNA) is a carefully thought-out decision.

    In the developing Drosophila oocyte, oskar mRNA is donated by the surrounding nurse cells, and posterior patterning of the oocyte requires spatially restricted translation of oskar mRNA. Wilhelm et al. show that the protein Cup binds to eukaryotic initiation factor 4E (eIF4E), which sits at the capped 5' end of the mRNA. Cup acts to recruit oskar mRNA to the posterior region and to keep it translationally inactive until it gets there. Nelson et al. show that the Oskar protein appears to exercise a similar regulatory oversight of nanos mRNA, whose translation is inhibited by the interaction between Smaug and Cup, which is in contact with eIF4E bound at the 5' end of the nanos mRNA. Oskar binds to Smaug, and this may result in disruption of the Cup-eIF4E interaction.

    Why is it so crucial to control access to eIF4E? Gross et al. describe the structure of the complex between eIF4E and eIF4G. The 4G factor is itself part of a multiprotein complex that serves as a platform for integrating kinase-communicated signals and the subsequent steps of small and large ribosome subunit assembly. The contact between these two factors encompasses a large surface area formed by threading the bracelet-like eIF4G onto the initially unfolded N-terminal α-helix of eIF4E, which then organizes into a fist-like domain, locking eIF4G into place. — GJC

    J. Cell Biol. 163, 1197 (2003); EMBO J. 10.1038/sj.emboj.7600026 (2003); Cell 115, 739 (2003)


    High and Dry

    1. H. Jesse Smith

    Venice is being swallowed by the sea. The combination of land subsidence due to groundwater pumping and sea level rise due to global warming has increased the water level in the city by 23 cm in the past 100 years, and a further rise of about 50 cm is projected to occur over the next century. The frequency of the floods known as “acqua alta” has increased; these events submerge large areas of the city by as much as a meter in extreme cases. Various measures have been proposed to safeguard the islands from the high waters, such as the construction of a set of movable gates across the three entrances to the lagoon in which Venice resides, but none have convinced all of the critics.

    In a departure from the idea that the solution is to control the sea, Comerlati et al. offer a fundamentally different proposal: raise Venice by pumping CO2 or seawater into the brackish aquifer that lies 600 to 800 m beneath the city. They estimate that the city could be raised by as much as 30 cm in 10 years if seawater were used, and up to 24 cm if CO2 were used, which would have the added benefit of reducing Italy's net greenhouse gas emissions. This strategy could avoid the potentially harmful side effects that repeatedly restricting water flow into the lagoon would precipitate and could eliminate all but the severest of the acqua alta episodes, which would make raising the gates an infrequent necessity. — HJS

    Eos 84, 546 (2003).


    Copper Stopper

    1. Ian S. Osborne

    As the trend to shrink the feature size of integrated electronic devices continues, and circuit design becomes more three-dimensional, there is also an accompanying practical issue to address, which relates to maintaining the compatibility of the mechanical and electrical isolation layers and materials. The role of such barrier layers is vital in preventing the electrical lines from shorting and the devices from failing due to copper diffusing into the active region of the devices. For future device fabrication sizes of 45 nm, it is expected that the present barrier technology based on TaN will not be effective and that a new approach will be required. Mikami et al. have investigated self-assembled monolayers (SAMs) for this purpose. They fabricated simple capacitive devices and looked at their lifetime under the thermal and electrical stresses of typical operating conditions. Their results show that a SAM layer just 1.7 nm thick is a sufficient barrier to copper diffusion and that the estimated lifetime of such a barrier layer should be in excess of 10 years. — ISO

    Appl. Phys. Lett. 83, 5181 (2003).


    Taking Hold of Iron Oxidation

    1. Phil D. Szuromi

    Both heme and nonheme iron enzymes can oxidize C-H bonds. For the oxidation of such bonds in cyclohexane, it is believed that an Fe(IV)=O species affects this transformation. It has been unclear whether a similar one-electron-reduced species in a non-heme ligand environment would be able to oxidize stronger C-H bonds. Previous studies have shown that Fe(IV) complexes stabilized with tetradentate N4 ligands could perform atom transfer reactions; for example, the tripodal ligand tris(2-pyridylmethyl)amine can epoxidize the double bond of cyclooctene. Kaizer et al. show that two different pentadentate N5 ligands form Fe(IV)=O complexes that are able to hydroxylate the C-H bonds in cyclohexane and are stable enough to perform this reaction at room temperature. These findings support mechanisms that invoke the Fe(IV)=O intermediates in mononuclear nonheme iron enzymes. — PDS

    J. Am. Chem. Soc. 10.1021/ja037288n (2003).


    Finding the Way Back

    1. Stella M. Hurtley

    After injury to a nerve, specific proteins of the axon are transported back into the cell body in order to promote repair and regrowth processes. Hanz et al. find that axoplasmic proteins bear nuclear localization signals (NLSs) and that, after nerve injury, the levels of the NLS-binding protein importin β increase because of local translation of axonal mRNA. Complexes between the axoplasmic NLS-bearing proteins and importin then form, and these are transported in a retrograde fashion by the motor protein dynein. If the NLS-protein-importin interaction is blocked by the addition of exogenous NLS peptide, regenerative outgrowth from the cell body is inhibited or delayed. Thus, lesion-induced up-regulation of importin β in the axon is important in promoting nerve regeneration. — SMH

    Neuron 40, 1095 (2003).

  7. STKE

    A ChIP off the Transcription Clock

    1. Nancy Gough

    Regulation of gene expression involves the recruitment to and assembly of multiprotein complexes on DNA. Métivier et al. used the promoter region of the pS2 gene to study how the human estrogen receptor stimulates transcription of this gene. Using chromatin immunoprecipitation (ChIP) analysis, they found more than 30 proteins that bind to the promoter in the presence of estrogen; however, many of these interactions were mutually exclusive. The complexes formed could be grouped into six different classes. Kinetic ChIP analysis revealed the order of complex assembly, and histone modifications were also monitored. Their analysis identified three types of cycles of ordered complex assembly and disassembly and chromatin modification, which they present in a model for the formation of one transcriptionally silent cycle followed by two distinct transcriptionally active cycles. — NG

    Cell 115, 751 (2003).

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