This Week in Science

Science  20 Sep 1996:
Vol. 273, Issue 5282, pp. 1631
  1. Important steps

    The catalytic activity of surfaces is not uniform. Surface defects and steps are siteswith low coordination on the surface and are believed to be highly active, but the mechanisms leading to this activity are not fully understood. Zambelli et al. (p. p. 1688) studiedthe dissociation of NO on a Ru(0001) using scanning tunneling electron microscopy and identified the low-coordinated atoms at the top of atomic steps as the active sites of the reaction. Deactivation of the surface steps depended on the step geometry.

  2. Hand in the switch

    Organic materials whose structures and physical properties can be modulated by light are promising materials for reversible optical data storage and photochemicalswitches. Huck et al. (p. Organic materials whose structures and physical properties can be modulated by light are promising materials for reversible optical data storage and photochemical switches. Huck et al. (p. p. 1686 1686) present a chiroptical molecular switchthat can be operated by switching between left- and right-handed circular polarized lightof the same wavelength. The switch is based on a helical molecule that changes from one enantiomer to another upon irradiation with circular polarized light. By using the molecule as a dopant in a liquid crystalline phase, the chirality change can be expressed macroscopically.

  3. Stable cluster arrays

    A significant challenge in nanotechnology is the assembly of clusters into stable arrays. Andres et al. (p.1690 1690) present a two-step method for self-assembly of gold nanocrystals (with a mean diameter of 3.7 nanometers) into a superlattice. The clusters were synthesized with a surfactant coating (in this case an alkyl thiol) and spin castinto a film. These particles formed fragile arrays that could be stabilized by replacing the surfactant with “double-ended” dithiol or di-isonitrile organic molecules toform a linker cluster network.

  4. Fleeting subliminal cues

    How might words that appear briefly influence our judgment in the absenceof any conscious perception of having seen the word? This phenomenon of subliminal priming, in which the effect of a briefly presented word on a subsequent two-choice task is measured, has been difficult to demonstrate in an unassailable empirical fashion. Greenwaldet al. (p.p. 1699) used a response window technique to examine the performance of subjects asked to choose between unpleasant and pleasant words or between male and female names. They find that subliminal priming exists, that the influence of the prime lasts for only 100 milliseconds, and that there is no carry-over from one trial to the next. These findings are interpreted in the context of the flow of information from a sensory buffer to working memory, which leads to perception.

  5. Quality control

    When proteins misfold in the endoplasmic reticulum (ER), they are retained and degraded by a process of quality control. The site of their degradation has been unclear—degradation could occur within the lumen of the ER or elsewhere in the cell. Hiller et al. (p.p. 1725) now show that misfolded proteins in yeast are actually retro-translocated out of the ER for degradation by the cytosolic proteasome-dependent degradative system.

  6. Basic requirements

    Several cofactors are necessary in the splicing of precursor messenger RNA (pre-mRNA), a process that deletes intron sequences. One such factor is U2AF65, the 65-kilodalton subunit of U2AF, which consists of an RNA binding domain (RBD) and an arginine-serine-rich (RS) domain that promotes assembly of the U2 small nuclear ribonucleoprotein (U2 snRNP) on the upstream branch point. Valcárcel et al. (p.p. 1706) prepared RS domain mutants and found that RS function requires only a small number of basic amino acids and is not sequence specific. Other proteins were not required for the RS domain to promote base pairing between U2 snRNA and the branch point. The basic residues of the RS domain likely promote U2 snRNA binding by neutralizing the negative charge on approachingphosphates on the RNA strands.

  7. Self-splicing intron structure

    The self-splicing of RNA introns seen in Tetrahymena is catalyzed by a complex three-dimensional structure that has been understood so far in terms of modeling. In a research article and a report, Cate et al. (p.p. 1678p. 1696; seethe cover and the Perspective by Michel and Westhof, p.p.1676) present the x-ray structure of the 160-nucleotide P4-P6 domain of the Tetrahymena group I intron. A distinctive motif is the formation of pseudo-base pairs by adjacent adenosines within a helix.

  8. Brain chemistry

    The role of anandamide, a recently discovered endogenous ligand for the cannabinoid receptor, in brain function has remained elusive. Derkinderen et al. (p.p. 1719)have elucidated a signal transduction pathway after anandamide binding that could lead tochanges in the neuronal cytoskeleton and thus influence synaptic plasticity.

  9. Transport into the nucleus

    Cells must transport proteins and RNAs into and out of the nucleus continuously in order to maintain essential functions. The nucleus is surrounded by a double membrane, the nuclear envelope, which is punctuated by pores through which import and export occurs. Panté and Abei (p.p. 1729) examined the way that proteins being importedinto thenucleus interact with filaments that protrude from nuclear pores into the cytosoland howthe filaments appear to usher incoming proteins toward the pore itself.

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