This Week in Science

Science  21 Feb 1997:
Vol. 275, Issue 5303, pp. 1041
  1. Molecular connections in apoptosis

    Insights into the role played by molecules that interact to regulate programmed cell death, or apoptosis, are presented in four reports (see also the Perspective by Golstein, p.1081). Studies on the nematode (Caenorhabditis elegans) have shown that CED-9 (which corresponds to Bcl-2 in mammals) can protect cells from death induced by CED-3 (which corresponds to ICE, or interleukin-1beta-converting enzyme, in mammals) and CED-4, but the mechanism for this inhibition has been unclear. Chinnaiyan et al. (p.1122) show that CED-4 can simultaneously bind both CED-3 and CED-9, and Wu et al. (p.1126) show that CED-9 localized CED-4 to intracellular membranes, thus removing it from the cytosol. Another role for Bcl-2 was identified by Yang et al. (1129) and Kluck et al. (p.1132), who showed that Bcl-2 can block apoptosis by preventing the release of cytochrome c from the mitochondria.


  2. Superconductivityand symmetry

    There is still no complete model that explains why electrons form Cooper pairs in the high-temperature superconductors and cease to do so above their transition temperature. Zhang (p.1089) now presents a theory which uses rotational symmetry in five dimensions, SO(5), to relate the d-wave superconducting state to antiferromagnetism in the higher temperature insulating state. Generalized phase diagrams can be constructed with the model to relate transitions to the chemical potential (doping level) of these oxide materials. In a Perspective, Nagaosa (p.1078) discusses how this theory relates to previous models and outlines the challenges still to be met in understanding high-temperature superconductors.

  3. Copper decorations

    The scanning tunneling microscope has been used to place small copper clusters onto the surface of a gold electrode. Kolb et al. (p.1097) deposited copper electrochemically from solution onto the end of the tip. The tip is given a controlled voltage pulse that causes it to touch the surface momentarily and transfer a small cluster. Patterns and arrays can be formed by repeating the process.

  4. Five-coordinate hydrogen

    Hydrogen is usually coordinated to only one or two atoms, but in a few rare cases, coordination numbers of three and six have been observed. Bau et al. (p.1099) have synthesized a compound in which hydrogen is coordinated to five rhodium atoms in a metal cluster compound. The hydrogen atoms are located in square-pyramidal sites on the surface of the cluster. Only two of the six square pyramidal sites are occupied.

  5. Singling out molecules

    Two reports focus on single molecule measurements. Monitoring the diffusion of single molecules in free solution requires high temporal and spatial resolution. Xu and Yeung (p.1106) show that fluorescence images of a thin layer of solution recorded with an intensified charge-coupled-device camera allows continuous monitoring of single molecules at submillisecond time scales. The diffusion coefficients of the molecules could be determined from these measurements. Nie and Emory (p.1102) present a technique that provides complimentary information to the methods that are conventionally used in single-molecule studies, such as laser-induced fluorescence. Surface-induced Raman scattering of single molecules that were attached to nanoparticles showed enormous enhancements of their scattering efficiency for selected nanoparticles; the signals are more intense and stable than those obtained by fluorescence measurements.

  6. Mass survival

    The origin and early evolution of birds has been widely debated, as has the effect of the extinction at the end of the Cretaceous, which marked the demise of the dinosaurs. Cooper and Penny (p.1109) used molecular data from modern birds and estimates from the fossil record of minimum divergence times of pairs of related birds to estimate the number of modern bird lineages that survived through this extinction. Their analysis suggests that many lineages survived. Some of the implications and uncertainties related to the selection of the fossil pairs are discussed in a news story by Gibbons, p.1068.

  7. Turkey trot

    Running takes a lot of energy, but for turkeys running on level ground, contracting muscles are not doing a lot of work. Roberts et al. (p.1113; see the news story by Pennisi, p.1067) implanted fiber-length and strain gauges to measure muscle force in the large calf muscles of running wild turkeys. The stretching and recoiling of tendons and the extended muscle (which acts as a spring) do most of the work. Active contracted muscle produces the high force needed to keep the turkey standing (and thus consumes metabolic energy), but contracts only a short distance and thus produces little work.


  8. Busy terminal

    The TATA-box binding protein (TBP) is required by all three RNA polymerases. The function of its nonconserved amino-terminal end has been unknown and its conserved carboxyl-terminal end can usually substitute for the full-length protein. Mittal and Hernadez (p.1136) show that the nonconserved amino terminal mediates activity at the RNA polymerase III U6 small nuclear RNA (snRNA) promoter and recruits the snRNA activating protein complex to this site. It can also down-regulate TBP binding to the U6 TATA box and enhance U6 transcription.

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