This Week in Science

Science  15 Dec 1995:
Vol. 270, Issue 5243, pp. 1737
  1. Semiconductor solution

    Most semiconductors are highly covalent, nonmolecular solids, and crystals of these materials are usually grown under high-temperature conditions, either from the melt or the vapor phase. Trentler et al. (p. 1791) report a lower temperature route (at or below about 200°C) for growing crystals of III-V materials, such as gallium arsenide, from reagents in organic solvents. These crystals form as thin whiskers up to several micrometers in length.

  2. Photorefractive liquid crystals

    The index of refraction of photorefractive materials can be changed by irradiating them with laser beams in an appropriate geometry; this effect is useful in holography and optical signal processing. Twin laser beams generate electrical charges that are usually moved with an applied electric field. The charges form a refractive index grating pattern that can transfer light intensity between the beams. Wiederrecht et al. (p. 1794) doped a nematic liquid crystal mixture with both an electron acceptor and an electron donor to create a strongly photorefractive material that can operate at low applied fields and low light intensities.

  3. Aldolase antibody

    The aldol condensation couples a ketone to an aldehyde and is one of the most basic carbon-carbon bond-forming reactions in organic chemistry. Many methods exist to facilitate this reaction, but they often require stoichiometric reagents and the use of protective groups. Wagner et al. (p. 1797) have generated catalytic antibodies based on class I aldolases that can couple a wide variety of aldehydes and ketones through this reaction. These antibodies were generated by immunization with a reactive compound, a method detailed in a Research Article by Wirsching et al. (p. 1775).

  4. Supernova shock

    The OH maser line emission is thought to trace shock activity associated with supernovas. Yusef-Zadeh et al. (p. 1801; see the Perspective by Fukui, p. 1771) report the detection of this emission along the interface between the remnant of a supernova in the Milky Way (G359.1-0.5) and the surrounding ring of molecular gas. Comparison of the velocities of the molecular gas and the OH maser lines implies that the shock emissions are associated with CO material at the limb of the supernova remnant.

  5. Disease resistance in rice

    Cultivation of rice may be made easier as our understanding of the molecular basis of disease in rice improves. Song et al. (p. 1804; see the Perspective by Shimamoto, p. 1772) cloned a gene from rice, a monocot, that is responsible for resistance to a subtype of Xanthomonas oryzae. Virtually all food crop species are infected by some member of this genus of bacterial pathogens. The predicted protein product sequence is suggestive of a receptor kinase. The gene is one in a family of genes and bears a certain resemblance to the disease resistance genes recently identified in dicots.

  6. Cell fate in the eye

    In the developing compound eye of Drosophila, the protein encoded by the fat facets gene plays a role in preventing the formation of more than the required eight photoreceptor cells per eye part—mutants contain extra, ectopic photoreceptor cells. Huang et al. (p. 1842) show that the Fat facets protein is a ubiquitin-dependent protease. The protease may control the levels of a specific regulator of cell number in the eye cells during development. This result shows that a deubiquitinating enzyme can control the levels of a specific protein and that protein stability as defined by its ubiquitination state has implications in development.

  7. HIV suppressors

    Activated CD8+ lymphocytes from individuals infected with the human immunodeficiency virus secrete soluble factors that can suppress HIV infection. Cocchi et al. (p. 1811) developed a cellular assay system and have identified three chemokines, RANTES, MIP-1, and MIP-1, as the major components of the suppressive factor. Replication of HIV in infected cells could be suppressed with recombinant forms of these chemokines.

  8. Variable structure

    Antigens are recognized by T cells as peptide fragments that are bound to the T cell receptor (TCR). Fields et al. (p. 1821) have determined the structure of the variable (V) region of the TCR chain, which shows an unusual connectivity of the sheets. They used this result and the previously determined structure of the variable domain to construct a model for VV association.

  9. Chromosome order

    During prometaphase, chromosomes are briefly found in a wheel-shaped ring or rosette. Nagele et al. (p. 1831) investigated the order of the chromosomes during prometaphase and found that homologs are located across the rosette from each other. Their data also suggest that the chromosomes are grouped in two haploid sets in an antiparallel arrangement

  10. A biased response

    The nature of an immune response is governed by T helper (TH) cells. If TH1 cells dominate, cell-mediated immunity results, whereas a TH2 response can cause immunoglobulin E production, as occurs in allergic diseases. Much effort is currently focused on early events that can bias the response toward either the TH1 or TH2 type. Yoshimoto et al. (p. 1845) identified one such event. A small population of T cells, discriminated by the expression of the NK1.1 marker, produces interleukin-4 soon after antigen challenge. This cytokine helps establish conditions that favor development of a TH2 response.

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