This Week in Science

Science  13 Oct 1995:
Vol. 270, Issue 5234, pp. 213
  1. Binding of homeodomain heterodimers to DNA

    The MAT alpha-2 homeodomain protein of yeast regulates transcription by binding DNA with either MAT alpha-1 or MCM1. Each of the complexes, a1/alpha-2 and alpha-2/MCM1 bind to distinct sites in the yeast genome and repress transcription of the adjacent genes in a cell type-specific manner. Li et al. (p. 262; see the Perspective by Andrews and Donoviel, p. 251 ) present the crystal structure of the a1/alpha-2 heterodimer bound to DNA. The alpha-2 COOH-terminal tail is disordered when alpha-2 binds DNA alone but becomes ordered in the ternary complex and contacts the a1 homeodomain. Such flexible protein recognition domains may mediate contact between many other heterodimeric transcription factors. Jin et al. (p. 209) examine the requirements for proper spacing between the a1/alpha-2 DNA binding sites and the length of the alpha-2 tail.

  2. Quantum computation

    One approach for making smaller integrated circuits would be a quantum computer in which the logic states 0 and 1 would be replaced by wave functions and the logic operations by superpositions of quantum states. Theory suggests that quantum computers could be very powerful for tasks such as in Shor's factorization of prime numbers. In a review, DiVincenzo (p. 255) notes that a working quantum computer would be extremely demanding and would require a huge extension of the rudimentary quantum computing possible today

  3. Magnetoresistive materials

    In seeking new materials, combinatorial libraries can be used to synthesize and screen a large number of samples rapidly. Briceño et al. (p. 273) used this method to search for materials that exhibit strong magnetoresistance, a property of great interest for downsizing magnetic recording heads. They found a class of cobalt oxides that have large magnetoresistance, and further determined that in contrast to manganese-based compounds, the effect increases as the material is doped with larger alkaline earth ions.

  4. Lifting mountains

    What forces cause the uplift of large mountain ranges? Small and Anderson (p. 277 ; see cover) examine the interplay of erosion and generation of relief, which removes load and induces isostatic uplift, on the formation of the Sierra Nevada, California. Their model shows that coupled erosion along the crest of the range and deposition in the Great Valley could have produced the observed tilting of the range to the west and apparent uplift on the east. Summit elevations may have increased while the mean elevation of the range may have decreased in the past 10 million years.

  5. Rock vein pursuit

    Pseudotachylites are veins or larger bodies of melted rock formed by frictional melting, most commonly during asteroid impacts or faulting. The conditions responsible for their formation have been obscure because analogous features have been difficult to produce in the lab. Fiske et al. (p. 281) generated pseudotachylites in high-velocity shock experiments in which they used an aluminum container that deformed with the sample, facilitating strain heating. Strain heating may thus complement shock heating in melting and altering rocks in impact events.

  6. Glucocorticoid mechanism

    Although they have been used for years as immunosuppressive and anti-inflammatory agents, little is known about the mechanism of glucocorticoid (GC) action. Scheinman et al. (p. 283) and Auphan et al. (p. 286; see news story by Marx, p. 232) show that the nuclear factor kappa B (NF-kappa B) transcription factor, a regulator of genes involved in the immune response, is repressed by GCs, and that GCs induce increased synthesis of I kappa B alpha, the inhibitor of NF-kappa B. This additional I kappa B alpha binds to NF-kappa B, preventing its action.

  7. Hearty protein

    How large is large? For proteins, most lie within the range of 180 to 900 amino acid residues per molecule (masses of 20,000 to 100,000 daltons). Labeit and Kolmerer (p. 293 ; see the news story by Barinaga,p. 236) present the molecular .htmlcloning and sequencing of titin, a protein from human heart of 26,926 residues (3 million daltons). Analysis of the sequence domains, the messenger RNA splicing patterns in various tissues, and the structural organization of other muscle proteins suggests that titin serves two functions. First, it specifies the global arrangement of thick, mysoin-containing filaments in muscle and, second, selective expression of domains explains the different elasticity of muscles

  8. Peroxide pathway

    Binding of platelet-derived growth factor (PDGF) to its receptor initiates a number of events that transmit signals within the cell. Sundaresan et al. ( p. 296 ) report that treatment of vascular smooth m.htmluscle cells with PDGF increases the intracellular concentration of hydrogen peroxide (H2O2). Responses of the cells to PDGF, such as enhanced DNA synthesis and chemotaxis, were inhibited when the this increase in H2O2 was blocked. Thus H2O2, like nitric oxide, may function in signal transduction.

  9. Parts of speech

    Speech conveys information through both the frequency distribution of sounds (spectral information) as well as timing for making different sounds (temporal cues). Shannon et al. (p. 303) show that speech can be recognized with high accuracy even if the spectral information is highly degraded. They added white noise to spoken words and sounds in a way that preserved temporal cues but reduced frequency information into only a few broad bands. Vowels and consonants could be recognized with only three bands of modulated noise. Such results bear not only on how speech is processed in the human brain but can also be useful in designing hearing aids.

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