Articles Alert

The Scientist has asked a group of experts to comment periodically upon recent articles that they have found noteworthy. Their selections, presented herein every issue, are neither endorsements of content nor the result of systematic searching. Rather, the list represents personal choices of articles the columnists believe the scientific community as a whole may also find interesting. Reprints of any articles cited here may be ordered through The Genuine Article, 3501 Market St., Philadelphia, Pa. 19104, or by telephoning (215) 386-4399. Author: SIMON SILVER Department of Microbiology & Immunology University of Illinois Chicago Telomeres "tell" chromosomes where to end and prevent loss of chromosome tips. They may also be involved in chromosomal association during mitosis and meiosis. The formation dimers of telomere hairpin structures have been demonstrated through the use of synthetic telomere DNA oligonucleotides in vitro. The synthetic structure used consists of four guanine residues, hydrogen-bonded in a circular array, and four tetra-guanine structures stacked, making a cage consisting of 16 residues. This development has the potential to explain many in vivo properties of telomeres. W.I. Sundquist, A. Klug, "Telomeric DNA dimerizes by formation of guanine tetrads between hairpin loops," Nature, 342, 825-9, 14 December 1989. (Medical Research Council Laboratory of Molecular Biology, Cambridge, England) Nuclear membranes have large pores, some as much as 9 nanometers across. Through these channels, there are specific transport mechanisms for the movement of mRNA and preribosomes outward, and nuclear proteins inward. In vitro reconstitution experiments with Xenopus and rat nuclear fractions define the role of a 62-kilodalton membrane glycoprotein in the ATP-dependent uptake of a protein with a TRITC (tetramethyl rhodamine isothiocyanate) signal peptide. D.R. Finlay, D.J. Forbes, "Reconstitution of biochemically altered nuclear pores: Transport can be eliminated and restored," Cell, 60, 17-29, 12 January 1990. (University of California at San Diego, La Jolla) Although Nobel Prize lectures don't usually appear in print for a year or so, Science has already published one of this year's four awards for molecular biology. New work on catalytic RNA molecules, functioning as RNAses, shows that residue C92 of the RNA component of RNAse P is required for recognition of the correct cutting position in a tRNA precursor substrate. C. Guerrier-Takada, N. Lumelsky, S. Altman, "Specific interactions in RNA enzyme-substrate complexes," Science, 246, 1578-84, 22 December 1989. (Yale University, New Haven, Conn.) Bacterial tryptophan synthase consists of two subunits that function as a tetramer, àá2à, and carry out two sequential reactions in tryptophan synthesis. The protein contains an intraprotein "tunnel" that channels indole (the product of the first enzymatic reaction) from the active site in the à subunit to the site of tryptophan synthesis from indole in the á subunit. C.C. Hyde, E.W. Miles, "The tryptophan synthase multienzyme complex: exploring structure-function relationships with X-ray crystallography and mutagenesis," Bio/Technology, 8, 27-32, January 1990. (National Institutes of Health, Bethesda, Md.) The American Society of Biochemistry and Molecular Biology has compiled the 35 "minireviews" that appeared in the 1989 issues of the Journal of Biological Chemistry and presented the collection to members of the society. These reviews cover most of the hot topics in biochemistry and molecular biology, and are especially recommended for teaching. Journal of Biological Chemistry, The American Society for Biochemistry and Molecular Biology Inc., Baltimore, 1990. Author: PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. The characterizations of lead isotopes at the Cretaceous-Tertiary (K/T) boundary (as observed in a deep-sea core) do not match those of the Deccan Traps of India, the supposed source of volcanism in the volcanism hypothesis of K/T extinction. Nor do they match those of stony meteorites, possibly implicated in the impact hypothesis. However, the data do not preclude an impact by an iron meteorite. J.G. Galer, J.D. Macdougall, D.J. Erickson III, "Pb isotopic tracers of the Cretaceous-Tertiary extinction event," Geophysical Research Letters, 16, 1301-4, November 1989. (Scripps Institution of Oceanography, La Jolla, Calif.) Examination of continental shelf sections in Texas and Tunisia shows that extinctions of planktonic foraminiferal species extend for hundreds of thousands of years above and below the K/T boundary. This shows no consistency with either the impact or the volcanism hypothesis of extinction. It perhaps points to multiple, unrelated causes, including sea-level regression and global cooling as well as impact and volcanism. G. Keller, "Extended period of extinctions across the Cretaceous/Tertiary boundary in planktonic foraminifera of continental-shelf sections: implications for impact and volcanism theories," Geological Society of America Bulletin, 101, 1408-19, November 1989. (Princeton University, N.J.) Laboratory experiments show that some common bacteria and fungi can enhance, erase, and disperse sedimentary iridium anomalies, and can even create them from terrestrial sources of iridium. This may or may not invalidate the interpolation of the K/T iridium anomaly in terms of a bolide impact, but it throws doubt on estimates of bolide size and the scale of the impact. B.D. Dyer, N.N. Lyalikova, D. Murray, M. Doyle, et al., "Role for microorganisms in the formation of iridium anomalies," Geology, 17, 1036-9, November 1989. (Wheaton College, Norton, Mass.; Institute of Microbiology, Moscow; University of Rhode Island, Kingston; et al.) Ion-microprobe uranium-lead analysis of zircons shows that the Acasta gneisses of the western Slave province, Canada, are the oldest intact terrestrial rocks yet identified, at 3,962 ñ 3 million years old. Examples of the rock from which the gneisses were derived may still be present in the Slave province. S.A. Bowring, I.S. Williams, W. Compston, "3.96 Ga gneisses from the Slave province, Northwest Territories, Canada," Geology, 17, 971-5, November 1989. (Washington University, St. Louis; Australian National University, Canberra) The hypothesis that flood-basalt provinces occur above hot mantle plumes that produce uplift (doming) of the continent receives support from a study of drainage patterns in three provinces (India, Brazil, and Africa). Such drainage patterns can be remarkably long-lived (up to at least 200 million years), because, even after the plume-induced uplift has ceased, the crust remains thickened locally, probably as a result of magmatic underplating. K.G. Cox, "The role of mantle plumes in the development of continental drainage patterns," Nature, 342, 873-7, 21/28 December 1989. (University of Oxford, England) The Antarctic meteorite EET87521, now reclassified as a lunar meteorite, is the first known to have come from the lunar maria. The Antarctic lunar meteorites collected earlier all originated in the lunar highlands. J.S. Delaney, "Lunar basalt breccia identified among Antarctic meteorites," Nature, 342, 889-90, 21/28 December 1989. (Rutgers University, New Brunswick, N.J.) Author: MARYE ANNE FOX Department of Chemistry University of Texas Austin Electron-transfer induced configurational change at noncarbon chiral centers can be induced under either oxidative or reductive conditions. This mode of activation produces enormous acceleration of epimerization when compared with thermal routes. H. Brunner, K. Fisch, P.G. Jones, J. Salbeck, "Thermal and electrocatalytic epimerization at iron as the chiral center," Angewandte Chemie, International Edition in English, 28, 1521-3, November 1989. (Universität Regensburg, W.Ger.; Technischen Universität Braunschweig, W.Ger.) Work that was presented during the spring 1989 American Chemical Society meeting in Dallas highlights desirable molecular features, which might lead simultaneously to the control of electronic coupling within ferromagnetic polymers and to spin communication among chains. Several general units to be used as monomers producing materials with permanent magnetic moments have been proposed. D.A. Dougherty, "New designs for very high spin hydrocarbons," Molecular Crystals and Liquid Crystals, 176, 25-31, 1989. (California Institute of Technology, Pasadena) Discussion of the possibility that folding may be controlled by weak hydrogen-bond interactions between sigma and pi systems is then applied to predict the optical and conformational properties of terpenes. M. Nishio, M. Hirota, "CH/ã interaction: implications in organic chemistry," Tetrahedron, 45 (23), 7201-45, 1989. (Meiji Seika Kaisha Ltd., Yokohama, Japan; Yokohama National University, Japan) Retention of configuration in the course of the enzyme-catalyzed reaction of chiral [16O, 17O, 18O] phonopyruvate shows that the reaction involves either an unremarkable phospho-enzyme intermediate or the intramolecular participation of the substrate's carboxylate group. S. Freeman, H.M. Seidel, C.H. Schwalbe, J.R. Knowles, "Phosphonate biosynthesis: the stereochemical course of phosphonenolpyruvate phosphomutase," Journal of the American Chemical Society, 111, 9234-5, 20 December 1989. Two examples show that antibodies can behave much like enzymes to accelerate a desired chemical reaction. With transition state analogs as haptens, these articles show, respectively, enhanced redox catalysis and bimolecular [2+4] cycloaddition reactivity. N. Janjic, A. Tramontano, "Antibody-catalyzed redox reaction," Journal of the American Chemical Society, 111, 9109-10, 6 December 1989. (Scripps Clinic, La Jolla, Calif.) D. Hilvert, K.W. Hill, K.D. Nared, M.-T. Auditor, "Antibody catalysis of a Diels-Alder reaction," Journal of the American Chemical Society, 111, 9261-2, 20 December 1990. (Scripps Clinic, La Jolla, Calif.) Author: FRANK A. WILCZEK School of Natural Sciences Institute for Advanced Study Princeton, N.J. Progress in numerical simulations of quantum field theories has been gradual but steady; only when some milestone is passed do we realize how far we have come - and how far we've yet to go. A recent study has passed a definite landmark: that the lattice theory with a fine enough grid does definitely reach the continuum theory, reproducing the classic results of asymptotic freedom quantitatively. The indication is that realistic theory, including fermions, is no better and no worse than the pure gluon theory previously studied in this regard. K. Bitar, A.D. Kennedy, P. Rossi, "QCD á function with dynamical Wilson fermions," Physical Review Letters, 63, 2713-16, 18 December 1989. (Florida State University, Tallahassee; University of California at San Diego, La Jolla) David Gross has written an entertaining piece that raises some profound points regarding the history of attempts to calculate the fine structure constant - an example of a problem that has been transcended rather than solved. D.J. Gross, "On the calculation of the fine-structure constant," Physics Today, 42, 9-11, December 1989. (Princeton University, N.J.) New ideas for microphysical processes as the seed inhomogeneities that triggered the formation of large-scale structures at the time of the Big Bang are explored. N. Turok, "Global texture as the origin of cosmic structure," Physical Review Letters, 63, 2625-8, 11 December 1989. (Princeton University, N.J.) Striking identities between string theories that appear superficially to be very different types have been discovered and heavily studied in the past few years. For instance, theories in which some of the spatial dimensions are made very tiny can turn out to be equivalent to theories in which those same spatial dimensions are universe-size. A new set of such identities, which relates theories containing only strings to theories containing other objects, is presented. J. Dai, R.G. Leigh, J. Polchinski, "New connections between string theories," Modern Physics Letters A, 4, 2073-83, 20 October 1989. (University of Texas, Austin) A work describing the recent Voyager II mission's launched instrument provides an excellent look at cosmic background radiation, the pale lingering afterglow of the Big Bang. S. Gulkis, P.M. Lubin, S.S. Meyer, R.F. Silverberg, "The cosmic background explorer," Scientific American, 262, 132-9, January 1990. (California Institute of Technology, Pasadena; et al.)

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