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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 Ubiquitin (an abundant 76-amino-acid polypeptide responsible for protein turnover in eukaryotes) requires covalent attachment to target proteins to guide proteolysis. Two new heat-shock genes for ubiquitin-conjugating (UBC) enzymes have been identified, cloned, and sequenced in yeast. The products are needed for protein turnover. Previously identified UBC genes affect diverse cellular processes, including DNA repair, sporulation, and G1 to S cell cycle progress. W. Seufert, J. Jentsch, "Ubiquitin-conjugating enzymes UBC4 and UBC5 mediate selective degradation of short-lived and abnormal proteins," EMBO Journal, 9, 543-50, February 1990. (Max-Planck-Gesellschaft, Tübingen, W.Ger.) It is not enough to have the hormone; one needs the receptor as well to study docking and recognition. The nonglycosylated hGH receptor, which was overproduced and excreted into the periplasm of bacteria, appears functionally equivalent in vitro to that purified from human serum. The nonglycosylated receptor recognizes hGH with the same affinity, and mutant versions of both receptors are also equivalent. These will be used to map interactions between the hormone and its receptor. G. Fuh, M.G. Mulkerrin, S. Bass, N. McFarland, et al., "The human growth hormone receptor: secretion from Escherichia coli and disulfide bonding pattern of the extracellular binding domain," Journal of Biological Chemistry, 265, 3111-15, 25 February 1990. (Genentech, South San Francisco, Calif.) Another chapter in the story about how the ends of chromosomes are made comes with the determination that mutant RNAs in the ribozyme telomerase cause the in vivo synthesis of telomeres with mutant residues. Thus, a segment of RNA in the telomerase functions as an informational template for telomere synthesis. The mutations lead to longer or shorter telomeres and then to monster or senescent cells. G.-L. Yu, J.D. Bradley, L.D. Attardi, E.H. Blackburn, "In vivo alteration of telomere sequences and senescence caused by mutated Tetrahymena telomerase RNAs," Nature, 344, 126-32, 8 March 1990. (University of California, Berkeley) Watson compares the Human Genome Project to the 1961 initiative to send a man to the moon. It is a poor (although frequently made) analogy. The genome project certainly costs less and will yield more immediate benefits, but it will not capture the excitement and enthusiasm of the "television generation" in a comparable manner. That will be a problem. J.D. Watson, "The human genome project: past, present, and future," Science, 248, 44-9, 6 April 1990. (National Institutes of Health, Bethesda, Md.; Cold Spring Harbor Laboratory, N.Y.) Author: DENNIS P. CURRAN Department of Chemistry University of Pittsburgh Pittsburgh Previous chemical models of the vitamin B12s-promoted rearrangement of methylmalonate to succinate have shown that a radical mechanism is feasible. It is still difficult, however, to decide whether the actual enzyme catalyzed rearrangement goes through radical intermediates. Some of the most sophisticated model studies conducted to date indicate that it does not. G. Choi, S.-C. Choi, A. Galan, B. Wilk, P. Dowd, "Vitamin B12s-promoted model rearrangement of methylmalonate to succinate is not a free radical reaction," PNAS, 87, 3174-6, April 1990. (University of Pittsburgh) The Sharpless epoxidation is probably the most important catalytic asymmetric reaction in synthesis today, but it succeeds only for allylic alcohols. A new catalytic method promises to significantly extend the scope of asymmetric epoxidations. W. Zhang, J.L. Loebach, S.R. Wilson, E.N. Jacobsen, "Enantioselective epoxidation of unfunctionalized olefins catalyzed by (salen)manganese complexes," Journal of the American Chemical Society, 112, 2801-3, 28 March 1990. (University of Illinois, Urbana) Highly substituted aromatic and heteroaromatic rings are a large, important class of molecules that are usually prepared by adding functional groups one by one to existing aromatic rings. New annulation strategies, in which the fully functionalized aromatic ring is assembled in a single step, promise to offer a powerful alternative. R.L. Danheiser, R.G. Brisbois, J.J. Kowalczyk, R.F. Miller, "An annulation method for the synthesis of highly substituted polycyclic aromatic and heteroaromatic compounds," JACS, 112, 3093-100, 11 April 1990. (Massachusetts Institute of Technology, Cambridge) R.L. Danheiser, D.D. Cha, "Total synthesis of the host defense stimulant maesanin," Tetrahedron Letters, 31, 1527-30, 1990. (MIT, Cambridge) Three papers that coincidentally appear in a single issue of JACS describe recent advances on three of the hottest synthetic targets: FK-506, brevetoxin B, and calicheamicinone. T.K. Jones, R.A. Reamer, R. Desmond, S.G. Mills, "Chemistry of tricarbonyl hemiketals and application of Evans' technology to the total synthesis of the immunosuppressant(-)-FK-506," JACS, 112, 2998-3017, 11 April 1990. (Merck Sharp & Dohme Research Laboratories, Rahway, N.J.) K.C. Nicolaou, C.-K. Hwang, B.E. Marron, S.A. DeFrees, et al., "Bridging of macrodithionalactones to bicyclic systems. Synthesis and modeling of oxapolycyclic frameworks," JACS, 112, 3040-54, 11 April 1990. (University of Pennsylvania, Philadelphia; G.D. Searle Research and Development, Skokie, Ill.) M. Paz Cabal, R.S. Coleman, S.J. Danishefsky, "Total synthesis of calicheamicinone: a solution to the problem of the elusive urethane," JACS, 112, 3253-5, 11 April 1990. (Yale University, New Haven, Conn.) Author: PETER D. MOORE Department of Biology King's College London, U.K. Many mammals are semiaquatic in their habits, but few are prepared to exploit sea water. One exception is the otter. Experiments with pelts and with captive animals have shown that immersion in sea water destroys the fur's capacity to retain air pockets and, hence, reduces its thermal insulation. Otters that swim in the sea need to wash in fresh water afterward. H. Kruuk, D. Balharry, Effects of sea water on thermal insulation of the otter, Lutra lutra," Journal of Zoology, 220, 405-15, March 1990. (Institute of Terrestrial Ecology, Banchory, Scotland) Relatively few studies have been carried out on the correlation between the population density of a plant predator (herbivore) and its prey (plant). On the Isle Royale, the extent of moose browsing damage on balsam fir is correlated with both high moose density and low fir density. The moose first arrived on the island early this century, and the continued recruitment and survival of the fir is now threatened in some areas. T.A. Brandner, R.O. Peterson, K.L. Risenhoover, "Balsam fir on Isle Royale: effects of moose herbivory and population density," Ecology, 71, 155-64, February 1990. (Michigan Technological University, Houghton) The early bird may catch the worm, or it may forgo the pleasure and concentrate on singing instead. A well-fed blackbird sings earlier in the day than do its rivals, thus neglecting foraging for the sake of defending its territory. Early singing is also correlated with peak fertility, so performance in the dawn chorus holds many clues for females concerning the condition of their males. I.C. Cuthill, W.A. Macdonald, "Experimental manipulation of the dawn and dusk chorus in the blackbird Turdus merula," Behavioral Ecology and Sociobiology, 26, 209-16, March 1990. (Edward Grey Institute of Field Ornithology, Oxford, England) One of the most widely quoted examples of interspecific cooperation between vertebrates has now been called into question. Evidence for the relationship between the greater honeyguide and the honey badger is actually very slim and largely anecdotal. Perhaps it was early human populations that were led to bee nests by the honeyguide and subsequently disturbed the site, making food available. But if this is so, will the honeyguide be threatened by decreases in the subsistence activities of human populations in Africa? W.R.J. Dean, W.R. Siegfried, I.A.W. Macdonald, "The fallacy, fact, and fate of guiding behavior in the greater honeyguide," Conservation Biology, 4, 99-101, March 1990. (University of Cape Town, South Africa) Author: THEODORE DAVIDSON Institute of Materials Science University of Connecticut Storrs Using polymers as precursors to ceramics offers some attractive possibilities. Polymers can be drawn into fibers or cast as films and then converted to ceramic materials. This has been accomplished already with carbon and SiC fibers and coatings. A recent synthesis of soluble polymers from the six-membered borazine ring has provided a precursor for boron nitride powder. Subsequent development could produce fibers or coatings. P.J. Fazen, J.S. Beck, A.T. Lynch, E.E. Remsen, L.G. Sneddon, "Thermally induced borazine dehydropoly-merization reactions. Synthesis of a new high-yield polymeric precursor to boron nitride," Chemistry of Materials, 2 (2), 96-7, 1990. (University of Pennsylvania, Philadelphia) In response to the concern over brittleness in oxide glasses, numerous strengthening approaches are examined. Surface modifications reduce the influence of surface defects, while bulk composition, phase separation, and fiber or particulate reinforcement may increase both strength and fracture toughness. Successes and limitations are evenly presented. I.W. Donald, "Methods for improving the mechanical properties of oxide glasses," Journal of Materials Science, 24, 4177-208, December 1989. (Atomic Weapons Establishment, Aldermaston, Berkshire, England) Controlling microstructure is a principal objective in much of materials science. Recently, several approaches have been taken to selectively place a second phase "guest" species in an ordered array of "host" molecules. With iron oxychloride (FeOCl) as the host lattice, intercalation can be achieved with species that transfer charge from guest to host. An interesting example involves aromatic hydrocarbons, such as perylene and tetracene. When these are intercalated into FeOCl, they raise the electrical conductivity of the host by a factor of 105. The resulting low-dimensional semiconductors have band gaps near 0.28 electron volts. J.F. Bringley, B.A. Averill, "Aromatic iron intercalates: synthesis and characterization of iron oxychloride intercalated with perylene and tetracene," Chemistry of Materials, 2, 180-6, March/April 1990. (University of Virginia, Charlottesville) In another host-guest situation, nanoparticles of cadmium sulfide can be sandwiched between the headgroups of an ordered organic array. Long-range order is created by dipping up a Langmuir-Blodgett (L-B) film of dioctadecyldimethylam-monium chloride, adsorbing the CdS particles, and closing with a second L-B film. Measurements by low-energy electron diffraction, absorption spectroscopy, and scanning tunneling microscopy show that the cadmium sulfide retains its crystallinity and the multilayer forms a structured array. S. Xu, X.K. Zhao, J. H. Fendler, "Ultrasmall semiconductor particles sandwiched between surfactant headgroups in Langmuir-Blodgett films," Advanced Materials, 2 (4), 183-5, 1990. (Syracuse University, N.Y.) The scanning tunneling microscope has opened new vistas from fundamental studies of single crystal surfaces to biological ultrastructure at the macromolecular level. It has also inspired a whole generation of new techniques in which the spatial resolution is better than the wavelength used for imaging. There are magnetic and electrostatic force microscopies; near-field optical, thermal, and acoustic microscopies -- each with special capabilities. These are reviewed -- with their limitations. And, included in the same issue are 136 other papers that were presented at the Fourth International Conference on Scanning Tunneling Microscopy/Spectroscopy. H.K. Wickramasinghe, "Scanning probe microscopy: current status and future trends," Journal of Vacuum Science and Technology, 8A, 363-8, January/February 1990. (IBM Watson Research Center, Yorktown Heights, N.Y.)

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