immobile and thus less harmful. So sci al process is by far the most entists are keenly interested in process important pathway for Cr(VI) es that reduce Cr(VI) species to Cr(III) reduction in geological materi as potential environmental remediators. als. Thanks to the ΙΟ-μιη spa It is known that some natural metal ox tial resolution afforded by the ides and organic molecules can do the brightness of IR light obtained job in geological environments. In addi from the ALS, the group could tion, certain types of bacteria appear to produce spectromicroscopic not only thrive in a toxic environment of "images" whose peaks and val Cr(VT), but to reduce it to the less mo leys show the locations of the bile and less harmful form as well. action. Fortuitously, a protein New insight into the Cr(VT)-reducing in the bacteria, the chromium abilities of these bacteria comes from species, and toluene all have staff scientist Hoi-Ying Holman and col well-characterized IR absorp Holman (foreground) with physicists Wayne leagues at Lawrence Berkeley National tion bands. Most important, McKinney (upper left) and Michael Martin (far right), Laboratory in Berkeley, Calif. Using the IR light, despite its bright who built the IR beamline apparatus used in the LBNL's bright Advanced Light Source ness, doesn't destroy the bac chromium reduction experiments. (ALS), they monitored in real time and teria, as many other analytical with unprecedented resolution a bacteri techniques used to study these types of previously only been seen in special lab oratory microbial systems. al colony and the disappearance of Cr (VI) systems do. Holman and colleagues also exposed and corresponding appearance of Cr (III). After five days of coexisting with a Their study, to appear in the October chromate solution on a smooth piece of native bacterial colonies to chromate so issue of Geomicrobiology (published bymagnetite (a mixture of iron oxides), a lution on the ragged surfaces of Colum bia basalt rock chips taken from the Taylor & Francis), shows that the bacteri- sample of the bactenaArthrobacter oxydans reduced a good portion of the Cr(VT). By boundary of a contaminated area. They contrast, a control magnetite sample with found that after four months, some of no bacteria had little effect on the Cr (VI). the colonies were thriving in Cr(III) And a sample of the bacteria to which the compounds, and the Cr(VT) was gone. Holman's work represents "a good group added toluene reduced even great er amounts of Cr(VI). The authors sus first step" toward applying new surface pect the toluene may provide food for the chemistry analysis techniques to the bacteria. Additionally, the bacteria de study of environmental microbial pro grade toluene to produce catechol and cesses, says Derek R. Lovley, head of other smaller molecules that themselves the microbiology department at the Uni versity of Massachusetts, Amherst. "In are reducing agents, Holman says. Two mysterious new peaks arose in my opinion, this will be an important the spectra that the researchers later emerging area in environmental micro determined were probably from a Cr(V) biology over the next several years." Protein amirta II Elizabeth Wilson compound, an intermediate that had
AAAS forum supports st m cell research
Chromate
Spectromicroscopy measurements show the spatial distribution of bac teria, indicated by protein amide II (top), and chromate (bottom) on a magnetite sample, after five days. The low chromate levels correspond to the location of the bacteria.
Research on the use of embryonic stem cells to treat human diseases should proceed with federal support, according to the American Association for the Ad vancement of Science. In a just-released draft report, pre pared in conjunction with the Institute for Civil Society, Newton, Mass., AAAS states that stem cells—the undifferenti ated cells found in embryos, and, in very limited quantities, in adults—have shown enormous potential to relieve hu man suffering and treat diseases rang ing from various forms of cancer to Alz heimer's disease. But, it goes on to say, the research needed to make such treat ments practical is being stifled due to ethical and religious objections. Because of such objections, Con gress has banned federal support for re-
search that uses cells obtained from aborted fetuses or from embryos fertil ized at in vitro fertilization clinics. AAAS argues that the derivation of the cells—that is, collection of embryon ic tissue—can be ethically separated from using the resulting cell lines for re search. The report contends that many ethical issues could be resolved by en suring that no one profits directly from the destruction of embryos. Federal funding of all forms of stem cell research—a central recommenda tion of the AAAS report—would be quite beneficial, argues Audrey R. Chap man, director of the AAAS Dialogue on Science, Religion & Ethics program. 'The commitment of federal funds," she explains, "provides a basis for review and oversight of the research" that AUGUST 30,1999 C&EN
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n e w s of t h e w e e k would be lost if such research was supported solely by private funding. And federal support would allow the research to move forward swiftly. As part of its effort to emphasize the importance of the science and minimize the controversial ethical and religious issues surrounding stem cell research, AAAS sponsored a public forum in Washington, D.C., last week to educate people on the issues and obtain reaction to its draft report. The forum doesn't seem to have changed many minds. The few participants who still voiced opposition to stem cell research did so on moral grounds. They did not object to research involving adult stem cells, only that involving fetal stem cells.
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thought they ought to—and indeed they have—but we weren't sure." The structures have resolutions of 5 A and 5.5 A, not fine enough to locate individual atoms. But they do allow previously identified parts of the subunits, such as individual proteins or helical coils of RNA, to be pinpointed within the subunit as a whole. That allows researchers to begin to speculate on the basis of position what the functions must be of both the RNA and protein components. In both subunits, it's the RNA that seems to be at the center of things. Nearly all the proteins in the 30S subunit, for instance, are located away from the functionally important part of the ribosome, which is the interface between the two subunits. The structure "supports speculations that a primordial ribosome could have contained no protein at all," Ramakrishnan and his coMolecular biologists are getting their stand the mechanism of protein synthe- workers write. However, they add, at first clear look at what many of them sis in the absence of this structure, Noller least a few ribosomal proteins in the 30S subunit may be more directly involved consider the most complicated machine explains. in ribosomal function than previously ever assembled. The machine is the riThe ribosome is so huge that there bosome, the protein-synthesizing facto- has long been a question as to whether its suspected. "It is likely that not all of the ry found in all living cells. The picture of structure would be solvable at all by X-ray moving parts and crucial surfaces in the how it's put together comes from two X- diffraction methods. With a total molecu- ribosome of today will be found to conray crystal structures, one of each of the lar weight of around 1.7 million, it is a sist of RNA," they suggest. primary subunits from bacteria. These structures show how an RNA hundred times larger than a typical proThomas A. Steitz led the team that tein. It is completely asymmetric and con- can be folded and wrapped to make a determined the structure of the larger tains in its two subunits three RNA mole- large 3-D structure, Steitz notes. Among subunit, called the 50S subunit. Steitz is cules and 56 different proteins. the more surprising aspects of that proa professor of molecular biophysics, bio'The thing that held us back," Steitz cess, he says, is that "there are duplex chemistry, and chemistry at Yale Uni- now says, "apart from some technical rods of RNA running through the whole versity and a Howard Hughes Medical problems that were challenging, was 50S subunit that are cross-linked by RNA Institute investigator. The structure of our uncertainly as to whether it was do- structure and also by proteins. The prothe smaller subunit, called 30S, was de- able. These subunits are so much big- teins are clearly functioning as structural termined by a team led by Venki Ra- ger than any other asymmetric object elements, in large part They may have othmakrishnan of the University of Utah whose structure has been determined er functions as well, but that is certainly School of Medicine, Salt Lake City, and that we were just unsure as to whether one of the things they are doing." the Medical Research Center Laboratory the standard methods would work. We Although the current structures proof Molecular Biology, vide enough informaCambridge, U.K. [Nature, tion to stimulate many 400, 833 and 841(1999)]. years of experimentaBoth teams used the Nation to try to pin down tional Synchrotron Light the exact mechanism of Source, located at Brookprotein synthesis, even haven National Laboratobetter structures are ry, Upton, N.Y. expected soon. At a ribosome conference "The ribosome field earlier this summer, has been waiting for this sort of structural work for Noller described a crysdecades," says Harry Noltal structure of the two ler, professor of molecusubunits together at lar biology at the Univer7.8-À resolution, and sity of California, Santa Steitz says he is well Cruz. Because the riboalong toward atomic some itself is so complex, X-ray structures reveal the massive size and complexity of large (right) and scale resolution of the as are the processes it car- small subunits of bacterial ribosome. Some key regions of double-stranded structure of the 50S ries out, it has been ex- RNA (double helices) and protein (ribbons) have been superimposed over subunit. tremely difficult to under- the space-filling models for each subunit. Rebecca Rawls AAAS will take the forum into account as itfinalizesits report, which is expected to be released by the end of September. The results of two government reviews of the issue are also imminent. The President's National Bioethics Advisory Commission's final study, which likely will recommend federal funding of stem cell research, is scheduled for release within a few weeks. And the National Institutes of Health is expected to say how it will proceed with respect to funding this research at about the same time (C&EN, April 26, page 20). Copies of the AAAS draft study are available at (www.aaas.org/spp/dspp/ sfrl/projects/stem/main.htm). David Hanson
Complex structure of ribosome solved
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