Undesirable Fragmentation Research Articles

DNA Bending Is Essential for the Site-specific Recognition of DNA Response Elements by the DNA Binding Domain of the Tumor Suppressor Protein p53

We have used circular permutation assays to determine the extent and location of the DNA bend induced by the DNA binding domain of human wild type p53 (p53DBD) upon binding to several naturally occurring DNA response elements. We have found that p53DBD binding induces axial bending in all of the response elements investigated. In particular, response elements having a d(CATG) sequence at the junction of two consensus pentamers in each half-site favor highly bent complexes (bending angle is approximately 50 degrees ), whereas response elements having d(CTTG) bases at this position are less bent (bending angles from approximately 37 to approximately 25 degrees ). Quantitative electrophoretic mobility shift assays of different complexes show a direct correlation between the DNA bending angle and the binding affinity of the p53DBD with the response elements, i.e. the greater the stability of the complex, the more the DNA is bent by p53DBD binding. The study provides evidence that the energetics of DNA bending, as determined by the presence or absence of flexible sites in the response elements, may contribute significantly to the overall binding affinity of the p53DBD for different sequences. The results therefore suggest that both the structure and the stability of the p53-DNA complex may vary with different response elements. This variability may be correlated with variability in p53 function.

Use of spatial prediction techniques and fuzzy classification for mapping soil pollutants

High concentration of heavy metals caused by soil pollution processes vary in a three-dimensional space. This study focuses on a strip of land which was sampled at three different depths. Fuzzy classification by fuzzy k-means was used to analyze the spatial variability for each separate layer. The concentrations of heavy metals showed abrupt changes in geographical space and the coefficients of variation were high, but in most of the area more gradual transitions in concentrations of heavy metals were found. To avoid undesirable fragmentation in the classification, i.e. a lot of small pieces of land, spatial variability is used by including additional predicted values of Cu, Pb and Zn representing spatial correlation in the horizontal and vertical plane. Membership values are interpolated for each class by ordinary kriging. For all situations the different maps are integrated into a final classification map with associated impurity map. The effect of observation density, class uncertainty and fuzziness exponent is expressed on the impurity map. A comparison is made between fuzzy classification and probability based mapping by indicator kriging.

The Engineers: A History of the Engineering Profession in Britain, 1750–1914 by R. A. Buchanan

TECHNOLOGY AND CULTURE Book Reviews 143 The Engineers: A History of the Engineering Profession in Britain, 1750— 1914. By R. A. Buchanan. London: Jessica Kingsley, 1989. Pp. 240; notes, appendix, bibliography, index. £25.00. In producing a pioneering study of the professional development of engineering in Britain, R. A. Buchanan has chosen to write a brief, useful introductory sketch, rather than attempting a more extended, definitive treatment. In his first chapter, the author discusses the scope of engineering history, and he attempts to get beyond the handful of famous engineers who dominate the historical literature to the hundreds of little-known figures who have contributed more, in the aggregate, than the few prominent leaders. His statistical analysis of biographical data on British engineers is helpful and insightful. The author’s coverage is quite broad. The story of the emergence and growth of the engineering profession (in chapters 2 and 3) is told in the context of the history of British engineering. While this contextual approach is a source of strength, the historical materials are of necessity sketchy and anecdotal and are dominated by a few heroic engineers, restoring the view that the author sought to avoid in his first chapter. However, many of the individuals discussed and incidents noted are well chosen and illuminating. A useful bibliogra­ phy includes data on twenty-two leading British engineering societies, as well as a valuable listing of the extensive secondary literature. Chapters 4—6 deal with the formation of new specialized societies, leading, in the author’s view, to an undesirable fragmentation of British engineering. In chapter 7, Buchanan discusses the rise and (in his view) regrettable decline of regional and local associations of engineers in modern times. The eighth chapter is a condensation of the author’s article “The Diaspora of British Engineering,” which appeared in Technology and Culture (vol. 27 [July 1986]: 501—24). Two of the most useful (and most disappointing) chapters are 9 and 10, which deal with engineering education and with the “Ideas and Beliefs of the Engineers.” The final chapter addresses 20th-century developments, relating them to the material in earlier chapters. Emphasizing the author’s brevity is the fact that he refers the reader to the secondary literature for some of the most important themes (although he does not totally neglect them). Thus, for the scientific and technological education of engineers in 19th-century Britain, Buchanan states, “There have been several studies ... so that it is not necessary to rehearse this theme here” (p. 161). The author fails to do justice to the important scientific achievements of British engineers. There is no mention of such important figures as Robert Willis or Oliver Heaviside (and many others). This deficiency is also a result of brevity, at least in part; the author has treated the scientific achievements of British engineers more effectively in a previous 144 Book Reviews TECHNOLOGY AND CULTURE paper, “The Rise of Scientific Engineering in Britain,” published in the British Journalfor the History of Science (July 1985, pp. 218—33). A more definitive social history would include a study of the culture of British engineering. But this book is useful and interesting, and it should provide future scholars in this field with a valuable point of departure. Edwin T. Layton, Jr. Dr. Layton is professor of the history of technology in the Department of Mechanical Engineering at the University of Minnesota. History ofHeat Transfer: Essays in Honor ofthe 50th Anniversary ofthe ASME Heat Transfer Division. Edited by Edwin T. Layton, Jr., and John H. Lienhard. New York: American Society of Mechanical Engineers, 1988. Pp. viii + 260; illustrations, references. $40.00 (paper). The first law of thermodynamics establishes a relationship between heat and work and the second law of thermodynamics states that heat flows only from a hot body to a cold body and never in the reverse direction. However, thermodynamics is totally silent on the question of the rate at which heat travels. In order to design hardware that involves the transfer of heat from one place to another, engineers need to be able to predict rates of heat transfer per unit of surface area. Thus has the engineering science of heat transfer evolved during...

Char formation in polyvinyl chloride. III. Mechanistic aspects of isothermal degradation of PVC containing some dehydrochlorination/charring agents

We pyrolyzed PVC with and without the char-promoters iron (III) pyromellitate, zinc pyromellitate, and MoO3 (1 phr) under isothermal conditions (207°C, nitrogen) and analyzed the soluble and insoluble residues to characterize the reactions important to charring. Both pyromellitates, apparently acting as their metal chlorides, catalyze dehydrochlorination and crosslinking that could lead to rapid charring; however, the zinc additive also catalyzes undesirable fragmentation. MoO3, possibly acting as an oxychloride, has only a small effect on PVC degradation under the conditions used; however, it does suppress fragmentation. The relative rates of crosslinking to fragmentation are important in determining char yields.