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991.
Growth of the human breast cancer cell line MCF-7 is enhanced by androgens, but only at pharmacological concentrations. Although physiological concentrations of androgens translocate the androgen receptor into the nucleus, no mitogenic effects are observed. By contrast, pharmacological androgens translocate not only the androgen receptor but also the estrogen receptor, and at these high doses significantly increase both DNA and estrogen-dependent protein synthesis. We therefore propose that androgens stimulate MCF-7 cell growth not through the androgen receptor but rather through the estrogen receptor. 相似文献
992.
The current interest in locating new or alternative sources of energy has focused attention on solar energy capture by crops that can be subsequently utilized as a substitute for fossil fuels. The very high productivity of sugarepane and the fact that it accumulates sugars that are directly fermentable to alcohol may have caused seemingly less productive crops to be overlooked. We show here that recoverable alcohol from achievable commercial yields of pineapple can actually equal that of sugarcane, with the pineapple crop requiring only a fraction of the water used by sugarcane. Pineapple is well adapted to the subhumid or semiarid tropics and thus is particularly well suited for exploiting large areas not now under cultivation with any crop of commercial value. 相似文献
993.
Lahav O Naim A Buta RJ Corwin HG de Vaucouleurs G Dressler A Huchra JP van den Bergh S Raychaudhury S Sodré L Storrie-Lombardi MC 《Science (New York, N.Y.)》1995,267(5199):859-862
The quantitative morphological classification of galaxies is important for understanding the origin of type frequency and correlations with environment. However, galaxy morphological classification is still mainly done visually by dedicated individuals, in the spirit of Hubble's original scheme and its modifications. The rapid increase in data on galaxy images at low and high redshift calls for a re-examination of the classification schemes and for automatic methods. Here are shown results from a systematic comparison of the dispersion among human experts classifying a uniformly selected sample of more than 800 digitized galaxy images. These galaxy images were then classified by six of the authors independently. The human classifications are compared with each other and with an automatic classification by an artificial neural network, which replicates the classification by a human expert to the same degree of agreement as that between two human experts. 相似文献
994.
Slobodkin LB 《Science (New York, N.Y.)》1988,242(4879):784-785
995.
Gillooly JF Brown JH West GB Savage VM Charnov EL 《Science (New York, N.Y.)》2001,293(5538):2248-2251
We derive a general model, based on principles of biochemical kinetics and allometry, that characterizes the effects of temperature and body mass on metabolic rate. The model fits metabolic rates of microbes, ectotherms, endotherms (including those in hibernation), and plants in temperatures ranging from 0 degrees to 40 degrees C. Mass- and temperature-compensated resting metabolic rates of all organisms are similar: The lowest (for unicellular organisms and plants) is separated from the highest (for endothermic vertebrates) by a factor of about 20. Temperature and body size are primary determinants of biological time and ecological roles. 相似文献
996.
Role of adenine nucleotide translocator 1 in mtDNA maintenance 总被引:1,自引:0,他引:1
Kaukonen J Juselius JK Tiranti V Kyttälä A Zeviani M Comi GP Keränen S Peltonen L Suomalainen A 《Science (New York, N.Y.)》2000,289(5480):782-785
Autosomal dominant progressive external ophthalmoplegia is a rare human disease that shows a Mendelian inheritance pattern, but is characterized by large-scale mitochondrial DNA (mtDNA) deletions. We have identified two heterozygous missense mutations in the nuclear gene encoding the heart/skeletal muscle isoform of the adenine nucleotide translocator (ANT1) in five families and one sporadic patient. The familial mutation substitutes a proline for a highly conserved alanine at position 114 in the ANT1 protein. The analogous mutation in yeast caused a respiratory defect. These results indicate that ANT has a role in mtDNA maintenance and that a mitochondrial disease can be caused by a dominant mechanism. 相似文献
997.
New method for detecting cellular transforming genes 总被引:24,自引:0,他引:24
D G Blair C S Cooper M K Oskarsson L A Eader G F Vande Woude 《Science (New York, N.Y.)》1982,218(4577):1122-1125
Tumor induction in athymic nude mice can be used to detect dominant transforming genes in cellular DNA. Mouse NIH 3T3 cells freshly transfected with either cloned Moloney sarcoma proviral DNA or cellular DNA's derived from virally transformed cells induced tumors when injected into athymic nu/nu mice. Tumors were also induced by cells transfected with DNA from two tumor-derived and one chemically transformed human cell lines. The mouse tumors induced by human cell line DNA's contained human DNA sequences, and DNA derived from these tumors was capable of inducing both tumors and foci on subsequent transfection. Tumor induction in nude mice represents a useful new method for the detection and selection of cells transformed by cellular oncogenes. 相似文献
998.
999.
Officer CB Biggs RB Taft JL Cronin LE Tyler MA Boynton WR 《Science (New York, N.Y.)》1984,223(4631):22-27
Anoxia occurs annually in deeper waters of the central portion of the Chesapeake Bay and presently extends from Baltimore to the mouth of the Potomac estuary. This condition, which encompasses some 5 billion cubic meters of water and lasts from May to September, is the result of increased stratification of the water column in early spring, with consequent curtailment of reoxygenation of the bottom waters across the halocline, and benthic decay of organic detritus accumulated from plankton blooms of the previous summer and fall. The Chesapeake Bay anoxia appears to have had significant ecological effects on many marine species, including several of economic importance. 相似文献
1000.
M.L. Leamy 《Geoderma》1975,13(1):53-60
Field and laboratory methods used for the identification of paleosols in New Zealand are discussed, and examples are given of their application to both buried and relict paleosols. Field methods include a pedomorphic index based on the quantitative assessment of four or more selected diagnostic properties for each horizon, which is useful under certain conditions to express the relative degree of development of several profiles.The significance of paleosol identification is only fully appreciated when the paleosol is defined stratigraphically and interpreted in terms of time and environment. The basis for defining soil-stratigraphic units in parts of New Zealand is outlined. 相似文献