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231.
Donnelly CA Woodroffe R Cox DR Bourne J Gettinby G Le Fevre AM McInerney JP Morrison WI 《Nature》2003,426(6968):834-837
Pathogens that are transmitted between wildlife, livestock and humans present major challenges for the protection of human and animal health, the economic sustainability of agriculture, and the conservation of wildlife. Mycobacterium bovis, the aetiological agent of bovine tuberculosis (TB), is one such pathogen. The incidence of TB in cattle has increased substantially in parts of Great Britain in the past two decades, adversely affecting the livelihoods of cattle farmers and potentially increasing the risks of human exposure. The control of bovine TB in Great Britain is complicated by the involvement of wildlife, particularly badgers (Meles meles), which appear to sustain endemic infection and can transmit TB to cattle. Between 1975 and 1997 over 20,000 badgers were culled as part of British TB control policy, generating conflict between conservation and farming interest groups. Here we present results from a large-scale field trial that indicate that localized badger culling not only fails to control but also seems to increase TB incidence in cattle. 相似文献
232.
Biofilms are surface-attached microbial communities with characteristic architecture and phenotypic and biochemical properties distinct from their free-swimming, planktonic counterparts. One of the best-known of these biofilm-specific properties is the development of antibiotic resistance that can be up to 1,000-fold greater than planktonic cells. We report a genetic determinant of this high-level resistance in the Gram-negative opportunistic pathogen, Pseudomonas aeruginosa. We have identified a mutant of P. aeruginosa that, while still capable of forming biofilms with the characteristic P. aeruginosa architecture, does not develop high-level biofilm-specific resistance to three different classes of antibiotics. The locus identified in our screen, ndvB, is required for the synthesis of periplasmic glucans. Our discovery that these periplasmic glucans interact physically with tobramycin suggests that these glucose polymers may prevent antibiotics from reaching their sites of action by sequestering these antimicrobial agents in the periplasm. Our results indicate that biofilms themselves are not simply a diffusion barrier to these antibiotics, but rather that bacteria within these microbial communities employ distinct mechanisms to resist the action of antimicrobial agents. 相似文献
233.
The codon 72 polymorphic variants of p53 have markedly different apoptotic potential 总被引:31,自引:0,他引:31
The gene TP53, encoding p53, has a common sequence polymorphism that results in either proline or arginine at amino-acid position 72. This polymorphism occurs in the proline-rich domain of p53, which is necessary for the protein to fully induce apoptosis. We found that in cell lines containing inducible versions of alleles encoding the Pro72 and Arg72 variants, and in cells with endogenous p53, the Arg72 variant induces apoptosis markedly better than does the Pro72 variant. Our data indicate that at least one source of this enhanced apoptotic potential is the greater ability of the Arg72 variant to localize to the mitochondria; this localization is accompanied by release of cytochrome c into the cytosol. These data indicate that the two polymorphic variants of p53 are functionally distinct, and these differences may influence cancer risk or treatment. 相似文献
234.
The RAD6 pathway is central to post-replicative DNA repair in eukaryotic cells; however, the machinery and its regulation remain poorly understood. Two principal elements of this pathway are the ubiquitin-conjugating enzymes RAD6 and the MMS2-UBC13 heterodimer, which are recruited to chromatin by the RING-finger proteins RAD18 and RAD5, respectively. Here we show that UBC9, a small ubiquitin-related modifier (SUMO)-conjugating enzyme, is also affiliated with this pathway and that proliferating cell nuclear antigen (PCNA) -- a DNA-polymerase sliding clamp involved in DNA synthesis and repair -- is a substrate. PCNA is mono-ubiquitinated through RAD6 and RAD18, modified by lysine-63-linked multi-ubiquitination--which additionally requires MMS2, UBC13 and RAD5--and is conjugated to SUMO by UBC9. All three modifications affect the same lysine residue of PCNA, suggesting that they label PCNA for alternative functions. We demonstrate that these modifications differentially affect resistance to DNA damage, and that damage-induced PCNA ubiquitination is elementary for DNA repair and occurs at the same conserved residue in yeast and humans. 相似文献
235.
Percy KE Awmack CS Lindroth RL Kubiske ME Kopper BJ Isebrands JG Pregitzer KS Hendrey GR Dickson RE Zak DR Oksanen E Sober J Harrington R Karnosky DF 《Nature》2002,420(6914):403-407
Human activity causes increasing background concentrations of the greenhouse gases CO2 and O3. Increased levels of CO2 can be found in all terrestrial ecosystems. Damaging O3 concentrations currently occur over 29% of the world's temperate and subpolar forests but are predicted to affect fully 60% by 2100 (ref. 3). Although individual effects of CO2 and O3 on vegetation have been widely investigated, very little is known about their interaction, and long-term studies on mature trees and higher trophic levels are extremely rare. Here we present evidence from the most widely distributed North American tree species, Populus tremuloides, showing that CO2 and O3, singly and in combination, affected productivity, physical and chemical leaf defences and, because of changes in plant quality, insect and disease populations. Our data show that feedbacks to plant growth from changes induced by CO2 and O3 in plant quality and pest performance are likely. Assessments of global change effects on forest ecosystems must therefore consider the interacting effects of CO2 and O3 on plant performance, as well as the implications of increased pest activity. 相似文献
236.
给出具有内自同构群G,作为Galois群的C上的中心Galois代数A的所有这样的C—可分子代数T所构成的集合,这里T的换位子是投射子群代数,与G的所有子群所构成的集合之间的一一对应关系,并且还给出这些投射子群代数及其在A中的换位子的一些性质。 相似文献
237.
测定了来自4个不同地点(包括安徽宣城野生和饲养种群、浙江长兴的饲养种群及在美国的饲养种群)的64个扬子鳄线粒体DNA控制区部分序列.结果共检测出4个单倍型共3个变异位点,与龟类、鸟类、哺乳类及其它鳄类相比较,反央出扬子鳄线粒体区的序列变异性很低.在此基础上,对扬子鳄遗传保护提出了有关建议. 相似文献
238.
Here we evaluate the generalizability of calibration studies which have used general knowledge questions, and argue that on conceptual, methodological and empirical grounds the results have limited applicability to judgemental forecasting. We also review evidence which suggests that judgemental forecast probabilities are influenced by variables such as the desirability, imminence, time period and perceived controllability of the event to be forecast. As these variables do not apply to judgement in the domain of general knowledge, a need for research recognizing and exploring the psychological processes underlying uncertainty about the future is apparent. 相似文献
239.
P Cuisinier-Gleizes A George M Thomasset H Mathieu 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1975,280(18):2145-2148
Chronic metabolic acidosis entails hyperparathyroidism and osteopathy. In order to elucidate the role of the thyroparathyroids in this bone lesion production the effects of acidic diet for 7 weeks were studied in parathyroidectomized (PTX), thyroparathyroidectomized (TPTX) and shamoperated (Sh-O) growing rats. In all animals urinary excretion of calcium, phosphate, ammonium and titrable acidity was similarly increased. The rise in hydroxyproline excretion and urinary 85-sr (that was injected previous to acidic feeding) was more marked in PTX and TPTX rats. Moreover, in these animals the serum calcium level was increased, the blood pH was decreased. According to these data, an acidic diet intake that is not sufficient to elicit a fall in blood pH of normal young rats can induce severe acidosis in chronically parathyroidectomized or thyroparathyroidectomized animals; moreover the bone resorption appears more marked. It is concluded that parathyroids are involved in the extra-cellular fluid defense mechanism against acidosis by a no bone resorptive mechanism. We hypothesize that the parathyroids permit the necessary and adequate supply of bicarbonates by the bone to maintain blood pH homeostasis. 相似文献
240.