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951.
Anti-Latour 总被引:2,自引:0,他引:2
Bloor D 《Studies in history and philosophy of science》1999,30(1):81-112
952.
Bacterial suicide through stress 总被引:9,自引:0,他引:9
Outside of the laboratory, bacterial cells are constantly exposed to stressful conditions, and an ability to resist those
stresses is essential to their survival. However, the degree of stress required to bring about cell death varies with growth
phase, amongst other parameters. Exponential phase cells are significantly more sensitive to stress than stationary phase
ones, and a novel hypothesis has recently been advanced to explain this difference in sensitivity, the suicide response. Essentially,
the suicide response predicts that rapidly growing and respiring bacterial cells will suffer growth arrest when subjected
to relatively mild stresses, but their metabolism will continue: a burst of free-radical production results from this uncoupling
of growth from metabolism, and it is this free-radical burst that is lethal to the cells, rather than the stress per se. The
suicide response hypothesis unifies a variety of previously unrelated empirical observations, for instance induction of superoxide
dismutase by heat shock, alkyl-hydroperoxide reductase by osmotic shock and catalase by ethanol shock. The suicide response
also has major implications for current [food] processing methods.
Received 29 March 1999; received after revision 14 May 1999; accepted 17 May 1999 相似文献
953.
Cole DG 《Cellular and molecular life sciences : CMLS》1999,56(3-4):217-226
The kinesins constitute a large family of motor proteins which are responsible for the distribution of numerous organelles, vesicles and macromolecular complexes throughout the cell. One class of these molecular motors, kinesin-II, is unique in that these proteins are typically found as heterotrimeric complexes containing two different, though related, kinesin-like motor subunits, and a single nonmotor subunit. The heteromeric nature of these kinesins appears to have resulted in a class of combinatorial kinesins which can 'mix and match' different motor subunits. Another novel feature of these motors is that the activities of several kinesin-II representatives are essential in the assembly of motile and nonmotile cilia, a role not attributed to any other kinesin. This review presents a brief overview of the structure and biological functions of kinesin-II, the heteromeric kinesin. 相似文献
954.
Immune responses to DNA vaccines 总被引:16,自引:0,他引:16
DNA vaccines, based on plasmid vectors expressing an antigen under the control of a strong promoter, have been shown to induce
protective immune responses to a number of pathogens, including viruses, bacteria and parasites. They have also displayed
efficacy in treatment or prevention of cancer, allergic diseases and autoimmunity. Immunologically, DNA vaccines induce a
full spectrum of immune responses that include cytolytic T cells, T helper cells and antibodies. The immune response to DNA
vaccines can be enhanced by genetic engineering of the antigen to facilitate its presentation to B and T cells. Furthermore,
the immune response can be modulated by genetic adjuvants in the form of vectors expressing biologically active determinants
or by more traditional adjuvants that facilitate uptake of DNA into cells. The ease of genetic manipulation of DNA vaccines
invites their use not only as vaccines but also as research tools for immunologists and microbiologists.
Received 26 October 1998; received after revision 3 December 1998; accepted 3 December 1998 相似文献
955.
A population of ventral neural tube cells has recently been shown to migrate out of the hind brain neural tube via the vagus
nerve and contribute to the developing gastrointestinal tract. Since liver is also innervated by the vagus nerve, we sought
to determine if these cells also migrate into the liver. Ventral neural tube cells in the caudal hindbrain of chick embryos
were tagged with a replication-deficient retroviral vector containing the LacZ gene on embryonic day 2. Embryos were processed
for detection of labeled cells on embryonic day 5 and 11. Labeled cells were seen in the liver on both days and identified
as hepatocytes. Previously, it was believed that all hepatocytes develop from the gut endoderm. Results of the present study
show an additional source for the formation of liver cells.
Received 25 August 1998; received after revision 5 November 1998; accepted 5 November 1998 相似文献
956.
Kirkpatrick DT 《Cellular and molecular life sciences : CMLS》1999,55(3):437-449
Numerous proteins are involved in the nucleotide excision repair (NER) and DNA mismatch repair (MMR) pathways. The function
and specificity of these proteins during the mitotic cell cycle has been actively investigated, in large part due to the involvement
of these systems in human diseases. In contrast, comparatively little is known about their functioning during meiosis. At
least three repair pathways operate during meiosis in the yeast Saccharomyces cerevisiae to repair mismatches that occur as a consequence of heteroduplex formation in recombination. The first pathway is similar
to the one acting during postreplicative mismatch repair in mitotically dividing cells, while two pathways are responsible
for the repair of large loops during meiosis, using proteins from MMR and NER systems. Some MMR proteins also help prevent
recombination between diverged sequences during meiosis, and act late in recombination to affect the resolution of crossovers.
This review will discuss the current status of DNA mismatch repair and nucleotide excision repair proteins during meiosis,
especially in the yeast S. cerevisiae.
Received 21 September 1998; received after revision 23 November 1998; accepted 23 November 1998 相似文献
957.
MAP kinases in plant signal transduction 总被引:10,自引:0,他引:10
Mitogen-activated protein kinase (MAPK) pathways are modules involved in the transduction of extracellular signals to intracellular
targets in all eukaryotes. Distinct MAPK pathways are regulated by different extracellular stimuli and are implicated in a
wide variety of biological processes. In plants there is evidence for MAPKs playing a role in the signaling of abiotic stresses,
pathogens and plant hormones. The large number and divergence of plant MAPKs indicates that this ancient mechanism of bioinformatics
is extensively used in plants and may provide a new molecular handle on old questions. 相似文献
958.
Wójcik C 《Cellular and molecular life sciences : CMLS》1999,56(11-12):908-917
The proteasome (multicatalytic proteinase complex, prosome) is a major cytoplasmic proteolytic enzyme, responsible for degradation of the vast majority of intracellular proteins. Proteins degraded by the proteasome are usually tagged with multiple ubiquitin moieties, conjugated to the substrates by a complicated cascade of enzymes. Over the last years, evidence has accumulated that changes in the expression and activity of the different components of the ubiquitin-proteasome system occur during apoptosis. Proteasome inhibitors have been used to induce apoptosis in various cell types, whereas in others, these compounds were able to prevent apoptosis induced by different stimuli. The proteasome mediated step(s) in apoptosis is located upstream of mitochondrial changes and caspase activation, and can involve in different systems Bcl-2, Jun N-terminal kinase, heat shock proteins, Myc, p53, polyamines and other factors. 相似文献
959.
Are elicitins cryptograms in plant-Oomycete communications? 总被引:13,自引:0,他引:13
Ponchet M Panabières F Milat M-L Mikes V Montillet JL Suty L Triantaphylides C Tirilly Y Blein JP 《Cellular and molecular life sciences : CMLS》1999,56(11-12):1020-1047
Stimulation of plant natural defenses is an important challenge in phytoprotection prospects. In that context, elicitins, which are small proteins secreted by Phytophthora and Pythium species, have been shown to induce a hypersensitive-like reaction in tobacco plants. Moreover, these plants become resistant to their pathogens, and thus this interaction constitutes an excellent model to investigate the signaling pathways leading to plant resistance. However, most plants are not reactive to elicitins, although they possess the functional signaling pathways involved in tobacco responses to elicitin. The understanding of factors involved in this reactivity is needed to develop agronomic applications. In this review, it is proposed that elicitins could interact with regulating cell wall proteins before they reach the plasma membrane. Consequently, the plant reactivity or nonreactivity status could result from the equilibrium reached during this interaction. The possibility of overexpressing the elicitins directly from genomic DNA in Pichia pastoris allows site-directed mutagenesis experiments and structure/function studies. The recent discovery of the sterol carrier activity of elicitins brings a new insight on their molecular activity. This constitutes a crucial property, since the formation of a sterol-elicitin complex is required to trigger the biological responses of tobacco cells and plants. Only the elicitins loaded with a sterol are able to bind to their plasmalemma receptor, which is assumed to be an allosteric calcium channel. Moreover, Phytophthora and Pythium do not synthesize the sterols required for their growth and their fructification, and elicitins may act as shuttles trapping the sterols from the host plants. Sequence analysis of elicitin genes from several Phytophthora species sheds unexpected light on the phylogenetic relationships among the genus, and suggests that the expression of elicitins is under tight regulatory control. Finally, general involvement of these lipid transfer proteins in the biology of Pythiaceae, and in plant defense responses, is discussed. A possible scheme for the coevolution between Phytophthora and tobacco plants is approached. 相似文献
960.