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71.
Prohibitin, an evolutionarily conserved intracellular protein that blocks DNA synthesis in normal fibroblasts and HeLa cells. 总被引:21,自引:7,他引:14
M J Nuell D A Stewart L Walker V Friedman C M Wood G A Owens J R Smith E L Schneider R Dell' Orco C K Lumpkin et al. 《Molecular and cellular biology》1991,11(3):1372-1381
Genes that act inside the cell to negatively regulate proliferation are of great interest because of their implications for such processes as development and cancer, but these genes have been difficult to clone. This report details the cloning and analysis of cDNA for prohibitin, a novel mammalian antiproliferative protein. Microinjection of synthetic prohibitin mRNA blocks entry into S phase in both normal fibroblasts and HeLa cells. Microinjection of an antisense oligonucleotide stimulates entry into S phase. By sequence comparison, the prohibitin gene appears to be the mammalian analog of Cc, a Drosophila gene that is vital for normal development. 相似文献
72.
Bruce A. McPheron Clive D. Jorgensen Stewart H. Berlocher 《Entomologia Experimentalis et Applicata》1988,46(2):155-160
The apple maggot fly, Rhagoletis pomonella (Walsh), has only recently been found in Utah infesting sour cherry, Prunus cerasus L. An electrophoretic comparison of flies from Utah cherries with flies from Illinois hawthorns, Crataegus mollis (T. & G.) Scheele (a native host within the native range of the fly), show a marked reduction of genetic variability in the Utah sample. This result is indicative of a genetic bottleneck associated with the establishment of the apple maggot population in Utah cherries.
Résumé R. pomonella (Walsh), est originaire de Crataegus dans l'Amérique du N.E. Il attaque de nombreux autres fruits, y compris les pommes et les cerises aigres (Prunus cerasus). La mouche a été récemment signalée en Utah, à la fois sur cerises et sur Crataegus douglasii. Nous avons comparé les niveaux de variabilité génétique d'une population de l'Utah contaminant les cerises et d'une population de l'Illinois contaminant C. mollis (la population de l'Illinois est représentative des niveaux de variabilité génétique dans l'aire d'origine de la mouche).La variabilité génétique à 17 loci a été évaluée par électrophorèse sur gel d'amidon. 10 de ces loci sont polymorphes dans la population d'Illinois, mais seulement 4 dans la population de l'Utah. Les fréquences alléliques de ces 4 loci de R. pomonella diffèrent significativement en Utah et en Illinois. La population de l'Utah présente nettement moins d'allèles par locus, un plus faible pourcentage de loci polymorphes et une hétérozygotie moyenne plus faible que la population de l'Illinois. Tous ces résultats sont conformes aux conséquences prévisibles d'un goulot d'étranglement.Deux explications existent pour cette perte de variabilité, toutes les deux liées à la combinaison de la faible taille de la population et de la dérive génétique ultérieure. Pour la première, la colonisation du cerisier par les mouches venant de Crataegus peut avoir provoqué un goulot d'étranglement génétique. Au contraire, la réduction de la variabilité peut avoir été la conséquence de la colonisation de l'Utah par R. pomonella. Nous retenons cette dernière comme la cause la plus vraisemblable de la variabilité génétique de la population de R. pomonella contaminant les cerises de l'Utah.相似文献
73.
J V Lebesque A A Hart F A Stewart 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1988,53(3):417-428
The tolerance of a late-responding tissue to reirradiation after long time intervals has been analysed using the F-type tissue model. In this model the tissue is composed of identical cells, each of which is capable of extensive proliferation and of tissue-specific function. The model was adapted to calculate the response to two fractions of radiation given in a variable overall time. For two equal doses of radiation the repair of tissue damage after the first fraction could be detected theoretically by a change in the rate of cell depletion after retreatment and by an increase in the minimum cell number attained. For an 'experimental set-up', in which a constant first dose was followed by a range of retreatment doses in a variable overall time, the repair of tissue damage theoretically could be detected most sensitively by a shift of the dose-response curves to higher retreatment doses as the time interval between the two doses was increased. A prerequisite for a proper comparison of these dose-response curves was that the responses were evaluated at times after the first dose determined by the minimal latency times after high retreatment doses. From a comparison of these theoretical results with experimental findings for mouse kidneys it was concluded that no recovery of tissue function took place over a 6-month period. Instead it appeared that the kidneys had become more sensitive to irradiation over this period. 相似文献
74.
N-terminal half of CheB is involved in methylesterase response to negative chemotactic stimuli in Escherichia coli. 总被引:3,自引:1,他引:2
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The chemotactic receptor-transducer proteins of Escherichia coli are responsible for directing the swimming behavior of cells by signaling for either straight swimming or tumbling in response to chemostimuli. The signaling states of these proteins are affected not only by the concentrations of various stimuli but also by the extent to which they have been methylated at specific glutamyl residues. The activities of a chemotaxis-specific methyltransferase (CheR) and a chemotaxis-specific methylesterase (CheB) are regulated in response to chemotactic stimuli to enable sensory adaptation to unchanging levels of stimuli by appropriately shifting the signaling states of the transducer proteins. For CheB this regulation involves a feedback loop that requires some of the components making up the chemotactic signal transduction machinery of the cell. This feedback loop causes the methylesterase activity of CheB to decrease transiently in response to attractant stimuli and to increase transiently in response to negative stimuli (repellent addition or attractant removal). In this report we demonstrate that the methylesterase response to negative stimuli involves the N-terminal half of the CheB protein, whereas the response to positive stimuli does not require this segment of the protein. Both aspects of the methylesterase response to positive stimuli does not require this segment of the protein. Both aspects of the methylesterase response require CheA. In addition, we demonstrate that mutant forms of CheB lacking methylesterase activity can adversely affect the swimming behavior and chemotactic ability of cells and can markedly diminish modulation of the wild-type methylesterase activity in response to negative stimuli. The significance of these results is discussed in relation to the recent demonstration of phosphoryl transfer from CheA to CheB (J. F. Hess, K. Oosawa, N. Kaplan, and M. I. Simon, Cell 53:79-87, 1988) and the discovery of sequence homology between the N-terminal half of CheB and CheY (A. Stock, D. E. Koshland, Jr., and J. Stock, Proc. Natl. Acad. Sci. USA 82:7989-7993, 1985). 相似文献
75.
Product inhibition of immobilized Escherichia coli arising from mass transfer limitation. 总被引:3,自引:3,他引:0
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Mass transfer-limited removal of metabolic products led to product-inhibited growth of Escherichia coli that was immobilized in a model system. Comparison of the growth kinetics of immobilized and free-living cells revealed no further physiological differences between cells in these two modes of existence beyond those manifested in the local concentrations of substrate and product. Bacteria were retained on a microporous membrane in a dense, planar aggregate and were grown anaerobically on a glucose-based minimal medium. Radioisotope labeling of the immobilized cell mass with 35S was used to determine growth kinetic parameters. Growth rates in the immobilized cell layer were measured by an autoradiographic technique which allowed comparison of the size of the growing region with the rate of cell convection caused by growth. Immobilized cell growth rates and growth yields ranged from near maximal (0.56 h-1 and 39 g of dry cell weight/mol of glucose, respectively) to substantially reduced (0.15 h-1 and 15 g/mol). The depression of these kinetic parameters was attributed to product inhibition arising from mass transfer-limited removal of acidic waste products from the cell mass. A simple one-dimensional reaction-diffusion model, which incorporated data on the product-inhibited growth kinetics of free-living cells collected in a product-limited chemostat, satisfactorily predicted product inhibition of immobilized cell growth. 相似文献
76.
Kinetic measurements of fusion of phosphatidylserine-containing vesicles by electron microscopy and fluorometry 总被引:1,自引:0,他引:1
Large unilamellar vesicles (REV) containing phosphatidylserine and phosphatidylethanolamine at a ratio of 1:3 were induced to fuse by adding calcium (4 mM). The kinetics of fusion was monitored by fluorometry using terbium or dipicolinic acid-containing vesicles. The morphology and the states of vesicle aggregation and fusion were examined at approx. 2, 30, 60, 150 and 900 s after calcium addition, by rapid quenching and freeze-fracture electron microscopy. The size and the state of aggregation of vesicles are quantitated from 4000 randomly selected vesicles. The aggregation and fusion kinetics as assayed by fluorescence volume mixing is very well simulated and predicted by the mass action model. The model essentially predicts the time course of the distribution of the aggregates and the increase in size of fused particles as measured by electron microscopy, although in some cases the predicted fusion rate exceeds that by morphometric measurement. No morphological features can be defined as fusion intermediates, although bead-like and rim-like materials may be attributed to the remnants of broken diaphragms between fusion partners. 相似文献
77.
Synthesis and characterization of deoxy analogues of diphytanylglycerol phospholipids 总被引:1,自引:0,他引:1
Novel analogues of diphytanyl phospholipids, 2,3-diphytanyl sn-1-glycerol-1-phosphoryl-1'-(1',3'-propanediol) (dPG), 2,3-diphytanyl-sn-glycerol-1-phosphoryl-1'-propanol (ddPG) and 2,3-diphytanyl-sn-glycerol-1-phosphoryl-1'-(1',3'-propanediol-3'-p hosphate) (dPGP), were synthesized according to modifications of previously published procedures. The samples were TLC and analytically pure and were characterized by 13C- and 1H-NMR and negative FAB/MS. The pK values of dPGP in aqueous dispersions or in methanol/water (1:1, v/v) were determined by potentiometric titration and compared with those of 2,3-diphytanyl-sn-glycerol-1-phosphoryl-3'-sn-glycerol-1'-phosphat e (PGP). The dissociation constant of the third ionizable POH group of dPGP was more than 2 pK units higher than that of PGP, indicating that the free glycerol hydroxyl group plays an important role in headgroup conformation and stabilization, perhaps through hydrogen bonding with the phosphate group(s). 相似文献
78.
Tropomyosin from equine platelets was reacted with N-(1-pyrenyl)iodoacetamide, a sulfhydryl-specific fluorescent reagent, to give an average extent of incorporation of 1.12 pyrene (Py) groups per platelet tropomyosin (P-TM) chain. The predominant site of reaction on P-TM was the penultimate COOH-terminal residue, Cys-246. The high proportion of the total emission that is due to pyrene ecximers and the pretransition observed in thermal denaturation of Py-P-TM point to a rather loose structure for the COOH-terminal amino acid residues of P-TM. The label on Cys-246 also reports on end-to-end overlap interactions that occur between two different tropomyosin molecules. Additions to a Py-P-TM solution at low ionic strength of unlabeled P-TM, rabbit cardiac tropomyosin (C-TM), or a carboxypeptidase A treated, nonpolymerizable derivative of C-TM all reduce the extent of excimer fluorescence from the sample. Addition of salt greatly reduces the effects of the unlabeled TM species on the Py-P-TM emission spectrum. Circular dichroism measurements indicate Py-P-TM still to be greater than 95% helical. However, analysis of excimer fluorescence levels in samples that contained a constant protein concentration but different mole ratios of labeled to unlabeled P-TM suggests that the bulky pyrene group may diminish the tendency of Py-P-TM to polymerize in an end-to-end manner. 相似文献
79.
Effects of KCN and Salicylhydroxamic Acid on Respiration of Soybean Leaves at Different Ages 总被引:5,自引:5,他引:0
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Measurements of respiration were made on leaf discs from glasshouse-grown soybean (Glycine max [L.] Merr. cv `Corsoy') plants in the presence and absence of cyanide (KCN) and salicylhydroxamic acid (SHAM). O2 uptake by mature leaves measured at 25°C was stimulated by 1 millimolar KCN (63%) and also by 5 millimolar azide (79%). SHAM, an inhibitor of the alternative oxidase and a selection of other enzymes, also stimulated O2 uptake by itself at concentration of 10 millimolar. However, in combination, KCN and SHAM were inhibitory. The rate of O2 uptake declined consistently with leaf age. The stimulation of O2 uptake by KCN and by SHAM occurred only after a certain stage of leaf development had been reached and was more pronounced in fully expanded leaves. In young leaves, O2 uptake was inhibited by both KCN and SHAM individually. The uncoupler, p-trifluoromethoxy carbonylcyanide phenylhydrazone, stimulated leaf respiration at all ages studied, the stimulation being more pronounced in fully expanded leaves. The uncoupled rate was inhibited by KCN and SHAM individually. The capacity of the cytochrome path declined with leaf age, paralleling the decline in total respiration. However, the capacity of the alternative path peaked at about full leaf expansion, exceeding the cytochrome capacity and remaining relatively constant. These results are consistent with the presence in soybean leaves of an alternative path capacity that seems to increase with age, and they suggest that the stimulation of O2 uptake by KCN and NaN3 in mature leaves was mainly by the SHAM-sensitive alternative path. The stimulation of O2 uptake by SHAM was not expected, and the reason for it is not clear. 相似文献
80.
Continuous and batch cultures of marine sulphate-reducing bacteria (SRB) in North Sea water were irradiated with 110000 to 329500 μWs/cm2 of ultraviolet radiation (wavelength 253.7 nm) with a commercial u.v. sterilizing unit. A 100% kill was obtained with logarithmic cultures of Desulfovibrio desulfuricans NCIMB 8400 at population densities of 10–104 /ml. A >99.99% kill was obtained with a mixture (ca 105 /ml) of batch grown Desulfovibrio spp. and oilfield SRB enrichments. Ultraviolet irradiation was less effective against the indigenous heterotrophic bacteria in the seawater ( ca 90% kill). 相似文献