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31.
The vaccinia virus D4R open reading frame, encoding the essential DNA repair enzyme uracil DNA glycosylase, was expressed in two permanent cell lines, the rabbit kidney cell line RK13 and the human fibroblast cell line 293. The temperature-sensitive vaccinia virus mutant ts4149, which maps within D4R, was able to grow under restrictive conditions in both of these transformed cell lines. Cell clones complemented D4R function to various degrees, demonstrating complementation of an essential vaccinia virus gene by a cell line constitutively expressing the essential function. Thus, the complementing host cells allowed the rescue of a virus defective in the D4R gene, demonstrating that this system may be used for the propagation of defective cytoplasmic DNA viruses. The defective virus grew to high yields only in the engineered cell lines. The data support the hypothesis that early gene products, such as uracil DNA glycosylase, supplied in trans can fully complement essential viral functions.  相似文献   
32.
A force flow relationship based on nonequilibrium thermodynamics was derived to analyze the variable transient state phosphate uptake phenomena of cyanobacteria seen under different growth conditions and external phosphate concentrations. This relationship postulates the following basic properties of the uptake system: First, a threshold value exists, below which incorporation is energetically impossible. Second, threshold values are influenced by the activity of the phosphate uptake system, such that a decrease of the activity increases the threshold level. Third, near the thermodynamic equilibrium the uptake rate is linearly dependent on the free energy of polyphosphate formation and the pH-gradient at the thylakoid membrane. Experiments performed with Anacystis nidulans showed that phosphate uptake characteristics conformed to the properties predicted by the linear force-flow relationship. Linearity extented into regions far form thermodynamic equilibrium, e.g. to high phosphate concentrations, when algae were preconditioned to high phosphate levels. Under phosphate limited growth linearity was confined to a small concentration range, threshold values decreased below 10 nM, and the external concentration approached threshold. The data suggest that the uptake system responds to changes in the external phosphate concentration in the same way as sensory systems to input stimuli by amplifying signals and adapting to them.Abbreviations chl chlorophyll - H e + , H C + , H T + protons in the external medium, the cytoplasmic and thylakoid space respectively - Pc phosphate in the cytoplasmic space - Pe phosphate in the external medium - Pn, Pn+1 polyphosphates - pHT pH-gradient across the thylakoid membrane  相似文献   
33.
P. Strasser  G. Falkner 《Planta》1986,168(3):381-385
The permeability properties of the cell membrane of a symbiotic Nostoc sp. for glutamate and aspartate were investigated. These compounds were translocated across the plasmalemma by a transport system which showed a very high affinity for glutamate and a lower one for aspartate. Since a concomitant release of glutamate was observed during the uptake of these two amino acids it is concluded that the transport proceeds via a counterexchange mechanism. In addition to this counterexchange a net release of glutamate occurred in the dark. Some aspects concerning the possible function of this transport system in the symbiotic association Geosiphon pyriforme are discussed.  相似文献   
34.
Investigations of the energy-dependent accumulation of orthophosphate by the blue-green alga Anacystis nidulans have established: 1. The transport through the cell membrane is the rate-limiting step in the incorporation of phosphate.-2. This transport is facilitated by a carrier that can be activated by Ca2+ and Mg2+ and inhibited by EDTA.-3. The activation of the carrier in the light is associated with changes of the cytoplasmic Mg2+ content.-4. Intracellular phosphate is shown to be present in bound form.-5. The energy-dependent accumulation of orthophosphate within the cell depends strictly on the cytoplasmic pH and not on the energy conversion at the thylakoid membrane which is responsible for the energy supply. The cytoplasmic pH is different in the light, in the dark, and in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). Orthophosphate accumulation can most readily be explained in terms of a pH dependent precipitation into a complex with bivalent cations rather than by an active transport against a concentration gradient.Abbreviation CCCP Carbonyl cyanide m-chlorophenylhydrazone  相似文献   
35.
The forest-bog complex of southeast Alaska   总被引:1,自引:0,他引:1  
Summary Major vegetational, environmental, and peat accumulation patterns were studied in the forest-bog complex of southeast Alaska. Attention was directed to three levels of vegetational pattern: (1) the community type level, with forest, bog, and intermediate types being recognized; (2) the community level, with investigation of major variations within forest, bog, and, to a lesser extent, the intermediate community types; and (3) the subcommunity level, with major patterns of the forest understory and the bog surface, being investigated. Both extensive survey and intensive sampling were carried out in a fairly widespread, but geographically even, array of sites. Chief attention was given to vegetational aspects and gross physical factors, with patterns of these then being used to suggest possible correlating features of habitat. Actual correspondence will be determined in subsequent studies.At the community type level, the three types blended into one another in a continually varying pattern, which, on a gross scale, conformed primarily to surface topography. Forests occurred chiefly on the steep mountain slopes, bogs on land of gentle repose, and intermediate communities on slopes in between these. That the correspondence was with drainage, rather than other microhabitat features related to topography, was shown by forest presence on land of little slope if it were near the ocean or large drainages, or on deep porous substrates, and by bog presence on steep slopes, if any local formations prevented runoff from being rapid the full length of the watershed. Major vegetational patterns on the peats conformed more with peat surface configuration than with peat depth, configuration of underlying topography, or major land slope.Species' patterns at this level included dominance of the upland forests byTsuga heterophylla andPicea sitchensis, withChamaecyparis nootkatensis, Thuja plicata, andTsuga Mertensiana of local importance. The first two species were increasingly sparse, and the last three increasingly conspicuous (within their geographic ranges), in intermediate communities. On the bogs proper, onlyPinus was consistent in occurrence, and the trees were widely scattered, small and slow growing. Major shrub, herbaceous vascular plant, bryophyte and lichen shifts and patterns along this major floristic gradient are described. Some species reached maximum importance in the forests, others in the intermediate type and others in the bogs. The majority of the species had overlapping, but largely independent, patterns of importance.At the community level, two major patterns were suggested by the forest data: (1) a shift from true upland forest, to forest showing increasingly poor drainage, and, finally, to bog forest; and (2) a shift from forests dominated by very large trees, with highPicea importance, an understory largely characterized by scattered small shrubs, herbaceous vascular plants, and mosses and liverworts indicative of moist oxygenated surfaces, to forests with lessPicea, smaller trees, a deep continuous moss cover, dense shrubs where the canopy was somewhat open and only mosses and sparse herbs where the canopy was closed. These patterns are postulated to correspond to specific combinations of slope angle, the possibility of receiving bog drainage waters, nearness to large streams or the ocean, substrate porosity, and varying mixtures of soil fertility, moisture, oxygenation, and depth.The two major patterns suggested for the bogs at the community level are: (1) a gradation from probably soligenous bogs to probably ombrogenous bogs; and (2) a gradation from actively growing bogs of various surface configurations to bogs with an apparently stagnant main surface. Possible recent rejuvenation of a few of these stagnant bogs was indicated. Various possible relationships among the bogs are discussed.The forest subcommunities were subjectively divided into those of (1) varying dominance by different life forms; and (2) variations in surface moisture conditions. Bog surface subcommunities were divided into (1) wet sites, including steep-sided pit ponds, shallow wet hollows, surface drainage systems, floating mats and eroding bare peats; and (2) dry subcommunities, including mounds, varyingSphagnum dominance, and varying importance of bog shrubs and the sedges.The postulated patterns at all levels are based on fairly extreme examples. Many groupings were found that exhibited varying mixtures of these more extreme conditions, either throughout simple communities, or as parts of complex communities. Whether the more extreme conditions are sufficiently numerous and distinct in the region to form a basis of classification, or whether no such limits can be set except by arbitrary decision, and the regional vegetation would be dealt with best on the basis of continuous variation, remains to be determined.The most pronounced impression gained from this vegetation is one of a continuous shifting of habitat patterns and species' occurrence, co-occurrence, and vigor at all levels in both time and space. Such has certainly been observed before with respect to vegetation, but may be particularly conspicuous in this region in which extensive land use and settlement has not occurred; and climate, topography and related features, and peat accumulation are such that a continuous tension exists at all levels between: (1) tendencies for better drainage, forest development, and raised bog humification; and (2) poorer drainage, bog development and raised bog growth. The actual vegetation at any one time and place would depend on the particular combination of the climate and surface physical features at that time and place, and the time lag of vegetational and substrate response to climatic fluctuation.
Résumé Cette étude porte sur les arrangements principaux de végétation, de milieu et d'accumulation de tourbe dans le complexe formé par la forêt et les marais dans l'Alaska du Sud-Est. Notre attention s'est portée sur trois plans de disposition de la végétation: 1) le plan de la communauté forestière, qui comprend la forêt, le marais et des types intermédiaires; 2) le plan de la sous-communauté forestière, qui comprend l'investigation des variations principales dans la forêt, le marais, et, à un moindre degré, les types intermédiaires de la communauté forestière; et 3) le plan de la sous-communauté, qui comprend l'investigation des arrangements principaux du sous-sol forestier et de la surface marécageuse. Nous avons effectué une inspection poussée et fait des prélèvements intenses sur des lieux assez étendus, mais géographiquement unis. On a porté une attention particulière aux aspects de la végétation et aux traits physiques les plus saillants, en se servant de ceux-ci pour découvrir les facteurs possibles de corrélations d'habitat. Des études qui suivent permettront d'en déterminer la corrélation.Au plan de la communauté, les trois genres s'entremêlaient dans un arrangement qui variait continuellement, lequel, en gros, se conformait à la topographie de la surface. On trouvait les forêts surtout sur les pentes raides montagneuses, les marais sur des terres aux lignes douces, et des communautés intermédiaires entre les deux, sur les pentes. La correspondance était avec le drainage plutôt qu'avec d'autres traits microhabitats rattachés à la topographie, et cela était démontré par la présence de forêts sur un terrain peu incliné, dans le cas de la proximité de l'océan, ou de vastes drainages, ou sur de profonds substrates poreux, et par la presénce de marais sur des pentes abruptes quand des formations locales empêchaient l'écoulement rapide tout au long de la ligne de partage des eaux. Les dispositions principales de la végétation sur les tourbières étaient en conformité avec la configuration de la tourbe dans sa surface plus que dans sa profondeur, la configuration de la topographie sous-jacente, ou la majeure inclinaison de terrain.Les arrangements des espèces à ce niveau comprenaient la prédominance des forêts de montagnes avecTsuga heterophylla etPicea sitchensis, avecChamaecyparis nootkatensis, Thuja plicata etTsuga Mertensiana d'importance locale. Les deux premières espèces étaient de plus en plus en évidence (en leur zone géographique) dans les communautés intermédiaires. Sur les marécages mêmes, lePinus seul se trouvait de façon constante, avec des arbres répartis sur une grande étendue, arbres courts et à croissance lente. Pour les principaux arbrisseaux, plantes vasculaires herbacées, bryophytes et lichens, les changements et l'organisation dans le sens de cette gradation de la flore sont décrits. Quelques espèces atteignaient le maximum de leur importance dans les forêts, d'autres dans les formes intermédiaires, d'autres dans les marais. La majorité des espèces montrait un chevauchement dans l'importance de leurs repartitions mais celles-ci étaient hautement indepéndantes.Au niveau de la communauté forestière deux arrangements principaux étaient suggérés par les données de la forêt: 1) une modification depuis la véritable forêt de montagne en forêt de moins en moins drainée et finalement, en forêt marécageuse; 2) une modification à partir de forêts dominées par de gros arbres (surtoutPicea) un sous-sol fortement caractérisé par des arbrisseaux petits et clairsemés, des plantes herbacées vasculaires, desBryophytes etHépatiques, signes de surfaces humides oxygenées; en forêts ayant de moins en moins dePicea, des arbres plus petits, une étendue de mousse profonde et continue, des arbustes abondants là où la voùte s'entouvait quelque peu, et seulement des mousses et des herbes clairsemées là où la voùte d'arbres se refermait.On considère comme admis que ces arrangements correspondent à des combinations de l'inclinaison du terrain à la reception possible d'eaux d'écoulement des marais, à la proximité de grandes rivières ou de l'océan, à la porosité du substratum, et aux combinaisons variées de fertilité du sol, humidité, oxygénation et profondeur. Les deux arrangements principaux supposés pour le marais sur le plan communautaire sont: 1) une gradation depuis les marais produits par des eaux de surface jusqu'aux marais causés par les pluies, et 2) une gradation depuis les marais à poussée active et à configurations de surface variées jusqu'aux marais offrant une surface principale d'apparence stagnante.La division subjective des sous-communautés forestières à la surface des marais, se divisaient en: 1) lieux humides, y compris les étangs à flancs escarpés, trous humides peu profonds, systèmes de drainage de surface, végétaux flottants et tourbes dénudées en décomposition; et 2) sous communautés sèches comprenant des monticules, prédominance diverse deSphagnum, une répartition variée d'arbrisseaux de marécages, et les laîches.Sur tous les plans, les arrangements présumés sont basés sur des exemples presque extrêmes. On a trouvé de nombreaux groupements montrant des mélanges variés de ces conditions les plus extrêmes, soit dans de simples communautés soit comme composants des communautés complexes. Il reste a déterminer si les conditions les plus extrêmes sont suffisamment fréquentes et distinctes dans la région pour donner une base de classification, ou s'il est impossible de poser ces limites, sauf par une décision arbitraire, et serait-il préférable de traiter de la végétation régionale sur la base de la variation continue. Cette végétation donne une forte impression de déplacement continu d'arrangement d'habitat et de co-occurrence d'espèces et de vigueur sur tous les plans à la fois dans le temps et dans l'espace. C'est ce que l'on a déjà observé en ce qui concerne la végétation, mais c'est particulièrement évident dans cette région qui n'a pas connu d'intense utilisation du sol et de colonisation; le climat, la topographie et les caractéristiques qui s'y rattachent aussi bien que l'accumulation de tourbe sont telles qu'une tension persistente existe à tous les niveaux entre: 1) les tendances vers un meilleur drainage, le développement forestier et la transformation en humus des marais elevés et 2) l'insuffisance de drainage, le développement des marécages et l'extension des marécages elevés.


This work was partially supported by the National Science Foundation, Grant Nos. G-2356a, GB-961, and GB-3503.  相似文献   
36.
At least six DNA helicases have been identified during fractionation of extracts from the yeastSaccharomyces cerevisiae. Three of those, DNA helicases B, C, and D, have been further purified and characterized. DNA helicases B and C co-purified with DNA polymerse δ through several chromatographic steps, but were separated from the polymerase by hydrophobic chromatography. DNA helicase D co-purified with Replication Factor C over seven chromatographic steps, and was only separated from it by glycerol gradient centrifugation in the presence of 0.2 M NaCl. All three helicases are DNA dependent ATPases with Km values for ATP of 190 μM, 325 μM, and 60 μM for DNA helicases B, C, and D, respectively. Their DNA helicase activities are comparable. They are 5′–3′ helicases and have pH optima of 6.5–7 and Mg2+ optima of 1–2 mM. However, they differ in the nucleotide requirement for helicase action. Whereas all three helicases preferred ATP, dATP, UTP, CTP, and dCTP as cofactors, DNA helicase C also used GTP, but not dTTP. On the other hand, DNA helicase D used dTTP, but not GTP, and DNA helicase B used neither nucleotide as cofactor. These studies allowed us to conclude that DNA helicases B, C, and D are not only distinct enzymes, but also different from two previously identified yeast DNA helicases, the RAD3 protein and ATPase III.  相似文献   
37.
Responsiveness to a soluble crude Candida albicans antigen (CaAg) by a long-term human lymphoid cell line with B-cell characteristics (PGLC-33H) is demonstrated by the direct migration inhibition (DMI) assay. An inability to detect comparable CaAg responses in other tested B- and T-lymphoid cell lines suggests that this may be a specific response for PGLC-33H cells. CaAg responsiveness is completely abrogated by trypsinization of cells. Regeneration of CaAg responsiveness is temperature dependent, detectable in 8–14 hr in cells maintained at 37°C. Trypsinized cells kept at 4°C do not regain CaAg response. The rate of cell-CaAg interaction is rapid and not temperature dependent. Cells pulsed with CaAg at 37, 25, and 4°C demonstrate comparable DMI responses following a 2-min pulse with CaAg. These findings suggest that PGLC-33H cells have surface receptors for CaAg which result in the inhibition of cell migration upon exposure to antigen.  相似文献   
38.
Present methods are unsatisfactory, for unless an individual infant is widely deviant no satisfactory assessment can be made. Application of various methods to the perinatal period and possible new approaches will be discussed. There is a great need for useful estimates of maturity in this area of growth.  相似文献   
39.
In the clinical setting, mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene enhance the inflammatory response in the lung to Pseudomonas aeruginosa (P. aeruginosa) infection. However, studies on human airway epithelial cells in vitro have produced conflicting results regarding the effect of mutations in CFTR on the inflammatory response to P. aeruginosa, and there are no comprehensive studies evaluating the effect of P. aeruginosa on the inflammatory response in airway epithelial cells with the ΔF508/ΔF508 genotype and their matched CF cell line rescued with wild-type (wt)-CFTR. CFBE41o- cells (ΔF508/ΔF508) and CFBE41o- cells complemented with wt-CFTR (CFBE-wt-CFTR) have been used extensively as an experimental model to study CF. Thus the goal of this study was to examine the effect of P. aeruginosa on gene expression and cytokine/chemokine production in this pair of cells. P. aeruginosa elicited a more robust increase in cytokine and chemokine expression (e.g., IL-8, CXCL1, CXCL2 and TNF-α) in CFBE-wt-CFTR cells compared with CFBE-ΔF508-CFTR cells. These results demonstrate that CFBE41o- cells complemented with wt-CFTR mount a more robust inflammatory response to P. aeruginosa than CFBE41o-ΔF508/ΔF508-CFTR cells. Taken together with other published studies, our data demonstrate that there is no compelling evidence to support the view that mutations in CFTR induce a hyperinflammatory response in human airway epithelial cells in vivo. Although the lungs of patients with CF have abundant levels of proinflammatory cytokines and chemokines, because the lung is populated by immune cells and epithelial cells there is no way to know, a priori, whether airway epithelial cells in the CF lung in vivo are hyperinflammatory in response to P. aeruginosa compared with non-CF lung epithelial cells. Thus studies on human airway epithelial cell lines and primary cells in vitro that propose to examine the effect of mutations in CFTR on the inflammatory response to P. aeruginosa have uncertain clinical significance with regard to CF.  相似文献   
40.
Human cytomegalovirus (HCMV) is a common infection, opportunistically causing disease in people with immune system deficits. HCMV expresses several proteins that contribute to avoidance of the host immune response. The US3 gene is one of the first immune evasion genes expressed following infection. Expression of the US3 gene is highly regulated, with the gene encoding autoregulatory proteins. The largest of the US3 proteins, a 22 kDa resident endoplasmic reticulum protein, binds to MHC class I heavy chain complexes and components of the peptide loading complex, delaying the maturation of the MHC class I complexes and presentation of viral antigen on the surface of infected cells. A smaller US3 protein, a 17 kDa US3 protein, competes with the 22 kDa for protein interactions, counteracting, in part, the effects of the larger protein. The US3 amino acid sequence is highly conserved among clinical isolates and laboratory strains, suggesting an important role for this gene in natural infections in the human host.  相似文献   
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