共查询到20条相似文献,搜索用时 31 毫秒
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Stacy A. Anderson Manasa B. Satyanarayan Ryan L. Wessendorf Yan Lu Donna E. Fernandez 《The Plant cell》2021,33(8):2812
The chloroplasts and mitochondria of photosynthetic eukaryotes contain proteins that are closely related to cytosolic Guided Entry of Tail-anchored proteins3 (Get3). Get3 is a targeting factor that efficiently escorts tail-anchored (TA) proteins to the ER. Because other components of the cytosolic-targeting pathway appear to be absent in organelles, previous investigators have asserted that organellar Get3 homologs are unlikely to act as targeting factors. However, we show here both that the Arabidopsis thaliana chloroplast homolog designated as GET3B is structurally similar to cytosolic Get3 proteins and that it selectively binds a thylakoid-localized TA protein. Based on genetic interactions between a get3b mutation and mutations affecting the chloroplast signal recognition particle-targeting pathway, as well as changes in the abundance of photosynthesis-related proteins in mutant plants, we propose that GET3B acts primarily to direct proteins to the thylakoids. Furthermore, through molecular complementation experiments, we show that function of GET3B depends on its ability to hydrolyze ATP, and this is consistent with action as a targeting factor. We propose that GET3B and related organellar Get3 homologs play a role that is analogous to that of cytosolic Get3 proteins, and that GET3B acts as a targeting factor in the chloroplast stroma to deliver TA proteins in a membrane-specific manner.A chloroplast homolog of a cytosolic protein involved in posttranslational targeting of proteins to the ER is a targeting factor in chloroplasts that directs proteins to the thylakoids. 相似文献
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紫色杆菌CV31532中群体感应系统产生的信号分子C6-HSL是由cviI基因编码合成的。在限氮条件下,以D-葡萄糖酸钠、果糖、葡萄糖为唯一碳源时,紫色杆菌CV31532均产生聚-3-羟基丁酸,且以D-葡萄糖酸钠为唯一碳源时积累量最高。利用气相色谱分析发现,紫色杆菌CV31532培养48 h的PHA积累量显著高于其群体感应合成酶突变株CV026 PHA的积累量;通过薄层层析分析发现紫色杆菌CV31532合成信号分子的量在48 h显著提高;外源添加C6-HSL信号分子可显著提高突变体CV026 PHA的积累量。由此推测,紫色杆菌群体感应系统参与调控胞内PHA的合成。 相似文献
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Patterson KR Remmers C Fu Y Brooker S Kanaan NM Vana L Ward S Reyes JF Philibert K Glucksman MJ Binder LI 《The Journal of biological chemistry》2011,286(26):23063-23076
Neurofibrillary tangles, composed of insoluble aggregates of the microtubule-associated protein Tau, are a pathological hallmark of Alzheimer disease (AD) and other tauopathies. However, recent evidence indicates that neuronal dysfunction precedes the formation of these insoluble fibrillar deposits, suggesting that earlier prefibrillar Tau aggregates may be neurotoxic. To determine the composition of these aggregates, we have employed a photochemical cross-linking technique to examine intermolecular interactions of full-length Tau in vitro. Using this method, we demonstrate that dimerization is an early event in the Tau aggregation process and that these dimers self-associate to form larger oligomeric aggregates. Moreover, using these stabilized Tau aggregates as immunogens, we generated a monoclonal antibody that selectively recognizes Tau dimers and higher order oligomeric aggregates but shows little reactivity to Tau filaments in vitro. Immunostaining indicates that these dimers/oligomers are markedly elevated in AD, appearing in early pathological inclusions such as neuropil threads and pretangle neurons as well as colocalizing with other early markers of Tau pathogenesis. Taken as a whole, the work presented herein demonstrates the existence of alternative Tau aggregates that precede formation of fibrillar Tau pathologies and raises the possibility that these hierarchical oligomeric forms of Tau may contribute to neurodegeneration. 相似文献
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The effects of 17 beta-estradiol (E2) on sperm-egg interactions in the mouse were investigated. It was shown that E2 induces adhesiveness of the sperm head, expressed as sperm-sperm and sperm-egg binding. Since the concentration dependence of this process was similar to that observed for stimulation of in vitro fertilization by E2, it is suggested that induction of adhesiveness or initiation of processes that cause adhesiveness of the sperm head are of biological significance as preparatory steps for fertilization. Finally, the content of E2 in mouse eggs was determined and found to be 0.2 pg/egg, equally distributed between the oocyte together with the zona pellucida and the follicular cells with their associated intercellular matrix. The intra-ovum concentration is estimated as 10(-6) M. 相似文献
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Fischer RA 《Plant physiology》1971,47(4):555-558
With isolated epidermal strips of Vicia faba, the intensity of potassium-staining in the guard cells of stomata was calibrated against the uptake of radioactively labeled potassium. By using this calibration, the quantity of potassium that had accumulated in the guard cells, as stomata of leaves of Vicia open in the light, was estimated. Results support the hypothesis that in leaves, as well as in isolated epidermal strips, potassium and an accompanying anion comprise the major, osmotically active solutes in the guard cells of open stomata. 相似文献
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Roy W. Keenan Michael Kruczek Lynn Fusinato 《Archives of biochemistry and biophysics》1975,167(2):697-705
Cell-free preparations from Tetrahymena pyriformis catalyze the incorporation of glucose from UDP-glucose into a glucolipid having properties which are identical to those of other dolichyl phosphoryl sugar derivatives. Kinetic and other experiments have provided evidence that this glucolipid serves as glucose donor for two other types of glucosylated substances, one of which has been tentatively identified as an oligosaccharide lipid and the other a glycoprotein or glycoproteins. In addition, the partially purified glucolipid served as a glucosyl donor to these cell components, suggesting that in this protozoan, at least part of the glycoprotein is synthesized by reactions involving lipid-linked sugars in a manner analogous to that which has been observed in glycoprotein synthesis in mammalian cells. 相似文献
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Maximum photobioreactor (PBR) efficiency is a must in applications such as the obtention of microalgae-derived fuels. Improving PBR performance requires a better understanding of the "light regime", the varying irradiance that microalgal cells moving in a dense culture are exposed to. We propose a definition of light regime that can be used consistently to describe the continuously varying light patterns in PBRs as well as in light/dark cycles. Equivalent continuous and light/dark regimes have been experimentally compared and the results show that continuous variations are not well represented by light/dark cycles, as had been widely accepted. It has been shown that a correct light regime allows obtaining photosynthetic rates higher than the corresponding to continuous light, the so-called "flashing light effect" and that this is possible in commercial PBRs. A correct PBR operation could result in photosynthetic efficiency close to the optimum eight quanta per O(2). 相似文献
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Duggan J Jamal G Tilley M Davis B McKenzie G Vere K Somekh MG O'Shea P Harris H 《European biophysics journal : EBJ》2008,37(8):1279-1289
The presence of microdomains or rafts within cell membranes is a topic of intense study and debate. The role of these structures
in cell physiology, however, is also not yet fully understood with many outstanding problems. This problem is partly based
on the small size of raft structures that presents significant problems to their in vivo study, i.e., within live cell membranes.
But the structure and dynamics as well as the factors that control the assembly and disassembly of rafts are also of major
interest. In this review we outline some of the problems that the study of rafts in cell membranes present as well as describing
some views of what are considered the generalised functions of membrane rafts. We point to the possibility that there may
be several different ‘types’ of membrane raft in cell membranes and consider the factors that affect raft assembly and disassembly,
particularly, as some researchers suggest that the lifetimes of rafts in cell membranes may be sub-second. We attempt to review
some of the methods that offer the ability to interrogate rafts directly as well as describing factors that appear to affect
their functionality. The former include both near-field and far-field optical approaches as well as scanning probe techniques.
Some of the advantages and disadvantages of these techniques are outlined. Finally, we describe our own views of raft functionality
and properties, particularly, concerning the membrane dipole potential, and describe briefly some of the imaging strategies
we have developed for their study. 相似文献
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Characteristics of electrical signals in poplar and responses in photosynthesis 总被引:1,自引:0,他引:1
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To gain an understanding of the role of electrical signaling in trees, poplar (Populus trichocarpa, Populus tremula x P. tremuloides) shoots were stimulated by chilling as well as flaming. Two kinds of signal propagation were detected by microelectrode measurements (aphid technique) in the phloem of leaf veins: (1) basipetal, short-distance signaling that led to rapid membrane hyperpolarization caused by K+-efflux within the leaf lamina; and (2) acropetal, long-distance signaling that triggered depolarization of the membrane potential in the leaf phloem. In the latter, the depolarizing signals travel across the stem from the manipulated leaves to adjacent leaves where the net CO2 uptake rate is temporarily depressed toward compensation. With regard to photosystem II, both heat-induced long-distance and short-distance signaling were investigated using two-dimensional "imaging" analysis of chlorophyll fluorescence. Both types of signaling significantly reduced the quantum yield of electron transport through photosystem II. Imaging analysis revealed that the signal that causes yield reduction spreads through the leaf lamina. Coldblocking of the stem proved that the electrical signal transmission via the phloem becomes disrupted, causing the leaf gas exchange to remain unaffected. Calcium-deficient trees showed a marked contrast inasmuch as the amplitude of the electrical signal was distinctly reduced, concomitant with the absence of a significant response in leaf gas exchange upon flame wounding. In summary, the above results led us to conclude that calcium as well as potassium is involved in the propagation of phloem-transmitted electrical signals that evoke specific responses in the photosynthesis of leaves. 相似文献
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Robert Sugden 《Biology & philosophy》2011,26(5):717-736
The paper explores how, in economics and biology, theoretical models are used as explanatory devices. It focuses on a modelling
strategy by which, instead of starting with an unexplained regularity in the world, the modeller begins by creating a credible
model world. The model world exhibits a regularity, induced by a mechanism in that world. The modeller concludes that there
may be a part of the real world in which a similar regularity occurs and that, were that the case, the model would offer an explanation. Little concrete guidance is given about where such a regularity might be found. Three
modelling exercises in evolutionary game theory—one from economics and two from biology—are used as case studies. Two of these
(one from each discipline) exemplify ‘explanation in search of observation’. The third goes a step further, analysing a regularity
in a model world and treating it as informative about the real world, but without saying anything about real phenomena. The
paper argues that if the relation between the model and real worlds is understood in terms of similarity, and if modelling
is understood as an ongoing discovery process rather than as the demonstration of empirical truths, there can be value in
creating explanations before finding the regularities that are to be explained. 相似文献
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SenC, a Sco1 homolog found in the purple photosynthetic bacteria, has been implicated in affecting photosynthesis and respiratory gene expression, as well as assembly of cytochrome c oxidase. In this study, we show that SenC from Rhodobacter capsulatus is involved in the assembly of a fully functional cbb(3)-type cytochrome c oxidase, as revealed by decreased cytochrome c oxidase activity in a senC mutant. We also show that a putative copper-binding site in SenC is required for activity and that a SenC deletion phenotype can be rescued by the addition of exogenous copper to the growth medium. In addition, we demonstrate that a SenC mutation has an indirect effect on gene expression caused by a reduction in cytochrome c oxidase activity. A model is proposed whereby a reduction in cytochrome c oxidase activity impedes the flow of electrons through the respiratory pathway, thereby affecting the oxidation/reduction state of the ubiquinone pool, leading to alterations of photosystem and respiratory gene expression. 相似文献
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It has been reported that Candida albicans can form germ-tubes only in the narrow pH range of 6-8, and that by changing only the pH one can regulate germ-tube formation. We found that the pH minimum for germ-tube formation could be dramatically lowered by eliminating the glucose present in many induction solutions. Lee's medium lacking glucose, ethanol, N-acetyl-D-glucosamine, and proline induced germ-tubes at pH values as low as 3 under most conditions. The presence of as little as 1 mM-glucose in these induction solutions was sufficient to cause the cells to grow either as yeasts with multiple buds or as pseudohyphae when the pH was 3.7. However, when C. albicans was grown in any of the above induction solutions (with the exception of ethanol), containing 200 mM-glucose buffered at pH 5.8, not only were germ-tubes formed, but their rate of formation and length were also increased. Preincubation of the cells in a solution buffered at pH 3.7 and containing 200 mM-glucose, before exposure to induction solutions lacking glucose at pH 3.7 or at pH 5.8, did not inhibit germ-tube formation. Likewise, addition of glucose after 45 min exposure to an induction solution was without effect. Theophylline and dibutyryl cAMP did not counteract the action of glucose. Other sugars which suppressed germ-tube formation at low pH were fructose, galactose, mannose, xylose, gluconic acid and the nonmetabolizable sugar 3-O-methylglucose. These results indicate that pH does not directly regulate dimorphism in C. albicans, and that glucose or its metabolites may play an important role. 相似文献
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Previous work has shown that the carAB operon of Salmonella typhimurium is transcribed from tandem promoters, P1 and P2, that are negatively controlled by pyrimidines and arginine, respectively. The results reported here show that purines also negatively control expression of carAB and that this effect is absent in a purR ::Tn 10 derivative. Primer-extension experiments established that the purine effect is exerted at P1, thus redefining this promoter as sensitive to both purines and pyrimidines. The results of gel-retardation experiments as well as DNase I and premethylation footprintings indicate that the purine repressor interacts with a PUR box 85 bp upstream of P1. Modification of this PUR box by site-directed mutagenesis abolishes the repression by purines in a carA :: lacZ fusion, confirming that this box functions in vivo in purine control of carAB expression. 相似文献
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Fagerström T 《Trends in ecology & evolution》1988,3(11):303-306
Traditional niche theory has its formal roots in the equilibrium solutions to Lotka-Volterra type equations. In recent years, this theory has lost much of its former pre-eminence for those interested in communities of sessile organisms, as witnessed by two recent reviews in TREE. Of the alternative theories that are now emerging, the so-called lottery theories have in common the assumption that the population dynamics of species are partly governed by random factors that are intrinsic to the system. They are thus genuinely stochastic community theories, in that randomness is taken as a system's property rather than as a 'disturbance' that is imposed from the outside. Analyses of these theories suggest, contrary to classical results, that coexistence of very similar species is possible, that environmental variability generally enhances such coexistence and that convergent, rather than divergent, evolution may be a result of interspecific competitive interactions. 相似文献
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Airway remodeling in patients with chronic asthma is characterized by a thickening of the airway walls. It has been demonstrated in previous theoretical models that this change in thickness can have an important mechanical effect on the properties of the wall, in particular on the phenomenon of mucosal folding induced by smooth muscle contraction. In this paper, we present a model for mucosal folding of the airway in the context of growth. The airway is modeled as a bilayered cylindrical tube, with both geometric and material nonlinearities accounted for via the theory of finite elasticity. Growth is incorporated into the model through the theory of morphoelasticity. We explore a range of growth possibilities, allowing for anisotropic growth as well as different growth rates in each layer. Such nonuniform growth, referred to as differential growth, can change the properties of the material beyond geometrical changes through the generation of residual stresses. We demonstrate that differential growth can have a dramatic impact on mucosal folding, in particular on the critical pressure needed to induce folding, the buckling pattern, as well as airway narrowing. We conclude that growth may be an important component in airway remodeling. 相似文献
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Yu. S. Akishev I. V. Kochetov A. I. Loboiko A. P. Napartovich 《Plasma Physics Reports》2002,28(12):1049-1059
Numerical simulations of a negative corona in air demonstrate that the experimentally observed regime of self-oscillations, known as Trichel pulses, is well described by a three-dimensional axisymmetric model that is based on the standard transport equations and in which only the ion-induced secondary electron emission at the cathode is taken into account. The quantitative difference between the measured and calculated values of the mean current and the pulse repetition rate most likely stems from the insufficiently large dimensions of the computation region and from the fact that the point shape adopted in simulations somewhat inexactly conforms to that used in experiments. It was found that the transverse discharge structure near the cathode radically changes during the pulse. Specifically, as the current grows, a cathode sheath forms at the discharge axis and expands over the cathode surface. When the current falls off, the cathode sheath is rapidly destroyed; as a result, the characteristic field structure is well defined only near the discharge axis and becomes virtually indistinguishable as the current decreases by an order of magnitude. 相似文献