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51.
Dominique Duviard 《Insectes Sociaux》1969,16(2):115-133
Résumé La ComposéeVernonia guineensis Benth., abondante dans les savanes préforestières de Côte d'Ivoire, fleurit quelques semaines après le passage des feux de brousse. Plusieurs espèces de Fourmis sont récoltées régulièrement sur la plante: ce sont surtoutCamponotus acvapimensis et unCremastogaster du genreAcroclia.Les Fourmis se nourrissent de sécrétions sucrées qui suintent au niveau des bractées des jeunes capitules, mais pratiquent également l'élevage d'Homoptères.Divers types de constructions sont décrits et, en particulier, les loges édifiées parC. acvapimensis pour abriter un Jassidæ:Selenocephalus sp.L'influence de l'environnement végétal sur la faune myrmécologique exploitantV. guineensis est mise en évidence.
Summary Vernonia guineensis Benth. (Compositæ). common in the forest-savanna mosaic of Ivory Coast, blooms a few weeks after the fires. Several species of Ants are collected then on the forb; especiallyCamponotus acvapimensis and a species ofCremastogaster (Acroclia).These ants feed on seepings from the young flower heads, and search for exsudates of Homopterans.Various buildings are described, particularly shelters made byC. acvapimensis for the leaf—hopperSelenocephalus sp.Influence of botanical environment on the ants exploitingV. guineensis is shown.相似文献
52.
Eva-Marià Kupsch Dominique Aubel Carol P. Gibbs Andreas F. Kahrs Thomas Rudel Thomas F. Meyer 《Molecular & general genetics : MGG》1996,250(5):558-569
A versatile shuttle system has been developed for genetic complementation with cloned genes of transformable and non-transformableNeisseria mutants. By random insertion of a selectable marker into the conjugativeNeisseria plasmidptetM25.2, a site within this plasmid was identified that is compatible with plasmid replication and with conjugative transfer of plasmid. Regions flanking the permissive insertion site of ptetM25.2 were cloned inEscherichia coli and served as a basis for the construction of the Hermes vectors. Hermes vectors are composed of anE. coli replicon that does not support autonomous replication inNeisseria, e.g. ColE1, p15A, orori
fd, fused with a shuttle consisting of a selectable marker and a multiple cloning site flanked by the integration region of ptetM25.2. Complementation of a non-transformableNeisseria strain involves a three-step process: (i) insertion of the desired gene into a Hermes vector; (ii) transformation of Hermes into aNeisseria strain containing ptetM25.2 to create a hybrid ptetM25.2 via gene replacement by the Hermes shuttle cassette; and (iii) conjugative transfer of the hybrid ptetM25.2 into the finalNeisseria recipient. Several applications for the genetic manipulation of pathogenicNeisseriae are described. 相似文献
53.
Dominique Le Grand Michel Solsona Renate Rosengarten francois Poumarat 《FEMS microbiology letters》1996,144(2-3):267-275
Abstract The variability of predominant Mycoplasma bovis surface antigens in the presence of specific immune pressure was analyzed in an in vitro assay to determine if M. bovis could escape immune destruction. We have shown that serum antibodies from immunized or experimentally infected calves and monoclonal antibodies which specifically react with previously characterized or as yet undefined major M. bovis membrane surface proteins cause repression of expression or shortening of the target protein, or induce switching to expression of an antigenically distinct variant protein. We have further demonstrated that removal of the inducing antibody results in reversion to the original phenotype. These results suggest that the level of expression and the length of M. bovis surface antigens in the host is modulated by cognate antibodies. According to the surface antigenic variation systems, random selection of preexisting variants resistant to antibody-mediated inhibition or direct regulation of gene expression may be means by which this organism evades host immune defences. 相似文献
54.
Dominique Rumeau Stephan Cuiné Laurent Fina Nathalie Gault Michel Nicole Gilles Peltier 《Planta》1996,199(1):79-88
The intracellular compartmentation of carbonic anhydrase (CA; EC 4.2.1.1), an enzyme that catalyses the reversible hydration of CO2 to bicarbonate, has been investigated in potato (Solanum tuberosum L.) leaves. Although enzyme activity was mainly located in chloroplasts (87% of total cellular activity), significant activity (13%) was also found in the cytosol. The corresponding CA isoforms were purified either from chloroplasts or crude leaf extracts, respectively. The cytosolic isoenzyme has a molecular mass of 255 000 and is composed of eight identical subunits with an estimated M
r of 30000. The chloroplastic isoenzyme (M
r 220000) is also an octamer composed of two different subunits with M
r estimated at 27 000 and 27 500, respectively. The N-terminal amino acid sequences of both chloroplastic CA subunits demonstrated that they were identical except that the M
r-27 000 subunit was three amino acids shorter than that of the M
r-27 500 subunit. Cytosolic and chloroplastic CA isoenzymes were found to be similarly inhibited by monovalent anions (Cl–, I–, N
3
-
and NO
3
-
) and by sulfonamides (ethoxyzolamide and acetozolamide). Both CA isoforms were found to be dependent on a reducing agent such as cysteine or dithiothreitol in order to retain the catalytic activity, but 2-mercaptoethanol was found to be a potent inhibitor. A polyclonal antibody directed against a synthetic peptide corresponding to the N-terminal amino acid sequence of the chloroplastic CA monomers also recognized the cytosolic CA isoform. This antibody was used for immunocytolocalization experiments which confirmed the intracellular compartmentation of CA: within chloroplasts, CA is restricted to the stroma and appears randomly distributed in the cytosol.Abbreviations BSA
bovine serum albumin
- CA
carbonic anhydrase
- PMSF
phenylmethylsulphonyl fluoride
- BAM
benzamidine
- DTT
dithiothreitol
- 2-ME
2-mercaptoethanol
- PVDF
polyvinylidene difluoride
The authors thanks P. Carrier and Dr. B. Dimon for technical assistance with the mass-spectrometry measurements. 相似文献
55.
Clare Gough Pascale Hemon Maurice Tronchet Christophe Lacomme Yves Marco Dominique Roby 《Molecular genetics and genomics : MGG》1995,247(3):323-337
A family of genes, the so-called msr genes (multiple stimulus response), has recently been identified on the basis of sequence homology in various plant species. Members of this gene family are thought to be regulated by a number of environmental or developmental stimuli, although it is not known whether any one member responds more specifically to one stimulus, or whether each gene member responds to various environmental stimuli. In this report, we address this question by studying the tobacco msr gene str246C. Using transgenic tobacco plants containing 2.1 kb of 5′ flanking DNA sequence from the str246C gene fused to the β-glucuronidase (GUS) coding region, the complex expression pattern of the str246C promoter has been characterized. Expression of the str246C promoter is strongly and rapidly induced by bacterial, fungal and viral infection and this induction is systemic. Elicitor preparations from phytopathogenic bacteria and fungi activate the str246C promoter to high levels, as do wounding, the application of auxin, auxin and cytokinin, salicylic acid or copper sulfate, indicating the absence of gene specialization within the msr gene family, at least for str246C. In addition, GUS activity was visualized. histochemically in root meristematic tissues of tobacco seedlings and is restricted to roots and sepals of mature plants. Finally, analysis of a series of 5′ deletions of the str246C promoter-GUS gene fusion in transgenic tobacco plants confirms the involvement of multiple regulatory elements. A region of 83 by was found to be necessary for induction of promoter activity in response to Pseudomonas solanacearum, while auxin inducibility and root expression are apparently not controlled by this element, since its removal does not abolish either response. An element of the promoter with a negative effect on promoter activation by P. solanacearum was also identified. 相似文献
56.
Eric Dufour Paul Robert Dominique Bertrand Tomasz Haertlé 《Journal of Protein Chemistry》1994,13(2):143-149
Fourier transform infrared spectroscopy has been applied to investigate the secondary structural changes of-lactoglobulin in water/ethanol mixtures. The studies were carried out at two differentpHs and at high protein concentrations. The spectra were recorded using an attenuated total reflection cell. The amide I band of-lactoglobulin in water reveals large amounts of intra extended-sheet structure. About 20% ethanol,-lactoglobulin unfolds and-strand formation is observed.-Helices are built up by increasing the ethanol concentration up to 30%. In 50% ethanol,-lactoglobulin gels providing the apparent pH are neutral. The secondary structural changes of-lactoglobulin were observed on the similarity maps obtained by Principal Component Analysis. 相似文献
57.
Virginia Avellana-Adalid Gerard Rebel Michel Caron Jean-Denis Cornillot Dominique Bladier Raymonde Joubert-Caron 《Glycoconjugate journal》1994,11(4):286-291
The distribution of a 14.4 kDa S-type lectin was examined in murine neuroblastoma cells, either undifferentiated or after differentiation induced by dibutyryl-cyclic adenosine monophosphate. In undifferentiated cells the immunoreactivity was detected extracellularly, associated with the plasma membrane and in bulges released into the extracellular milieu. Important modifications of the lectin localization were associated with the differentiation process that induced an increased cytosolic expression and a decreased externalization. Possible functions for the lectin expressed intracellularly in the differentiated cells are also considered. 相似文献
58.
Peter Giesbrecht Thomas Kersten Heinrich Maidhof Dominique Krüger Peter Blümel Harald Grob Jörg Wecke 《Archives of microbiology》1994,161(5):370-383
In log-phase cells of staphylococci, cultivated under high, non-lytic concentrations of penicillin G, there occurred a novel killing process hitherto hidden behind seemingly bacteriostatic effects. Two events are essential for the apprearance of this hidden death: (i) the failure of the dividing cell to deposit enough fibrillar cross-wall material to be welded together, and (ii) a premature ripping up of incomplete cross walls along their splitting system. Hidden death started as early as 10–15 min after drug addition, already during the first division cycle. It was the consequence of a loss of cytoplasmic constituents which erupted through peripheral slit-like openings in the incomplete cross walls. The loss resulted either in more or less empty cells or in cell shrinkage. These destructions could be prevented by raising the external osmotic pressure. In contrast, the conventional non-hidden death occurred only much later and exclusively during the second division cycle and mainly in those dividing cells, whose nascent cross walls of the first division plane had been welded together. These welding processes at nascent cross walls, resulting in tough connecting bridges between presumptive individual cells, were considered as a morphogenetic tool which protects the cells, so that they can resist the otherwise fatal penicillin-induced damages for at least an additional generation time (morphogenetic resistance system). Such welded cells, in the virtual absence of underlying cross-wall material, lost cytoplasm and were killed via ejection through pore-like wall openings or via explosions in the second division plane and after liberation of their murosomes, as it was the case in the presence of low, lytic concentrations of penicillin. Bacteriolysis did not cause any of the hitherto known penicillin-induced killing processes.Dedicated to Prof. Dr. Georg Henneberg on the occasion of his 85th birthday 相似文献
59.
Luc Malaval Dominique Modrowski Ashwani K. Gupta Jane E. Aubin 《Journal of cellular physiology》1994,158(3):555-572
The regulation of cell surface fibroblast growth factor (FGF) receptors during the differentiation of F9 teratocarcinoma cells was investigated. The capacity of F9 cells to bind 125I-basic FGF (FGF-2) increased upon induction of differentiation with dibutyryl cAMP and retinoic acid. No change in binding capacity was observed in the first 24 h after addition of differentiating agents, but a sixfold increase in binding capacity was observed after 48 h and a fivefold increase after 72 h. Scatchard analysis of the binding data indicated that the increased binding of 125I-FGF-2 was due to an increase in the number of receptors with no change in their affinity. When 125I-FGF-2 was cross-linked to cell surface receptors, an increase in FGF-2-receptor complexes with molecular weights of 140,000–160,000 was also observed in the differentiated F9 cells. Undifferentiated F9 cells are known to secrete FGF-4 and cease expression of this molecule upon differentiation. To determine whether the low level of receptors in undifferentiated cells might be related to their production of FGF ligands, the ability of suramin, a drug that can disrupt FGF-receptor interactions, to modulate receptor number on F9 cells was investigated. Suramin treatment increased 125I-FGF-2 binding capacity of undifferentiated F9 cells threefold but had little effect on the binding capacity of differentiated cells. In addition, antibodies to FGF-4 increased the 125I-FGF-2 binding capacity of undifferentiated F9 cells by 58%. These results suggest that undifferentiated F9 cells might be responding in an autocrine manner to their own FGF ligands resulting in downregulation of cell surface FGF receptors. The increased number of receptors observed in differentiated cells may partly result from the decreased production of FGF ligands by these cells. © 1994 Wiley-Liss, Inc. 相似文献
60.
Stimulation of the Cyclic GMP Pathway by NO Induces Expression of the Immediate Early Genes c-fos and junB in PC12 Cells 总被引:7,自引:2,他引:5
Christelle Haby Fabrice Lisovoski Dominique Aunis Jean Zwiller 《Journal of neurochemistry》1994,62(2):496-501
Abstract: Stimulation of several second messenger pathways induces the expression of immediate early genes such as c- fos , c- jun , junB , and junD , but little is known about their induction via the stimulation of the cyclic GMP pathway. Here we looked at the expression of early genes in pheochromocytoma PC12 cells after activation of cytosolic guanylate cyclase by sodium nitroprusside. This compound spontaneously releases NO, a molecule known to be involved in cell communication. We found that expression of c- fos and junB but not of c- jun or junD is increased upon activation of cyclic GMP pathway. c- fos mRNA expression was the most activated (fourfold at 30 min), whereas junB response was more modest (2.2-fold activation at 60 min). Nuclear extracts of stimulated cells show increased binding capacity to the AP1 binding site consistent with the dose-response curve. The activating effect of nitroprusside could be reproduced by dipyridamole, a selective cyclic GMP phosphodiesterase inhibitor and by 8- p -chlorophenylthio-cyclic GMP, a permeant selective cyclic GMP-dependent protein kinase activator, and abolished by KT5823, an inhibitor of that kinase. The results show that NO promotes early gene activation and AP1 binding enhancement through the stimulation of the cyclic GMP pathway. 相似文献