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41.
gltF, a member of the gltBDF operon of Escherichia coli, is involved in nitrogen-regulated gene expression 总被引:4,自引:0,他引:4
Irene Castaño † Noemi Flores Fernando Valle Alejandra A. Covarrubias Francisco Bolivar 《Molecular microbiology》1992,6(18):2733-2741
We report here the construction and analysis of insertional mutations in each of the three genes of the gltBDF operon and the nucleotide sequence of the region downstream from gltD. Two open reading frames were identified, the first of which corresponds to gltF. The gltB and gltD genes code for the large and small subunits, respectively, of the enzyme glutamate synthase (GOGAT). gltF codes for a protein, with a molecular mass of 26,350 Da, which is required for Ntr induction. Histidase synthesis was determined as a measure of Ntr function. First, insertions in gltB, gltD or gltF all prevent Ntr induction. Second, complementation analysis indicates that high-level expression of both the gltD and gltF genes is required for the induction of the Ntr enzymes under nitrogen-limiting conditions, indicating that the phenotype of the gltB insertion probably results from polarity on gltD and gltF. Third, glutamate-dependent repression of the glt operon appears to be mediated by the product of the gltF gene. Thus, the gltBDF operon of Escherichia coli is involved in induction of the so-called Ntr enzymes in response to nitrogen deprivation, as well as in glutamate biosynthesis. 相似文献
42.
43.
The relationship between biocontrol activity of Pseudomonas putida strain N1R against Pythium ultimum on pea and soybean seeds and the reduction in ethanol evolution by imbibed seeds was investigated under different treatment conditions, including temperature and numbers of seed‐applied cells of the bacterium. Treatment with strain N1R increased emergence at all temperatures, except for soybean at 12 °C and reduced ethanol concentration in the spermosphere of imbibed seeds at several temperatures. The concentration of bacterial cells in the seed treatment suspension also significantly affected biocontrol efficiency and reduced ethanol production, especially in pea seeds. In contrast, the duration (0–7 h) of submergence of seeds in bacterial suspension had little effect on biocontrol activity of N1R, although submergence of soybean seeds reduced their emergence even in the absence of the pathogen or biocontrol agent. Competition for seed‐derived compounds, including ethanol, is suggested to be one possible mechanism of biocontrol of Pythium by strain N1R, which is not known to produce antifungal antibiotics. 相似文献
44.
45.
The human platelet integrin GPIIb/IIIa (228 kDa), a Ca-dependent heterodimer formed by the IIb subunit (GPIIb, 136 kDa) and the 3 subunit (GPIIIa, 92 kDa), serves as the fibrinogen receptor at the surface of activated platelets. The degree of dissociation of the GPIIb/IIIa heterodimer (s°20
*, 8.9 S) into its constituent glycoproteins (GPIIb, 5.8 S; and GPIIIa, 3.9 S) has been assessed by analytical ultracentrifugation in Triton X100 buffers, and its Ca2+- and temperature-dependence correlated with Ca2+-binding to GPIIb/IIIa and its temperature dependence. At 21°C half-maximal dissociation of GPIIb/IIIa occurs at 5.5 ± 2.5 × 10–8 M Ca2+, very close to the dissociation constant of the high affinity Ca-binding site of GPIIb/IIIa (Kd1 8 ± 3 × 10–8 M) (Rivas and González-Rodríguez, 1991) and much lower than the Kd of the 3.4 medium affinity Ca-binding sites (Kd2 4 ± 1.5 × 10–5 M), which seems to demonstrate that the stability of the heterodimer in solution at room temperature is regulated by the degree of saturation of the high-affinity Ca-binding site. At 4°C, the stability of the heterodimer is apparently Ca2+-independent, while at room and physiological temperatures (15–37°C) the degree of dissociation of the heterodimer is regulated by the degree of dissociation of the high- and medium-affinity Ca-binding sites, respectively. On increasing the Ca2+ concentration up to 1 × 10–4 M after dissociation in Triton X100 solutions, the reconstitution of the GPIIb/IIIa heterodimer depends on the time and temperature at which the dissociated heterodimer was maintained, being almost complete within the first 5–10 min at 37°C and within the first 1–2 h at 21°C. After this time, a time- and temperature-dependent irreversible autoassociation of GPIIb (covalent) and GPIIIa (non-covalent) occurs, which hinders both the isolation of permanently stable monoamers of GPIIb and GPIIIa and the reconstitution of the GPIIb/IIIa heterodimer in Triton X100 solutions.
Abbreviations: GPIIb, GPIIIa, and GPIIb/IIIa, glycoprotein IIb, IIIa, and the heterodimer formed by them, respectively; s°20
*, the sedimentation coefficient of the glycoprotein-detergent complexes determined at 20°C, after extrapolation to zero-glycoprotein concentration
Offprint requests to: J. González-Rodríguez 相似文献
46.
Helicobacter pylori in Barrett's esophagus. 总被引:2,自引:0,他引:2
J C Ferreres F Fernández A Rodríguez Vives I González-Rodilla I Ursúa R Ramos J F Val-Bernal 《Histology and histopathology》1991,6(3):403-408
Barrett's esophagus is an anatomicoclinical state in which, due to the prolonged action of gastroesophageal reflux, the squamous epithelium is replaced by columnar epithelium. Helicobacter pylori has been implicated in the pathogenesis of various gastrointestinal disorders and has occasionally been observed in Barrett's esophagus. The aim of this study is to determine the incidence of H. pylori in Barrett's esophagus and try to establish its role in the pathogenesis of this disorder. H. pylori was observed in 31 biopsies (44.3%) of the 70 studied, mainly when the epithelium is of the gastric atrophic-fundic type (p less than 0.01). Its presence shows no relation to the degree of inflammatory activity and does not seem, therefore, to play an important role in the pathogenesis of the lesion. 相似文献
47.
Fernando G. de Mello Jan N. Hokoç Ana L. M. Ventura Patrícia F. Gardino 《Cellular and molecular neurobiology》1991,11(5):485-496
1. Retina-cell aggregate cultures expressed glutamate decarboxylase activity (L-glutamate 1-carboxylase; EC 4.1.1.15) as a function of culture differentiation. 2. Glutamic acid decarboxylase (GAD) activity was low in the initial phases of culture and increased eight-fold until culture day 7, remaining high up to day 13 (last stage studied). 3. The addition of GABA to the culture medium 24 h after cell seeding almost totally prevented the expression of GAD activity. 4. In association with decreased enzyme activity, aggregates exposed to GABA did not display immunoreactivity for GAD, suggesting that GAD molecules were either lost from GABAergic neurons or significantly altered with GABA treatment. 5. Control, untreated aggregates showed intense GAD immunoreactivity in neurons. Positive cell bodies were characterized by a thin rim of labeled cytoplasm with thickest labeling at the emergence of the main neurite. 6. Heavily labeled patches were also observed throughout the aggregates, possibly reflecting regions enriched in neurites. 7. The GABA-mediated reduction of GAD immunoreactivity was a reversible phenomenon and could be prevented by picrotoxin. 相似文献
48.
Hortensia Rico Enrique Herrero Fernando Miragall Rafael Sentandreu 《Archives of microbiology》1991,156(2):111-114
Depending upon growth temperature, Candida albicans can exhibit two different morphologies, a budding yeast or a mycelium. By studying the distribution of concanavalin A-ferritin particles on the cell wall surface during bud and germ tube formation, we have elucidated the way cell wall extension occurs. Both processes initially require the localized lysis of the wall in order to allow the incorporation of the newly synthesized material. Later on, the cell wall behaves as an elastic structure, allowing extension by an intosusception process and, as a consequence, cell growth.Abbreviation Con A
concanavalin A 相似文献
49.
Chinese hamster cells (Don line) were treated in vivo with 5-BrdU and 33258-Hoechst fluorochrome for obtaining the partial inhibition of condensation that causes the R-banding pattern. Untreated chromosomes were stained by a standard G-banding method. Statistical measurements show significant differences in the band numbers between the two treatments. The Don cell line in the authors' laboratory presents some karyotypical differences from Don cell lines studied by other authors. 相似文献
50.
Subunit arrangement in beef heart complex III 总被引:6,自引:0,他引:6
Beef heart mitochondrial complex III was separated into 12 polypeptide bands representing 11 different subunits by using the electrophoresis conditions described by Sch?gger et al. [(1986) Methods Enzymol. 126, 224-237]. Eight of the 12 polypeptide bands were identified from their NH2-terminal sequences as obtained by electroblotting directly from the NaDodSO4-polyacrylamide gel onto a solid support. The topology of the subunits in complex III was explored by three different approaches. (1) Protease digestion experiments of submitochrondrial particles in the presence and absence of detergent showed that subunits II and VI are on the M side of the inner membrane and subunits V and XI on the C side. (2) Labeling experiments with the membrane-intercalated probes [125I]TID and arylazidoPE indicated that cytochrome b is the predominant bilayer embedded subunit of complex III, while the non-heme iron protein appears to be peripherally located. (3) Cross-linking studies with carbodiimides and homobifunctional cleavable reagents demonstrated that near-neighbor pairs include subunits I+II, II+VI, III+VI, IV+V, V+X, and reagents demonstrated that near-neighbor pairs include subunits I+II, II+VI, III+VI, IV+V, V+X, and VI+VII. The cytochrome c binding site was found to include subunits IV, VIII, and X. The combined data are used to provide an updated model for the topology of beef heart complex III. 相似文献