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  • Articles  (28)
  • 1995-1999  (26)
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  • Biology  (28)
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  • 1
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 31 (1999), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Diffusely adhering Escherichia coli (DAEC) strains have been implicated in epidemiological studies as a cause of diarrhoea in children. However, the molecular interactions of these pathogens with target cells have remained largely obscure. We found that some DAEC strains contain homologues of the locus of enterocyte effacement (LEE) pathogenicity island and secrete EspA, EspB and EspD proteins necessary for the formation of the attaching and effacing (A/E) lesions. To characterize the function of the EspD protein further, we cloned and sequenced the espD genes of two DA-EPEC strains and compared their deduced amino-acid sequences with known EspD sequences. A pattern of two conserved transmembrane regions and one conserved coiled-coil region is predicted in EspD and also in the type III system secreted proteins YopB, PopB, IpaB and SipB of Yersinia, Pseudomonas, Shigella and Salmonella respectively. The EspD protein is inserted into a trypsin-sensitive location in the HeLa cell membrane at sites of bacterial contact, but is not translocated into the cytoplasm. Secretion of EspD increases upon contact with host cells. We propose that the membrane-located EspD protein is part of the translocation apparatus for Esp proteins into the target host cell performing functions similar to YopB in Yersinia.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 22 (1996), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The AIDA-I adhesin known to be responsible for the diffuse adherence (DA) phenotype of the diarrhoea-genie Escherichia coli (DAEC) strain 2787 has been shown previously to be synthesized as a precursor protein and to undergo additional C-terminal processing. Here, the C-terminal processing of the AIDA-I precursor and the outer membrane topology of the cleaved C-terminal fragment, AIDAC, were investigated. By isolation of the cleaved AIDAC fragment and N-terminal sequencing, the C-terminal cleavage site was identified between Ser-846 and Ala-847 thereby indicating a molecular mass of 47.5 kDa for AIDAC. The correct processing to AIDA-I and AIDAC in OmpT, OmpP and DegP protease-deficient E. coli strains as well as in avirulent salmonellae and shigellae points to an autocatalytic cleavage mechanism. The cleaved AIDAC was localized in the outer membrane. A leader sequence-AIDAC fusion was efficiently routed to the outer membrane. Analysis by protease digestion, secondary-structure prediction and modelling, by comparison with structurally related bacterial proteins like the lgA1 protease from neisseria, the vacuolating toxin from Helicobacter pylori, and the VirG protein of Shigella flexneri, strongly indicates that AIDAC is present in the outer membrane as a β-barrel structure.
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 383 (1996), S. 401-401 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR á€" Microhardness measurements on synthesized samples of stishovite, a high-pressure phase of silica, show that it is the hardest oxide yet discovered. Among polycrystalline materials, its hardness (33 gigapascals, GPa) rivals those of the hardest materials. Despite many ...
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 170 (1999), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We have explored the nature of the sudden viral amplification observed during the ageing of P22-infected lysogenic colonies of Salmonella typhimurium [Ramı́rez, E, and Villaverde, A. (1997) Gene 202, 147–149]. By a comparative analysis of the wild-type P22 and a P22 integration mutant, it has been shown that the conditions promoting prophage induction occur in only a small portion of the bacterial population and briefly during the transition between the exponential growth and the stationary phase. The viral burst is RecA-dependent and cannot be reproduced in continuous culture by a mere decrease of the growth rate. This suggests that the limited viral propagation in colonies is probably linked to heterogeneous physiological conditions within colonial populations, distinct from those of the homogeneous liquid cultures.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 178 (1996), S. 605-628 
    ISSN: 1432-1351
    Keywords: Crustacean ; Olfaction ; Mechanoreception ; Local interneurons ; Projection neurons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Neurons in the olfactory deutocerebrum of the spiny lobster, Panulirus argus, were recorded intracellularly and filled with biocytin. Recorded neurons arborized in the olfactory lobe (OL), a glomerular neuropil innervated by olfactory and some presumptive mechanosensory antennular afferents. The neurons responded to chemosensory input from the lateral antennular flagellum bearing the olfactory sensilla but not the medial flagellum bearing many non-olfactory chemosensory sensilla. Many neurons received additional mechanosensory input. Thus the OL integrates specifically olfactory with mechanosensory input. OL neurons had multiglomerular arborizations restricted to one or two of the three horizontal layers of the columnar glomeruli. OL local interneurons comprised “core” neurons with tree-like neurites and terminals in the base of the glomeruli and “rim” neurons with neurites surrounding the OL and terminals in the cap/subcap. The somata of OL local interneurons lay in the medial soma cluster (100000 somata). OL projection neurons arborized in the base of the glomeruli and ascended via the olfactory glomerular tract to the lateral protocerebrum. A parallel projection pathway is constituted by projection neurons of the accessory lobe, a glomerular neuropil without afferent innervation but intimate links to the OL. The projection neuron somata constituted the lateral soma cluster (200000 somata).
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 178 (1996), S. 579-604 
    ISSN: 1432-1351
    Keywords: Crustacean ; Chemoreception ; Mechanoreception ; Deutocerebrum ; Motoneurons ; Projection neurons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Neurons in the brain of the spiny lobster that respond to chemical and mechanical stimulation of the antennule (antenna I) were recorded and stained intracellularly. Described here are neurons that do not arborize in the olfactory and accessory lobes of the deutocerebrum, but rather primarily target the lateral and/or the median antennular neuropils of the deutocerebrum. Some of the neurons also extend into the antennal and tegumentary neuropils of the tritocerebrum and the neuropils of the median protocerebrum. Included are antennular sensory afferents, antennular motoneurons, projection neurons descending from the central brain, projection neurons ascending from the central brain and projection neurons descending from the eyestalk ganglia. Collectively, these neurons consitutute a novel antennular sensory pathway that is parallel to and independent of the antennular olfactory pathway. The novel pathway integrates mechanosensory and non-olfactory chemosensory information in the lateral and/or the median antennular neuropils, which also serve as lower motor centers of the antennule. Division of the arthropod deutocerebrum into two, functionally distinct chemosensory pathways may reflect differences in how chemosensory information is processed that is fundamental to understanding the origin of the sense of smell.
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  • 7
    ISSN: 1432-2048
    Keywords: Chaperone ; Chloroplasts ; Chromoplasts ; Heat-shock protein ; Secale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A partial cDNA which codes for the β-subunit of a plastidic chaperonin 60 (cpn60-β) from rye (Secale cereale L.) leaves was identified and sequenced, except for 46 amino acids of the N-terminus of the mature protein and the transit sequence. This is the first cpn60-β sequence determined for a monocotyledonous plant. Specific antibodies against cpn60-β were affinity-purified from an antiserum raised against the total soluble protein fraction of ribosome-deficient plastids. The localization of cpn60-β in chloroplasts or non-green plastids was confirmed by immunodetection in Percoll gradient-purified organelles. The expression and occurrence of cpn60-β was analysed by immunoblotting with the specific antibodies and Northern hybridization. The cpn60-β protein was constitutively expressed in various green and non-green tissues. It was evenly distributed along the major part of a rye leaf, while highest transcript levels occurred in the youngest and oldest leaf sections. The expression of the cpn60-β protein was not enhanced by a heat-shock treatment at 42 °C. The cpn60-β transcript and protein were more strongly expressed in various non-green, for instance etiolated, 70S-ribosome-deficient 32 °C-grown, or herbicide-bleached tissues, than in green leaves of rye. A rapid increase in the cpn60-β transcript level was also observed when green leaves were transferred from light to darkness while the protein level was not affected. The dark-induced increase in the cpn60-β transcript was totally suppressed in the presence of 2% sucrose. Inhibitor treatments suggested that the change in cpn60-β transcript level was not related to changes of the ATP supply of the tissue. While the large subunit of the photosynthetic protein ribulose-1,5-bisphosphate carboxylase was largely degraded during ripening of tomato fruits, high levels of cpn60-β were detected in tomato chromoplasts and in the yellow flower petals of Narcissus. Low levels of cpn60-β were detected in root tissue.
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  • 8
    ISSN: 1432-0983
    Keywords: Key words Petite mutation ; Error-prone repair ; Paraquat ; Psoralen photo-induced DNA-damage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The original pso3-1 mutant isolate of the yeast Saccharomyces cerevisiae exhibits a pleiotropic mutagen-sensitivity phenotype that includes sensitivity to UVA-activated 3-carbethoxypsoralen, to UVC-light, to mono- and bi-functional nitrogen mustard, to paraquat, and to cadmium; on the other hand, it shows hyper-resistance (HYR) to nitrosoguanidine when compared to established wild-type strains. Also, the original pso3-1 mutant exhibits a low UVC-induced mutability and mitotic gene conversion and a high rate of spontaneous and UVC-induced petite mutations. Since the HYR to the nitrosoguanidine (MNNG) phenotype resembles that of low glutathione-containing yeast cells, the original pso3-1 mutant was crossed to a gsh1 knock-out mutant that lacks the enzyme for the first step in glutathione biosynthesis and the resulting diploid was tested for complementation. While there was none for HYR to nitrosoguanidine, and other low glutathione-related phenotypes, some other phenotypic characteristics of pso3-1, e.g. UVC sensitivity and UVC-induced mutability were restored to a wild-type level. Tetrad analysis of a diploid derived from a cross of the original haploid pso3-1 isolate with a repair-proficient, normal glutathione-containing, PSO3 GSH1 wild-type led to the separation of a leaky gsh1 mutation phenotype from that of the repair-deficient pso3-1 phenotype. Linkage studies by tetrad and random spore analyses indicated no linkage of the two genes. This shows that the low glutathione content in the original pso3-1 isolate is due to a second, additional, mutation in the GSH1 locus and is unrelated to the pso3-1 mutation. Thus, the original pso3-1 isolate is a pso3-1 gsh1 double mutant with most of the particular characteristics of the pleiotropic sensitivity phenotype contributed by either the pso3-1 or the gsh1-leaky mutant allele. The expression of a few phenotypic characteristics of pso3, however, were most pronounced in pso3-1 mutants with a low glutathione pool.
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  • 9
    ISSN: 1432-1017
    Keywords: Iron superoxide dismutase ; SOD ; X-ray absorption ; XAS ; Extended X-ray absorption fine structure ; EXAFS ; P. shermanii ; E. coli ; Metalloproteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The local structure of the iron site in ferric superoxide dismutase from P. shermanii was analyzed by X-ray absorption spectroscopy. The metal-ligand cluster of the enzyme is found to be similar to the crystallographically investigated ferric superoxide dismutase from E. coli. At pH 6.4 the enzyme is five-fold coordinated with three histidines, an aspartate and a water molecule. The average bond lengths between the metal and the histidines are about 2.10 Å, between metal and aspartate they are about 1.86 Å and between metal and water 1.96 Å. With an increase in pH a change in the coordination number from five to six is observed both in pre-edge peak and EXAFS spectra analysis. However, the bond lengths of the ligands do not change dramatically, they are conserved for the aspartate and increase slightly to 2.13 Å for the average metal - histidine distance at pH 9.3. The observation of the increase in coordination number is correlated with a decrease in enzymatic activity which occurs in the high pH range. The zinc EXAFS spectra of P. shermanii superoxide dismutase have shown that zinc can be incorporated in the active center instead of the iron.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 182 (1998), S. 677-686 
    ISSN: 1432-1351
    Keywords: Key words Electrophysiology ; Brain ; Insect ; Histamine ; GABA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Whole-cell patch-clamp recordings were obtained from 116 freshly dissociated neuronal somata from the optic lobe of adult locusts (Schistocerca gregaria). Prerequisites were a papain treatment and the directed transfer of somata to the recording chamber by dabbing. Of the recorded somata, 65 were from lamina and 51 from other optic lobe neurons. All somata supported voltage-activated outward currents and some (24% of optic lobe, 3% of lamina neurons) also fast inward currents. Most lamina neurons supported an outward current that activated (V 1/2=−8.5 mV) and inactivated rapidly and a sustained outward current. Some lamina and most optic lobe neurons expressed only a sustained outward current (V 1/2=−9.4 mV). GABA and histamine elicited inward currents at negative holding potentials. Most optic lobe (95%) but only 18% of lamina neurons showed a γ-aminobutyric acid (GABA) current, whereas a similar percentage of optic lobe (50%) and lamina neurons (67%) expressed a histamine current. Both currents reversed near the chloride equilibrium potential, were reversibly reduced by picrotoxin, and did not show rundown. Thus, they likely represent chloride currents mediated by ionotropic receptors. Our data indicate that the lamina neurons recorded mainly represent monopolar cells postsynaptic to histaminergic photoreceptors. The optic lobe neurons, on which GABA and histamine apparently act as inhibitory neurotransmitters, are more heterogeneous.
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