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  • 76.60.Es  (3)
  • Escherichia coli  (3)
  • 1990-1994  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Sequence divergence of the murB and rrfB genes from Escherichia coli and Salmonella typhimurium (1994)
    Springer
    Archives of microbiology 161 (1994), S. 501-507 
    Details
    ISSN: 1432-072X
    Keywords: Escherichia coli ; Salmonella typhimurium ; murB ; rrfB ; Repetitive extragenic palindrome ; Evolution ; Mutation rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The murB gene of Salmonella typhimurium was cloned and found to be 75% and 82% identical to the DNA and protein sequences, respectively, of the same gene in Escherichia coli. These identities are among the lowest recorded between the two bacteria. Nevertheless, wild-type S. typhimurium murB complemented the known temperature-sensitive E. coli mutant, and wild-type E. coli murB complemented three temperature-sensitive mutants of S. typhimurium. The 5S rRNA gene, rrfB, and the region between murB and rrfB were also cloned and sequenced. The rrfB gene of S. typhimurium differs from rrfB of E. coli in only 2 of 120 nt, but the region between murB and rrfB has diverged greatly and includes a sequence that elosely resembles a repetitive extragenic palindrome of the type normally associated with E. coli. Previous comparisons of gene divergence have suggested that the chromosomal mutation rate is lower in the vicinity of the origin of replication. However, the S. typhimurium murB gene, located 6 map minutes from the origin of replication, is highly substituted at synonymous sites and the sequence between murB and rrfB is significantly modified as well. Thus, murB is an exception to the general observation that genes near the origin of replication show less divergence than do genes elsewhere in the bacterial chromosome.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00307771
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  • 2
    Electronic Resource
    Electronic Resource
    Transient, specific and extremely rapid release of osmolytes from growing cells of Escherichia coli K-12 exposed to hypoosmotic shock (1993)
    Springer
    Archives of microbiology 160 (1993), S. 424-431 
    Details
    ISSN: 1432-072X
    Keywords: Osmoadaptation ; Hypoosmotic shock ; Stretch-activated channels ; K+ release ; Glutamate release ; Trehalose release ; K+ uptake ; Glutamate uptake ; Amino-acid pool ; Accute osmotic stress ; Escherichia coli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of hypoosmotic shock on the solute content of growing Escherichia coli K-12 cells was investigated at 37°C. Within 20 s after the shock the cells had released most of their osmolytes K+, glutamate and trehalose. This release was specific and not due to rupture of the cell membrane, since under these conditions i) the cells neither lost protein nor ATP, ii)[14C]-labeled sucrose did not enter the cytoplasm from the periplasm, and iii) except for their glutamate and aspartate level, which decreased, the amino acid pool of alanine, lysine and arginine of the cells remained approximately constant. Within a minute after the shock the cells started to reaccumulate parts of their previously released glutamate, aspartate and K+, but not trehalose and resumed growth within 10 min after the shock. Experiments with K+-transport mutants showed that none of the genetically-identified K+ transport systems is involved in the K+-release process. Reaccumulation of K+ took place via the uptake systems TrkG and TrkH. The possibility is discussed that the exit of solutes after hypoosmotic shock occurs via several stretch-activated channels, which each allow the release of a specific osmolyte.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00245302
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  • 3
    Electronic Resource
    Electronic Resource
    Mutations affecting pore formation by haemolysin from Escherichia coli (1991)
    Springer
    Molecular genetics and genomics 226 (1991), S. 198-208 
    Details
    ISSN: 1617-4623
    Keywords: Haemolysin ; Escherichia coli ; Pore formation ; Site-specific mutation ; Lipid bilayer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary By introduction of site-specific deletions, three regions in HlyA were identified, which appear to be involved in pore formation by Escherichia coli haemolysin. Deletion of amino acids 9–37 at the N-terminus led to a haemolysin which had an almost threefold higher specific activity than wild-type and formed pores in an artificial asolectin lipid bilayer with a much longer lifetime than those produced by wild-type haemolysin. The three hydrophobic regions (DI–DIII) located between amino acids 238–410 contributed to pore formation to different extents. Deletion of DI led to a mutant haemolysin which was only slightly active on erythrocyte membranes and increased conductivity of asolectin bilayers without forming defined pores. Deletions in the two other hydrophobic regions (DII and DIII) completely abolished the pore-forming activity of the mutant haemolysin. The only polar amino acid in DI, Asp, was shown to be essential for pore formation. Removal of this residue led to a haemolysin with a considerably reduced capacity to form pores, while replacement of Asp by Glu or Asn had little effect on pore formation. A deletion mutant which retained all three hydrophobic domains but had lost amino acids 498–830 was entirely inactive in pore formation, whereas a shorter deletion from amino acids 670–830 led to a mutant haemolysin which formed abnormal minipores. The conductivity of these pores was drastically reduced compared to pores introduced into an asolectin bilayer by wild-type haemolysin. Based on these data and structural predictions, a model for the pore-forming structure of E. coli haemolysin is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00273604
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  • 4
    Electronic Resource
    Electronic Resource
    The electronic quantum size effect observed by195Pt NMR in the metal cluster compound Pt309Phen 36 * O30 (1993)
    Springer
    The European physical journal 26 (1993), S. 21-23 
    Details
    ISSN: 1434-6079
    Keywords: 74.30.Gn ; 74.70.Vy ; 76.60.Es
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 195Pt NMR on the organic ligand stabilized metal cluster compound Pt309Phen 36 * O30 reveals two separate peaks in the lineshape. Ligand-bonded platinum atoms at the surface of the core are thought to be responsible for the peak that does not show any Knight shift. The corresponding spin-lattice relaxation timeT 1 is of the order of seconds. The second peak is Knight shifted and is attributed to the other Pt atoms, for which metallic behavior is inferred from the temperature dependence ofT 1. The Korringa relation holds down to 65 K. Below 65 K the relaxation of the magnetization becomes increasingly non-exponential with decreasing temperature. The relaxation process can be successfully modelled under the assumption of a Poisson distribution of the energy levels around the Fermi energy (the electronic quantum size effect).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425605
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  • 5
    Electronic Resource
    Electronic Resource
    Solid state magic angle spinning13C and31P NMR of organic ligand stabilized high nuclearity metal clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 24-26 
    Details
    ISSN: 1434-6079
    Keywords: 74.30.Gn ; 74.70.Vy ; 76.60.Es
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 13C and31P solid state NMR measurements on the organic ligands in ligated Au55, Ni8, Pt309, Cu36 and Cu70 clusters are reported. The ligands behave like diamagnetic organic molecules, giving rise to relatively narrow lines with excellent cross-polarization efficiency. The resonance lines of the nuclei directly bound to the metal core are systematically broadened in the conducting compounds. No pronounced Knight shifts or evidence of metallic-like relaxation were observed. These results support a model for the electrical conduction involving tunneling between metal cores with the ligands playing the role of a tunneling barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425606
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  • 6
    Electronic Resource
    Electronic Resource
    NMR in metal cluster compounds compared to glasses (1991)
    Springer
    The European physical journal 20 (1991), S. 333-335 
    Details
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 76.60.Es
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The field and temperature dependence of the31P nuclear spin lattice relaxation rate in the metal cluster compound Ru55(P(t-Bu)3)12Cl20 follows a power law: 1/T 1 ∝T n B −m , withn=1.5±0.1 at 3.25 T andn=1.3±0.1 at 6.45 T;m ⋍ 1.4. Such dependences have so far only been observed in inorganic glasses and been attributed to two level systems. The correspondence suggests that the relaxation rate is due to interaction of theP-nuclear moment with electronic spins of stochastically moving charge carriers, which are thought to be responsible for the electrical conductivity through hopping between neigboring cluster molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544004
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