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  • 1
    Electronic Resource
    Electronic Resource
    Sediment type distribution in reservoirs: sediment source versus morphometry (1999)
    Springer
    Environmental geology 38 (1999), S. 101-110 
    Details
    ISSN: 1432-0495
    Keywords: Key words Reservoir sediments ; Sediment type ; Sediment source
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Bottom sediments were collected from seven Texas reservoirs to assess the spatial distribution of sediment types in reservoirs. The sediment samples were analyzed for water content, organic content, and grain-size distributions. The reservoirs are characterized by distinct water content patterns (referred to in this paper as Types I, II, and III) that reflect the lithologic units comprising their drainage area. The water content, organic content, and percent mud decreases from Type I (shale, marl) through Type II (limestone-marl-sandstone) to Type III (granite-gneiss-schist-sandstone) reservoirs. Reported elemental concentrations in the reservoir sediments are consistent with concentrations in the dominant rocks within their drainage area. While water depth accounts for part of the spatial distribution, sediment source explains the overall distribution of sediment types. Coarse-grained source rocks, multiple source rocks, and multiple tributaries which input sediment at different points contribute to an inconsistent sediment type distribution. Depending on the sediment source, sand and gravel-size sediments are present in the deeper regions of some reservoirs. This disrupts the classical morphometry (water depth, slope) controlled sediment distribution pattern (coarser sediments in shallower regions and finer sediments in deeper regions) of natural lakes. Thus, the location of tributaries and the type of sediments they carry are the dominant factors that control the sediment type distribution in reservoirs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002540050406
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  • 2
    Electronic Resource
    Electronic Resource
    Na+/H+ Exchanger Isoform 2 (NHE2) is Expressed in the Apical Membrane of the Medullary Thick Ascending Limb (1997)
    Springer
    The journal of membrane biology 160 (1997), S. 85-90 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Apical Na+/H+ exchangers (NHE) in the proximal tubule and medullary thick ascending limb (MTAL) display similar functions and regulation, suggesting that similar NHE isoforms are present. In the rat proximal tubule, NHE2 and NHE3 are present in the apical membrane, however, in the MTAL, NHE3, but not NHE2, mRNA has been found. In this study, the expression and subcellular localization of NHE2 in both rat and mouse MTAL were studied. To detect NHE2 mRNA, reverse transcription-polymerase chain reaction (RT-PCR) was performed in microdissected MTAL tubules using primers specific for NHE2. Analysis of PCR products with and without digestion by restriction enzymes chosen from the published NHE2 sequence gave predicted sizes. Subcloning and sequencing of the PCR product from mouse MTAL revealed 91% and 75% identity to the published NHE2 nucleotide sequence of comparable regions in rat and rabbit, respectively. Thus, NHE2 mRNA is expressed in the MTAL of mouse and rat. The subcellular localization of NHE2 was determined by immunochemistry using a specific NHE2 antibody. Immunofluorescence staining was observed in the apical, but not basolateral, membrane of MTAL of both species. In addition, anti-NHE2 antibody recognized an 85 kD protein in plasma membranes prepared from mouse and rat renal outer medulla and a MTAL cell line by Western analysis, which further support that NHE2 protein is expressed in the MTAL of both species. We conclude that NHE2 is expressed in the apical membrane of MTAL in both mouse and rat.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900297
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  • 3
    Electronic Resource
    Electronic Resource
    Expression of Na+/H+ Exchanger Isoforms in Inner Segment of Inner Medullary Collecting Duct (IMCD3) (1998)
    Springer
    The journal of membrane biology 164 (1998), S. 293-300 
    Details
    ISSN: 1432-1424
    Keywords: Key words: NHE — IMCD — IMCD3— RT-PCR — Hyperosmolality — Na+/H+ exchanger
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Na+/H+ exchangers (NHE) play a critical role in many cellular and transport processes in the inner medullary collecting duct (IMCD). Morphologically, the IMCD is divided into the outer (IMCD1), middle (IMCD2), and inner (IMCD3) segments. The inner, IMCD3 segment contains only one cell type, the IMCD cell, which is distinct in ultrastructure and in function from the principal and intercalated cells that are present in other portions of the IMCD. NHEs constitute a gene family containing several isoforms (NHE1, NHE2, NHE3, NHE4 and NHE5) which possess distinct characteristics and serve specialized functions. To understand the molecular basis of NHE-related processes in the IMCD, it is critical to know the molecular identity of the NHEs in this tubule segment. The purpose of the present study was to identify the NHE isoforms present and their polar distribution in IMCD3. Applying the reverse transcription-polymerase chain reaction (RT-PCR) technique to IMCD3 (obtained from distal 50% of inner medulla) of mouse and rat kidneys, we found that NHE1, NHE2 and NHE4, but not NHE3 were expressed in both species. The polar localization of NHE in IMCD3 was examined in tubules isolated from rats and perfused in vitro with HEPES-buffered solutions under isotonic conditions. pHi was measured by BCECF fluorescence. Na+-dependent, amiloride-inhibitable pHi recovery from cell acidification (consistent with NHE) was detected in the basolateral, but not the apical, membrane of IMCD3. We conclude that NHE1, NHE2 and NHE4, but not NHE3, are present in both the mouse and rat IMCD3. Functionally, NHE is limited to the basolateral membrane. Additional studies are needed to determine the physiological roles and regulation of basolateral NHE isoforms in this tubule segment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900414
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  • 4
    Electronic Resource
    Electronic Resource
    Generation of Campylobacter fetus S-layer protein diversity utilizes a single promoter on an invertible DNA segment (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 19 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Wild-type strains of Campylobacter fetus contain a monomolecular array of surface layer proteins (SLPs) and vary the antigenicity of the predominant SLP expressed. Reciprocal recombination events among the eight genomic SLP gene cassettes, which encode 97- to 149 kDa SLPs, permit this variation. To explore whether SLP expression utilizes a single promoter, we created mutant bacterial strains using insertional mutagenesis by rescue of a marker from plasmids. Experimental analysis of the mutants created clearly indicates that SLP expression solely utilizes the single sapA promoter, and that for variation C. fetus uses a mechanism of DNA rearrangement involving inversion of a 6.2 kb segment of DNA containing this promoter. This DNA inversion positions the sapA promoter immediately upstream of one of two oppositely oriented SLP gene cassettes, leading to its expression. Additionally, a second mechanism of DNA rearrangement occurs to replace at least one of the two SLP gene cassettes bracketing the invertible element. As previously reported promoter inversions in prokaryotes, yeasts and viruses involve alternate expression of at most two structural genes, the ability of C. fetus to use this phenomenon to express one of multiple cassettes is novel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1996.tb02469.x
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  • 5
    Electronic Resource
    Electronic Resource
    The Escherichia coli phage-shock-protein (psp) operon (1997)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 24 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The phage-shock-protein (psp) operon helps to ensure survival of Escherichia coli in late stationary phase at alkaline pH, and protects the cell against dissipation of its proton-motive force against challenge. It is strongly induced by filamentous phage pIV and its bacterial homologues, and by mutant porins that don’t localize properly, as well as by a number of other stresses. Transcription of the operon is dependent on σ54 and a constitutively active, autogenously controlled activator. psp-operon expression is controlled by one negatively and several positively acting regulators, none of which is a DNA-binding protein. The major product of the operon, PspA, may also serve as a negative regulator of an unusual porin, OmpG.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.3481712.x
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  • 6
    Electronic Resource
    Electronic Resource
    ADP-ribosylation by the extracellular fibrils of Myxococcus xanthus (1997)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 23 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The isolated, extracellular fibrils of the myxobacterium, Myxococcus xanthus, are capable of carrying out ADP-ribosylation. The substrate for the ADP-ribosylation is reactive with monoclonal antibody 2105, which has been shown to be directed specifically against the integral fibril proteins. The extracellular fibrils thus contain both the ADP-ribosyl transferase and the substrate for the ribosylation. This process may play a role in the contact-mediated cell–cell interactions that are an important part of the social behaviour of M. xanthus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.2111575.x
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular mechanisms of Campylobacter fetus surface layer protein expression[This paper] (1997)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 26 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Cells of the Gram-negative bacteria Campylobacter fetus are covered by monomolecular arrays of surface layer proteins (SLPs) critical for both persistence in their natural hosts and for virulence. For C. fetus cells, expression of SLPs essentially eliminates C3b binding and their antigenic variation thwarts host immunological defences. Each cell possesses multiple partially homologous and highly conserved SLP gene cassettes, tightly clustered in the genome, that encode SLPs of 97–149 kDa. These attach non-covalently via a conserved N-terminus to the cell wall lipopolysaccharide. Recent studies indicate that C. fetus reassorts a single promoter, controlling SLP expression, and one, or more, complete open reading frame strictly by DNA inversion, and that rearrangement is independent of the distance between sites of inversion. In contrast to previously reported programmed DNA inversion systems, inversion in C. fetus is recA- dependent. These rearrangements permit variation in protein expression from the family of SLP genes and suggest an expanding paradigm of programmed DNA rearrangements among microorganisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.6151958.x
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  • 8
    Electronic Resource
    Electronic Resource
    Autocides and a paracide, antibiotic TA, produced byMyxococcus xanthus (1996)
    Springer
    Journal of industrial microbiology and biotechnology 17 (1996), S. 424-431 
    Details
    ISSN: 1476-5535
    Keywords: M. xanthus ; antibiotic TA ; autocide ; paracide ; autolysis ; development ; focusin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Myxococcus xanthus produces two categories of low molecular weight antibacterial materials, autocides and paracides, that have diametrically opposite host ranges. Low concentrations of autocides lyseM. xanthus, the producing organism, whereas paracides exert their effects on other bacteria. Antibiotic TA (a paracide) kills all growing bacteria tested that have a peptidoglycan cell wall exceptM. xanthus. It is a macrocyclic polyketide with a molecular weight of 623. The two major autocides produced byM. xanthus are phosphatidylethanolamine and a mixture of fatty acids. The modes of action, host ranges and biosynthesis of antibiotic TA and the autocides are presented, and then an attempt is made to explain their role in the complex life cycle ofM. xanthus. In addition, the remarkable adhesion properties of antibiotic TA and a new semisynthetic derivative of it, focusin, are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01574773
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  • 9
    Electronic Resource
    Electronic Resource
    Deceptions in quasicrystal growth (1995)
    Springer
    Communications in mathematical physics 168 (1995), S. 337-352 
    Details
    ISSN: 1432-0916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract We discuss a new general phenomenon pertaining to tiling models of quasicrystal growth. It is known that with Penrose tiles no (deterministic) local matching rules exist which guarantee defect-free tiling for regions of arbitrary large size. We prove that this property holds quite generally: namely, that the emergence of defects in quasicrystal growth is unavoidable for all aperiodic tiling models in the plane with local matching rules, and for many models inR 3 satisfying certain conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02101553
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  • 10
    Electronic Resource
    Electronic Resource
    The relative reactivity of deoxyribose and ribose: Did DNA come before RNA? (1996)
    Springer
    Origins of life and evolution of the biospheres 26 (1996), S. 412-413 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02459842
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