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  • 1
    ISSN: 1432-0983
    Keywords: Key wordsATP9 and LSU introns ; Recombination ; ATP synthase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Specific mutations in nuclear MGI genes encoding the α, β and γ subunits of the mitochondrial inner membrane F1-ATPase complex allow mitochondrial DNA (mtDNA) to be lost from K. lactis. In the absence of a mutation in any of these three nuclear genes, loss of mtDNA is lethal. These results imply that mtDNA encodes a gene that is essential. Likely candidates for such an essential role are the ATP6, 8 and 9 genes coding for proteins of the ATP synthase-F0 component. The present study removes ATP9 from contention as a vital mitochondrial gene because in a respiratory deficient mutant, Gly– 3.9, lacking a nuclear mgi mutation, we have found that a rearrangement in mtDNA has deleted 22 amino acids from the carboxy terminus of the 75 amino-acid subunit-9 protein. Rearrangement in mtDNA has occurred by recombination at a 23-bp repeated sequence in the introns of the ATP9 and large ribosomal RNA (LSU) subunit genes. These two introns, of 394 (ATP9) and 410 (LSU) nucleotides, both belong to group 1.
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  • 2
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Ziel dieser Studie ist es, auf experimentellem Weg das Schichtungsphänomen in einem gleichförmig beheizten Horizontalkanal zu untersuchen. Die Schichtenbildung bei Zweiphasenströmung infolge Schwerkrafteinfluß und das hieraus resultierende thermohydraulische Verhalten wurden im Stationärbetrieb durch Messung von 16 Oberseiten- und 16 Unterseitentemperaturen analysiert. Es ließen sich sechs ausgezeichnete Wandtemperaturprofile feststellen, deren zugehörige Strömungsformmuster diskutiert werden. Eine dimensionslose Kennzahl wurde formuliert, deren Wertebereichen sich die verschiedenen Muster eindeutig zuordnen lassen.
    Notes: Abstract The objective of this study is to investigate experimentally the stratification phenomena of boiling two-phase flow in a uniformly heated horizontal channel. Two-phase flow stratification due to gravity effects, and consequently its thermal and hydrodynamic behavior, under steady state conditions, have been determined by measuring 16 top and 16 bottom wall temperatures. Six distinct wall temperature profiles are found, and the corresponding flow patterns are discussed. A dimensionless number has been formulated for the prediction of the occurrence of different flow patterns.
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  • 3
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Ziel dieser Studie ist es, auf experimentellem Weg das Schichtungsphänomen in einem gleichförmig beheizten Horizontalkanal zu untersuchen. Die Schichtenbildung bei Zweiphasenströmung infolge Schwerkrafteinfluß und has hieraus resultierende thermohydraulische Verhalten wurden im Stationärbetrieb durch Messung von 16 Oberseiten-und 16 Unterseitentemperaturen analysiert. Es ließen sich sechs ausgezeichnete Wandtemperaturprofile feststellen, deren zugehörige Strömungsformmuster diskutiert werden. Eine dimensionslose Kennzahl wurde formuliert, deren Wertebereichen sich die verschiedenen Muster eindeutig zuordnen lassen.
    Notes: Abstract The objective of this study is to investigate experimentally the stratification phenomena of boiling two-phase flow in a uniformly heated horizontal channel. Two-phase flow stratification due to gravity effects, and consequently its thermal and hydrodynamic behavior, under steady state conditions, have been determined by measuring 16 top and 16 bottom wall temperatures. Six distinct wall temperature profiles are found, and the corresponding flow patterns are discussed. A dimensionless number has been formulated for the prediction of the occurrence of different flow patterns.
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  • 4
    ISSN: 0392-6737
    Keywords: Fluid surfaces and fluid-fluid interfaces ; Phase transitions and critical phenomena ; Solid-fluid interfaces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Surface melting is strongly influenced by the interaction between the solid-liquid interface and the liquid-vapour interface. Unretarded electromagnetic dispersion forces yield a potential of the formH/l 2, wherel is the distance between the interfaces (thickness of the quasi-liquid film) andH is the appropriate Hamaker constant. We have adopted the well-known treatment of dispersion forces of Lifshitzet al., where the frequency-dependent conductivities of solid and liquid are the primary quantities for the calculation of this Hamaker constant. Using the dielectric functions obtained from experimental data, numerical values forH are obtained for Al, Pb, Au, Bi and Ge. The Hamaker constant of the metals is found to be positive and is discussed in connection with recent experimental data on surface melting, particularly of Pb(110) and Al(110). The Hamaker constants of Bi (semimetal) and Ge (semiconductor) are negative, allowing at most blocked surface melting.
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  • 5
    ISSN: 1420-908X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 6
    ISSN: 1420-908X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A cytofluorometric method was used to measure the number of IgE receptors available for binding and the native IgE content on microscopically identified peritoneal mast cells of Sprague-Dawley rats aged 4 to 25 weeks. During this period of growth, the mast cells increased progressively in size, granule mass and histamine content, but the number of IgE receptors did not increase in relation to body weight or age, although it varied greatly within the mast cell populations of individual rats as well as between the different rats. The peritoneal mast cells of these normal, naive, specific pathogen-free rats raised under controlled conditions and without signs of infections, were found to carry a significant number of IgE molecules of unknown specificity. The IgE content varied greatly among the individual mast cells within a given population, but, on average, as much as 74% of the receptors available for binding were occupied.
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  • 7
    ISSN: 1617-4623
    Keywords: Key wordsKluyveromyces lactis ; Lipoic acid ; Mitochondria ; LIPB gene ; F1-ATPase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mgi1-4 and mgi2-1 mutants of the petite-negative yeast Kluyveromyces lactis have mutations in the β- and α-subunits of the mitochondrial F1-ATPase, respectively. The mutants are respiratory competent but can form petites with deletions in mitochondrial DNA. In this study a cryptic nuclear mutation (lipB-1) was identified which, in combination with the mgi alleles, displays a synergistic respiratory-deficient phenotype on glycerol medium. The gene defined by the mutation was cloned and shown to encode a polypeptide of 332 amino acids with an N-terminal sequence characteristic of a mitochondrial targeting signal. The deduced protein shares 27% sequence identity with the product of the Escherichia coli lipB gene, which encodes a lipoyl-protein ligase involved in the attachment of lipoyl groups to lipoate-dependent apoproteins. A K. lactis strain carrying a disrupted lipB allele is severely compromised for growth on glycerol medium. The growth defect cannot be rescued by addition of lipoic acid, but cell growth can be restored on medium containing ethanol plus succinate. In addition, it was observed that lipB mutants of K. lactis, unlike the wild-type, are unable to utilize glycine as sole nitrogen source, indicating that activity of the glycine decarboxylase complex (GDC) is also affected. Taken together, these findings suggest that LIPB is the main determinant of the lipoyl-protein ligase activity required for lipoylation of enzymes such as α-ketoacid dehydrogenases and GDC.
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  • 8
    ISSN: 1617-4623
    Keywords: Key wordsKluyveromyces lactis ; MGI genes ; F1F0-ATP synthase ; F1 assembly ; F0 subunits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Specific mgi mutations in the α, β or γ subunits of the mitochondrial F1-ATPase have previously been found to suppress ρ0 lethality in the petite-negative yeast Kluyveromyces lactis. To determine whether the suppressive activity of the altered F1 is dependent on the F0 sector of ATP synthase, we isolated and disrupted the genes KlATP4, 5 and 7, the three nuclear genes encoding subunits b, OSCP and d. Strains disrupted for any one, or all three of these genes are respiration deficient and have reduced viability. However a strain devoid of the three nuclear genes is still unable to lose mitochondrial DNA, whereas a mgi mutant with the three genes inactivated remains petite-positive. In the latter case, ρ0 mutants can be isolated, upon treatment with ethidium bromide, that lack six major F0 subunits, namely the nucleus-encoded subunits b, OSCP and d, and the mitochondrially encoded Atp6, 8 and 9p. Production of ρ0 mutants indicates that an F1-complex carrying a mgi mutation can assemble in the absence of F0 subunits and that suppression of ρ0 lethality is an intrinsic property of the altered F1 particle.
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  • 9
    ISSN: 1617-4623
    Keywords: Mitochondrial DNA ; Kluyveromyces lactis ; MGM101/MGI genes ; Petite-negative yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Petite-negative yeasts do not form viable respiratory-deficient mutants on treatment with DNA-targeting drugs that readily eliminate the mitochondial DNA (mtDNA) from petite-positive yeasts. However, in the petite-negative yeastKluyveromyces lactis, specific mutations in the nuclear genesMGI2 andMGI5 encoding theα- andγ-subunits of the mitochondrial F1-ATPase, allow mtDNA to be lost. In this study we show that wild-typeK. lactis does not survive in the absence of its mitochondrial genome and that the function ofmgi mutations is to suppress lethality caused by loss of mtDNA. Firstly, we find that loss of a multicopy plasmid bearing amgi allele readily occurs from a wild-type strain with functional mtDNA but is not tolerated in the absence of mtDNA. Secondly, we cloned theK. lactis homologue of theSaccharomyces cerevisiae mitochondrial genome maintenance geneMGM101, and disrupted one of the two copies in a diploid. Following sporulation, we find that segregants containing the disrupted gene form minicolonies containing 6-8000 inviable cells. By contrast, disruption ofMGM101 is not lethal in a haploidmgi strain with a specific mutation in a subunit of the mitochondrial F1-ATPase. These observations suggest that mtDNA inK. lactis encodes a vital function which may reside in one of the three mitochondrially encoded subunits of F0.
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  • 10
    ISSN: 1617-4623
    Keywords: Key words F1-ATPase ; Mitochondrial DNA ; Petite mutation ; ρo lethality ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Although Saccharomyces cerevisiae can form petite mutants with deletions in mitochondrial DNA (mtDNA) (ρ−) and can survive complete loss of the organellar genome (ρo), the genetic factor(s) that permit(s) survival of ρ− and ρo mutants remain(s) unknown. In this report we show that a function associated with the F1-ATPase, which is distinct from its role in energy transduction, is required for the petite-positive phenotype of S. cerevisiae. Inactivation of either the α or β subunit, but not the γ, δ, or ɛ subunit of F1, renders cells petite-negative. The F1 complex, or a subcomplex composed of the α and β subunits only, is essential for survival of ρo cells and those impaired in electron transport. The activity of F1 that suppresses ρo lethality is independent of the membrane Fo complex, but is associated with an intrinsic ATPase activity. A further demonstration of the ability of F1 subunits to suppress ρo lethality has been achieved by simultaneous expression of S. cerevisiae F1α and γ subunit genes in Kluyveromyces lactis– which allows this petite-negative yeast to survive the loss of its mtDNA. Consequently, ATP1 and ATP2, in addition to the previously identified AAC2, YME1 and PEL1/PGS1 genes, are required for establishment of ρ− or ρo mutations in S. cerevisiae.
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