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  • 1
    ISSN: 1432-0649
    Keywords: 42.60 ; 42.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract To improve the gain in the Orsay storage ring Free Electron Laser (FEL) experiment, the 17 period permanent magnet undulator has been modified to form an optical klystron (OK). We report the measurement of spontaneous emission and the effects on it of energy spread and angular spread. Gain and laser induced bunch lengthening measurements with the OK are also reported and are in very good agreement with the FEL classical theory. The spontaneous emission spectrum which is easy to measure with good signal to noise ratio, turns out to be a very good diagnostic tool forenergy spread and angular spread measurements on storage rings. The factor of four increase in the small gain obtained by converting the undulator NOEL into an OK was the critical factor in the recent operation of the ACO storage ring laser above threshold.
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  • 2
    ISSN: 1432-0649
    Keywords: 42.55T ; 29.20 ; 41.80D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper summarizes the basic low-current, laser-induced bunch-lengthening measurements that have been made on the ACO Storage-Ring Free-Electron Laser (SRFEL). The measurements provide verification of both the functional dependence and absolute magnitude of SRFEL theoretical models. The method of measurement, which is is explained, exploits frequency-domain techniques and is capable of accuracies comparable to those of a streak camara. The measurements are in good agreement with existing SRFEL theory and provide an important base for future work.
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  • 3
    ISSN: 1617-4623
    Keywords: Aminopterin ; 8-azaguanine ; Dihydrofolate reductase ; Hypoxanthine guanine phosphoribosyltransferase ; D. melanogaster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have studied the metabolic variability within different wild-type strains of Drosophila melanogaster for resistance to antimetabolites (aminopterin, 8-azaguanine), the target enzymatic activities (dihydrofolate reductase, hypoxanthine guanine phosphoribosyltransferase) and capacity to survive on minimal medium with or without exogenous bases or nucleosides (thymidine, hypoxanthine). No correlation was found between dihydrofolate reductase activity and resistance to aminopterin. The results indicated the importance of salvage pathways in the resistance mechanisms in Drosophila.
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  • 4
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have demonstrated the effect of different media on meiotic recombination in Drosophila melanogaster. Recombination is more frequent when the medium is deprived of bases, nucleosides and nucleotides. We have shown that two inhibitors of thymidylate (dTMP) synthesis —aminopterin inhibiting dihydrofolate reductase (DHFR) and fluorodeoxyuridine (FUdR) inhibiting thymidylate synthetase-result in a significant increase in meiotic recombination in the yellow/white region on the X chromosome of Drosophila melanogaster. Moreover the addition of thymidine to the richest medium significantly lowers normal recombination. Such studies represent a powerful tool for future studies on the mechanism of meiotic recombination.
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  • 5
    ISSN: 1617-4623
    Keywords: Key wordshobo dysgenic system ; Permissivity ; Drosophila melanogaster ; Variability ; Aging effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The hobo transposon is responsible for one of the three hybrid dysgenic systems that have been described in Drosophila melanogaster. Most studies on the hobo dysgenic system have been carried out using the PM system as a reference. However, these two systems differ significantly. In particular, several studies have failed to find any correlation between the molecular structures of hobo elements, the instability of the transposon and the incidence of gonadal dysgenic (GD) sterility. On the other hand, no study of the ability of females to permit hobo activity in their progeny when they are crossed with males harboring active hobo elements (permissivity) has yet been reported. In order to investigate the parameters involved in hobo permissivity, four E strains were studied with regard to the molecular nature of their hobo sequences and the GD sterility induced by a controlled source of hobo transposase. We show that hobo permissivity varies both within and between E strains. Moreover, permissivity decreases with age in E females. Our results are discussed with respect to similar phenomena that have been described in relation to the reactivity of the IR dysgenic system.
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  • 6
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The aim of our work was to compare the mechanisms of resistance to aminopterin, inhibitor of the dihydrofolate reductase enzyme, between different Drosophila species and those described for cultured cells. Moreover we compared the systematic species divisions based on morphological traits and those based on a molecular approach. For this purpose, the effect of aminopterin on viability and wing phenotype was studied in different Drosophila species. Dihydrofolate reductase was measured in adult flies. We found an important dihydrofolate reductase activity in the melanogaster sub-group compared to the other species studies. Wing effect was observed only in this sub-group. The effects of aminopterin on the wing phenotype were very similar to the phenotype of rudimentary mutants. Both deplete the pyrimidine pool and it has been shown by the studies of the structural genes of the nucleotide pyrimidine pathway that the wing tissue is very sensitive to every pertubation of this metabolism. The D. ananassae species was found to be fully resistant at the concentrations of the inhibitor tested. No or very little dihydrofolate reductase activity was detected. The binding of the enzyme to the inhibitor was comparable to that found in the Oregon strain of D. melanogaster. The purine and pyrimidine salvage pathways were investigated and the D. ananassae species displayed an important thymidine kinase activity. The D. ananassae flies were sensitive on Sang medium compared to the Oregon flies but were able to use exogenous bases or nucleosides more efficiently. Therefore the mechanism of resistance to aminopterin in Drosophila may be different from those described for methotrexate in mammalian cultured cells, as indicated by the results obtained for D. ananassae.
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  • 7
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Study of the action of aminopterin on genic recombination in Drosophila melanogaster—A study was made of the action, during meiosis, of aminopterin, inhibitor of nucleotide metabolism. An increase of the rate of crossing over was observed. This increase was studied on two systems, by using highly linked markers, so as to minimize the amount of double crossing over: vg-su, on chromosome II and y-w a, on the X chromosome. It is shown that aminopterin induces a significant increase of recombination. The independence of the two systems makes plausible that aminopterin could act on the whole genome at a meiotic level.
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  • 8
    ISSN: 1573-6857
    Keywords: evolution ; transposable element ; hobo ; Drosophila melanogaster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Hobo elements are a family of transposable elements found inDrosophila melanogaster and its three sibling species:D. simulans, D. mauritiana andD. sechellia. Studies inD. melanogaster have shown thathobo may be mobilized, and that the genetic effects of such mobilizations included the general features of hybrid dysgenesis: mutations, chromosomal rearrangements and gonadal dysgenis in F1 individuals. At the evolutionary level somehobo-hybridizing sequences have also been found in the other members of themelanogaster subgroup and in many members of the relatedmontium subgroup. Surveys of older collected strains ofD. melanogaster suggest that completehobo elements were absent prior to 50 years ago and that they have recently been introduced into this species by horizontal transfer. In this paper we review our findings and those of others, in order to precisely describe the geographical distribution and the evolutionary history ofhobo in theD. melanogaster complex. Studies of the DNA sequences reveal a different level of divergence between the groupD. melanogaster, D. simulans andD. mauritiana and the fourth speciesD. sechellia. The hypothesis of multiple transfers in the recent past into theD. melanogaster complex from a common outside source is discussed.
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