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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Trends in Genetics 6 (1990), S. 16-21 
    ISSN: 0168-9525
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Species of the genus Drosophila have been assigned to several subgenera, the largest of which are the Sophophora and the Drosophila. D. melanogaster is a species of the subgenus Sophophora, which is divided into four groups, obscura, saltans, willistoni and melanogaster, the last one being divided ...
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  • 3
    ISSN: 1617-4623
    Keywords: Drosophila melanogaster ; Hybrid ; dysgenesis ; I factor ; Transposition ; Complementation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Non-LTR retrotransposons, also known as LINEs, transpose by reverse transcription of an RNA intermediate. Their mechanism of transposition is apparently different from that of retrotransposons and similar to that of proviruses of retroviruses. The I factor is responsible for the I-R system of hybrid dysgenesis inDrosophila melanogaster. Inducer strains contain several functional I factors whereas reactive strains do not. Transposition of I factors can be experimentally induced: they are stable in inducer strains, but transpose at high frequency in the germline of females, known as SF females, produced by crossing reactive females and inducer males. We have constructed an I element, calledIviP2, marked with thevermilion gene, the coding sequence of which was interrupted by an intron. Splicing of the intron can only occur in the transcript initiated from the I element promoter. Transposed copies expressing a wild-typevermilion phenotype were recovered in the germline of SF females in which I factors were actively transposing. This indicates thattrans-complementation of a defective I element, deficient for the second open reading frame, by functional I factors can occur in the germline of dysgenic females.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1617-4623
    Keywords: Transposition ; Retroposon ; Reverse transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary I-R hybrid dysgenesis in Drosophila melanogaster occurs in female progeny of crosses between reactive strain females and inducer strain males, and is controlled by transposable elements called I-factors. These are 5.3 kb elements that are structurally similar to mammalian LINE elements and other retroposons. We have tested the activity of an I-factor directly, by introducing it into the genome of a reactive strain, using P-element mediated transformation. It confers the complete inducer phenotype on the reactive strain, and can stimulate dysgenesis when transformed males are mated with reactive females. It has transposed in the transformed lines, and we have cloned one of the transposed copies. This is the first time that it has been possible to demonstrate that a particular retroposon is transposition proficient, and to compare donor and transposed elements. We propose a mechanism for I-factor transposition based on these results, and the coding capacity of these elements. We have been unable to detect either autonomous transposition of a complete I-factor from a plasmid injected into reactive strain embryos, or transposition of a marked I-factor when co-injected with a complete element.
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  • 5
    ISSN: 1617-4623
    Keywords: Chromosomal rearrangements ; Drosophila melanogaster ; Hybrid dysgenesis ; I elements ; yellow gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report a detailed molecular analysis of three chromosomal rearrangements, which have been produced during I-R hybrid dysgenesis in Drosophila melanogaster. They all disrupt the yellow gene. One of them is a deletion; the other two are inversions, which may be interpreted as the results of recombination events between I elements inserted at their break points. These events appear to occur at the time of transposition and involve integrating rather than resident I elements. They are produced by a mechanism very similar to homologous ectopic recombination.
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 397 (1999), S. 101-101 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SirThe French scientific community is seriously worried about a furtively proposed government decree on the Centre National de la Recherche Scientifique (CNRS). Claude Allègre, the science minister, has proposed a sweeping reform without consulting the organization's ...
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  • 7
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Phylogenetic studies suggest that mobile element families are unstable components of the Drosophila genome. Two examples of immobilization of a transposable element family are presented here: as judged by their constant genomic organization among unrelated strains, the F and I element families have been respectively immobilized for a long time in D. simulans and in the reactive D. melanogaster strains (these are the laboratory strains which escaped the recent I invasion of D. melanogaster natural populations). All the elements of these defective families are located in the β heterochromatic portion of the genome. Moreover, most if not all of the β heterochromatic sequences into which the defective I elements are embedded are themselves non-mobile members of various nomadic families such as mdg 4, 297, 1731, F and Doc. These results are discussed with special emphasis on the possible nomadic origin of β heterochromatin components and on the mechanisms of evolutionary turnover of the transposable element families.
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  • 8
    ISSN: 1432-1432
    Keywords: Drosophila melanogaster ; Evolution ; Hybrid dysgenesis ; I elements ; Transposons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary There are two categories of strains inDrosophila melanogaster with respect to the I-R system of hybrid dysgenesis. The inducer strains contain particular transposable elements named I factors. They are not present in the strains of the other category called reactive (R) strains. Defective I elements are present in the pericentromeric regions of both categories of strains. This last subfamily of I sequences has not yet been described in detail and little is known about its origin. In this paper, we report that the defective I elements display an average of 94% of sequence identity with each other and with the transposable I factor. The results suggest that they cannot be the progenitors of the present day I factors, but that each of these two subfamilies started to evolve independently several million years ago. Furthermore, the sequence comparison of these I elements with an active I factor fromDrosophila teissieri provides useful information about when the deleted I elements became immobilized.
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  • 9
    ISSN: 1432-1432
    Keywords: Key words:Drosophila melanogaster— Retrovirus — Genomic organisation — Y chromosome — Heterochromatin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Gypsy is an endogenous retrovirus present in the genome of Drosophila melanogaster. This element is mobilized only in the progeny of females which contain active gypsy elements and which are homozygous for permissive alleles of a host gene called flamenco (flam). Some data strongly suggest that gypsy elements bearing a diagnostic HindIII site in the central region of the retrovirus body represent a subfamily that appears to be much more active than elements devoid of this site. We have taken advantage of this structural difference to assess by the Southern blotting technique the genomic distribution of active gypsy elements. In some of the laboratory Drosophila stocks tested, active gypsy elements were found to be restricted to the Y chromosome. Further analyses of 14 strains tested for the permissive vs. restrictive status of their flamenco alleles suggest that the presence of permissive alleles of flam in a stock tends to be associated with the confinement of active gypsy elements to the Y chromosome. This might be the result of the female-specific effect of flamenco on gypsy activity.
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  • 10
    ISSN: 1573-6857
    Keywords: envelope ; LTR-retrotransposon ; phylogeny ; polymorphism ; Ty3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The gypsy element of Drosophila melanogaster is the first retrovirus identified so far in invertebrates. According to phylogenetic data, gypsy belongs to the same group as the Ty3 class of LTR-retrotransposons, which suggests that retroviruses evolved from this kind of retroelements before the radiation of vertebrates. There are other invertebrate retroelements that are also likely to be endogenous retroviruses because they share with gypsy some structural and functional retroviral-like characteristics. Gypsy is controlled by a Drosophila gene called flamenco, the restrictive alleles of which maintain the retrovirus in a repressed state. In permissive strains, functional gypsy elements transpose at high frequency and produce infective particles. Defective gypsy proviruses located in pericentromeric heterochromatin of all strains seem to be very old components of the genome of Drosophila melanogaster, which indicates that gypsy invaded this species, or an ancestor, a long time ago. At that time, Drosophila melanogaster presumably contained permissive alleles of the flamenco gene. One can imagine that the species survived to the increase of genetic load caused by the retroviral invasion because restrictive alleles of flamenco were selected. The characterization of a retrovirus in Drosophila, one of the most advanced model organisms for molecular genetics, provides us with an exceptional clue to study how a species can resist a retroviral invasion.
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