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  • 1
    Electronic Resource
    Electronic Resource
    Cloned complementary deoxyribonucleic acid of Drosophila cells. Relationship of genome copy number to messenger ribonucleic acid abundance (1981)
    s.l. : American Chemical Society
    Biochemistry 20 (1981), S. 2651-2656 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00512a045
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  • 2
    Electronic Resource
    Electronic Resource
    Fidelity of chromatin transcription in vitro (1976)
    s.l. : American Chemical Society
    Biochemistry 15 (1976), S. 4356-4363 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00665a002
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  • 3
    Electronic Resource
    Electronic Resource
    Directional gene silencing induced by a complex subtelomeric satellite from Drosophila (1998)
    Springer
    Chromosoma 107 (1998), S. 311-320 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The telomeric regions in Drosophila cause transcriptional silencing of integrated transgenes. A complex satellite has recently been identified in the subterminal region of the left arm of chromosome 2 that is a good candidate for the source of the observed telomeric silencing, because genetically marked transposable elements that have inserted into this subtelomeric array show repression and variegation of the reporter gene. We asked whether this satellite can also cause transcriptional repression in ectopic chromosomal positions by placing it upstream of a mini-white reporter gene in P element constructs used for germ line transformation. The transgenes are shielded from external influences at the integration site using SU(HW) binding sites at either end. It was found that the satellite represses transcription of the reporter gene in an orientation dependent and an array length dependent manner. The satellite does not, however, induce variegation under the conditions used. The repressed transgenes do not respond to typical modifiers of centromeric position effect variegation, such as Su(var)205 5 , Su(var)2–1 1 , Su(var)3–1 1 , and Su(var)3–6 1 , or to the addition of a Y chromosome. However, as with the original variegating telomeric insertion, suppression in the transgenes is relieved by Su(z)2 5 , suggesting that suppression induced by the subtelomeric satellite retains aspects of telomeric silencing in ectopic positions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004120050313
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  • 4
    Electronic Resource
    Electronic Resource
    A telomeric satellite in Drosophila virilis and its sibling species (2000)
    Springer
    Chromosoma 109 (2000), S. 372-380 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Telomere elongation by telomerase is the most widespread mechanism among eukaryotes. However, alternative mechanisms such as homologous recombination between terminal satellite DNAs are probably used in lower dipteran insects and in some plants. Drosophila melanogaster uses the very unusual telomere elongation pathway of transposition of telomere-specific retrotransposable elements. The uniqueness of this telomere elongation mechanism raises the question of its origin. We, therefore, analyzed sequences located at telomeres of fairly distantly related Drosophila species, and in this paper we describe the characterization of complex satellite DNA sequences located at the telomeres of D. virilis and other species in the virilis group. We suggest an involvement of these DNA satellites in telomere elongation by homologous recombination similar to that found in lower dipterans. Our findings raise the possibility that telomere elongation by specific retrotransposons as found in D. melanogaster and its sibling species is a recent event in the evolution of dipteran insects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004120000094
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  • 5
    Electronic Resource
    Electronic Resource
    The genomic organization of HeT-A retroposons inDrosophila melanogaster (1993)
    Springer
    Chromosoma 102 (1993), S. 297-305 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Members of theDrosophila HeT-A family of transposable elements are LINE-like retroposons that are found at telomeres and in centric heterochromatin. We recently characterized an active HeT-A element that had transposed to a broken chromosome end fewer than mine generations before it was isolated. The sequence arerangement of this element, called 9D4, most likely represents the organization of an actively transposing member of the HeT-A family. Here we assess the degree of divergence among members of the HeT-A family and test a model of telomere length maintenance based on HeT-A transposition. The region containing the single open reading frame of this element appears to be more highly conserved than the non-coding regions. The HeT-A element has been implicated in theDrosophila telomere elongation process, because frequent transpositions to chromosome ends are sufficient to counter-balance nucleotide loss due to incomplete DNA replication. The proposed elongation model and the hypothetical mechanism of HeT-A transposition predict a predominant orientation of HeT-A elements with their oligo (A) tails facing proximally at chromosome ends, as well as the existence of irregular tandem arrays of HeT-A elements at chromosome ends resulting from transposition of new HeT-A elements onto chromosome ends with existing elements. Twenty-nine different HeT-A fragments were isolated from directional libraries that were enriched in terminal DNA fragments. Sequence analyses of these fragments and comparisons with the organization of the HeT-A element, 9D4, fit these two predictions and support the model ofDrosophila telomere elongation by transposition of HeT-A elements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00661272
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  • 6
    Electronic Resource
    Electronic Resource
    Comparison of two active HeT-A retroposons of Drosophila melanogaster (1994)
    Springer
    Chromosoma 103 (1994), S. 90-98 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. HeT-A elements are Drosophila melanogaster LINE-like retroposons that transpose to broken chromosome ends by attaching themselves with an oligo(A) tail. Since this family of elements is believed to be involved in the vital function of telomere elongation in Drosophila, it is important to understand their transposition mechanism and the molecular aspects of activity. By comparison of several elements we have defined here the unit length of HeT-A elements to be approximately 6 kb. Also, we studied an active HeT-A element that had transposed very recently to the end of a terminally deleted X chromosome. The 12 kb of newly transposed DNA consisted of a tandem array of three different HeT-A elements joined by oligo(A) tails to each other and to the chromosome end broken in the yellow gene. Such an array may have transposed as a single unit or resulted from rapid successive transpositions of individual HeT-A elements. By sequence comparison with another recently transposed HeT-A element, conserved domains in the single open reading frame (ORF), encoding a gag-like polypeptide, of these elements were defined. We conclude that for transposition an intact ORF is required in cis, while the reverse transcriptase is not encoded on the HeT-A element but is provided in trans. This would make HeT-A elements dependent on an external reverse transcriptase for transposition and establish control of the genome over the activity of HeT-A elements. This distinguishes the Drosophila HeT-A element, which has been implicated in Drosophila telomere elongation, from the other, 'selfish' LINE-like elements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352317
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  • 7
    Electronic Resource
    Electronic Resource
    Telomeric repeat sequences (1994)
    Springer
    Chromosoma 103 (1994), S. 154-161 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Chromosomes not only carry transcribed genes and their regulatory DNA sequences, but also contain regions that are required for the stability and maintenace of the chromosome as a unit. These include centromeres, telomeres and origins of replication. It is clear for replication origins and centromeres that the positions of these chromosomal organelles are determined by sites of the appropriate DNA sequences, but also that functional performance requires one or more contributing proteins. Telomeres are also structurally complex, with one or more DNA components, including simple telomeric repeats and more complex telomere-associated sequences, as well as one or more specific proteins that recognize these sequences. Accumulating evidence suggests that the simple telomeric repeats are required in most, but not all species, although they are not sufficient to determine the chromosomal position of a telomere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368007
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  • 8
    Electronic Resource
    Electronic Resource
    Chromosoma Focus (1997)
    Springer
    Chromosoma 106 (1997), S. 63-69 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Telomeres are nucleoprotein structures at the ends of eukaryotic chromosomes that perform a number of vital functions. They allow a cell to distinguish between natural chromosome ends and chromosome breaks in order to delay the cell cycle and repair the broken end. Telomeres also compensate for the inability of DNA polymerase to replicate the chromosome completely. In most eukaryotes a special reverse transcriptase, telomerase, adds telomeric DNA repeats to the chromosome ends using an internal RNA template. However, evidence is accumulating for alternative elongation mechanisms in a variety of eukaryotes. In the yeast Saccharomyces cerevisiae, and possibly in humans, both of which normally use telomerase, a different mechanism can be used for chromosome length maintenance when telomerase is inactive or inactivated. Yeast apparently uses recombination for this purpose; the mechanism in humans is not known. Some insect and plant species, on the other hand, do not use telomerase as their primary mechanism for maintaining chromosome length. Drosophila makes use of specific retrotransposons for this purpose, while other dipterans use recombination. We summarize here the current knowledge of these alternative telomere elongation mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004120050225
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  • 9
    Electronic Resource
    Electronic Resource
    Telomeric repeat sequences (1994)
    Springer
    Chromosoma 103 (1994), S. 154-161 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Chromosomes not only carry transcribed genes and their regulatory DNA sequences, but also contain regions that are required for the stability and maintenace of the chromosome as a unit. These include centromeres, telomeres and origins of replication. It is clear for replication origins and centromeres that the positions of these chromosomal organelles are determined by sites of the appropriate DNA sequences, but also that functional performance requires one or more contributing proteins. Telomeres are also structurally complex, with one or more DNA components, including simple telomeric repeats and more complex telomere-associated sequences, as well as one or more specific proteins that recognize these sequences. Accumulating evidence suggests that the simple telomeric repeats are required in most, but not all species, although they are not sufficient to determine the chromosomal position of a telomere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368007
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  • 10
    Electronic Resource
    Electronic Resource
    Comparison of two active HeT-A retroposons of Drosophila melanogaster (1994)
    Springer
    Chromosoma 103 (1994), S. 90-98 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract HeT-A elements are Drosophila melanogaster LINE-like retroposons that transpose to broken chromosome ends by attaching themselves with an oligo(A) tail. Since this family of elements is believed to be involved in the vital function of telomere elongation in Drosophila, it is important to understand their transposition mechanism and the molecular aspects of activity. By comparison of several elements we have defined here the unit length of HeT-A elements to be approximately 6 kb. Also, we studied an active HeT-A element that had transposed very recently to the end of a terminally deleted X chromosome. The 12 kb of newly transposed DNA consisted of a tandem array of three different HeT-A elements joined by oligo(A) tails to each other and to the chromosome end broken in the yellow gene. Such an array may have transposed as a single unit or resulted from rapid successive transpositions of individual HeT-A elements. By sequence comparison with another recently transposed HeT-A element, conserved domains in the single open reading frame (ORF), encoding a gag-like polypeptide, of these elements were defined. We conclude that for transposition an intact ORF is required in cis, while the reverse transcriptase is not encoded on the HeT-A element but is provided in trans. This would make HeT-A elements dependent on an external reverse transcriptase for transposition and establish control of the genome over the activity of HeT-A elements. This distinguishes the Drosophila HeT-A element, which has been implicated in Drosophila telomere elongation, from the other, ‘selfish’ LINE-like elements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352317
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