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  • 1
    Electronic Resource
    Electronic Resource
    Segmented Gene Conversion as a Mechanism of Correction of 18S rRNA Pseudogene Located Outside of rDNA Cluster in D. melanogaster (1997)
    Springer
    Journal of molecular evolution 44 (1997), S. 646 -651 
    Details
    ISSN: 1432-1432
    Keywords: Key words: Molecular evolution — Gene conversion — Ribosomal DNA — Pseudogene —Drosophila melanogaster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The peculiarities of the sequences of 18S rDNA included in a 90-kb DNA segment cloned in YAC vector are described. This heterochromatic segment is situated on the X chromosome distal to the main rDNA cluster. The pseudo 18S rDNA sequence comprised undamaged stretches of rDNA interspersed with segments characterized by high density of nucleotide substitutions and insertions/deletions. The observed patchwork arrangement of unaltered rDNA sequences was considered as evidence of segmented gene conversion events between the normal and damaged genes which are thought to constitute one of the mechanisms of rDNA array homogenization. The 18S rDNA fragment (510 bp) located nearby, homologous to the internal, undamaged part of pseudo 18S rDNA, carries comparable density of randomly distributed nucleotide substitutions with no evidence of correction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00006188
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Structure, molecular evolution and maintenance of copy number of extended repeated structures in the X-heterochromatin of Drosophila melanogaster (1994)
    Springer
    Chromosoma 103 (1994), S. 277-285 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The 60 kb repeats located in the distal heterochromatin of the X chromosome of Drosophila melanogaster were cloned in overlapping cosmids. These regions, designated as SCLRs, comprised the following types of repeated elements: Stellate genes, which are known to be involved in spermatogenesis; copia-like retrotransposons; LINE elements, including amplified Type I rDNA insertions; and rDNA fragments. The following steps in SCLR formation were hypothesized: insertion of mobile elements into the rDNA and Stellate gene clusters; internal tandem duplication events; recombination between the rDNA cluster and Stellate tandem repeat; and amplification of the whole SCLR structure. There are about nine SCLR copies per haploid genome, but there is approximately a twofold variation in copy number between fly stocks. The SCLR copy number differences between closely related stocks are suggested to be the result of unequal sister chromatid exchange (USCE). The restricted variation in SCLR copy number between unrelated stocks and the absence of chromosomes free of SCLRs suggests that natural selection is active in copy number maintenance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352252
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Structure, molecular evolution and maintenance of copy number of extended repeated structures in the X-heterochromatin of Drosophila melanogaster (1994)
    Springer
    Chromosoma 103 (1994), S. 277-285 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The 60 kb repeats located in the distal heterochromatin of the X chromosome of Drosophila melanogaster were cloned in overlapping cosmids. These regions, designated as SCLRs, comprised the following types of repeated elements Stellate genes, which are known to be involved in spermatogenesis; copia-like retrotransposons; LINE elements, including amplified Type rDNA insertions; and rDNA fragments. The following steps in SCLR formation were hypothesized: insertion of mobile elements into the rDNA and Stellate gene clusters: internal tandem duplication events; recombination between the rDNA cluster and Stellate tandem repeat; and amplification of the whole SCLR structure. There are about nine SCLR copies per haploid genome, but there is approximately a twofold variation in copy number between fly stocks. The SCLR copy number differences between closely related stocks are suggested to be the result of unequal sister chromatid exchange (USCE). The restricted variation in SCLR copy number between unrelated stocks and the absence of chromosomes free of SCLRs suggests that natural selection is active in copy number maintenance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352252
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Position-effect variegation in Drosophila melanogaster X chromosome inversion with a breakpoint in a satellite block and its suppression in a secondary rearrangement (1997)
    Springer
    Chromosoma 106 (1997), S. 520-525 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract.  In(1LR)pn2a is a pericentric inversion with a euchromatic breakpoint in the 2E polytene region and a heterochromatic breakpoint in the right arm of the X chromosome. It is associated with position-effect variegation (PEV) of the pn, wapl, Pgd and other vital loci of the 2E region, which are relocated near the bulk of the X heterochromatin. Cytological analysis showed that the rearrangement brings the 1A–2E euchromatic segment directly into contact with a major portion of the h34 block, a heterochromatic region that is positively stained by the N-banding technique and contains the AAGAG satellite sequences. Molecular cloning revealed the presence of a new junction between euchromatin and AAGAG satellite sequences and demonstrated that the euchromatic breakpoint of In(1LR)pn2a lies in the vinculin gene. In the X ray-induced secondary rearrangement In(1LR)r30, consisting of a pericentric inversion superimposed on In(1LR)pn2a, the h34 material remains associated with the 2E region but is separated from the rest of the X heterochromatin. In this case, the pn, wapl and Pgd loci no longer variegate, suggesting that the satellite-containing h34 region is not able per se to induce detectable PEV on the adjacent euchromatic genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004120050274
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  • 5
    Electronic Resource
    Electronic Resource
    Paralogous Stellate (2000)
    Springer
    Genetica 109 (2000), S. 131-140 
    Details
    ISSN: 1573-6857
    Keywords: concerted evolution ; Stellaterepeats ; Y chromosome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The X-linked Stellaterepeats, encoding a putative regulatory subunit of protein kinase CK2, are expressed in XO male testes. The Y-linked, testes-expressed paralogous Su(Ste) repeats are thought to be suppressors of Stellatetranscription. The unique, testis-expressed euchromatic gene was suggested to be an ancestor of the both types of amplified paralogous repeats. A Su(Ste)-like orphon was localized on a Y chromosome, outside of the Su(Ste) cluster. Several diagnostic molecular markers peculiar for the both types of diverged Stellateand Su(Ste) units were detected in the orphon sequence. The orphon was suggested to be a close relative of the immediate ancestor of both types of paralogous repeats which initiated evolution on the Y chromosome. Selection pressure on the level of translation was shown as a driving force in the evolution of Su(Ste) repeats, which are considered as more ancient derivatives of the ancestor euchromatic gene than Stellaterepeats. In a vicinity of 12E Stellatecluster the undamaged, recently originated euchromatic Stellateorphon was found at 12D, providing the poly(A) signal for the bendlessgene. P-element mediated transformations reveal that the fragments of cloned Stellateand Su(Ste) clusters are able to induce variegation of a reporter mini-whitegene. The observed variegation phenomenon has peculiar features: a significant increase of trans-activation of a reporter mini-whitegene in homozygous stat; absence of effects of several conventional modifiers of position effect variegation (PEV) and independence of a severity of variegation on a distance between insertion and centromere region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026596419250
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    Paper (German National Licenses)
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