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  • 1
    ISSN: 1573-6849
    Keywords: Beta vulgaris ; in situ hybridization ; LINE ; LTR retrotransposons ; non-LTR (non-viral) retrotransposons ; Ty1-copia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract DNA sequences of the reverse transcriptase gene of long terminal repeat (LTR) and non-LTR (non-viral) retrotransposons have been isolated and cloned from the genome of sugar beet (Beta vulgaris). Both retrotransposon types are highly amplified in sugar beet and may account for 2–5% of the genome. The BNR1 family, representing the first non-viral retrotransposon reported from a dicotyledonous species, shows homology to the mammalian L1 family of long interspersed repeated sequences (LINEs) and to retrotransposable elements from maize and lily. Sequences of the Tbv family are homologous to theTy1-copia class of LTR retrotransposons. The BNR1 and Tbv retrotransposon families are characterized by sequence heterogeneity and are probably defective. The deduced peptide sequences were used to investigate the relation to other retroelements from plants, insects and mammals. Fluorescencein situ hybridization was used to investigate the physical distribution and revealed that both retrotransposon families are present on all sugar beet chromosomes and largely excluded from chromosomal regions harbouring the 18S–5.8S–25S rRNA genes. The BNR1 family is organized in discrete clusters, while the Tbv family ofTy1-copia-like retrotransposons shows a more uniform distribution along chromosome arms and is absent from some chromosomal regions. These contrasting distributions emphasize the differences in evolutionary amplification and dispersion mechanisms between the two types of retrotransposons. Thein situ results of both elements reflect significant features of a higher order structure of the genome, as it is known for both short interspersed repeated sequences (SINEs) and LINEs in human.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5028
    Keywords: Beta procumbens ; Beta vulgaris ; in situ hybridization ; repetitive DNA ; satellite DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Members of three prominent DNA families of Beta procumbens have been isolated as Sau3A repeats. Two families consisting of repeats of about 158 bp and 312 bp are organized as satellite DNAs (Sau3A satellites I and II), whereas the third family with a repeat length of 202 bp is interspersed throughout the genome. Multi-colour fluorescence in situ hybridization was used for physical mapping of the DNA families, and has shown that these tandemly organized families occur in large heterochromatic and DAPI positive blocks. The Sau3A satellite I hybridized exclusively around or near the centromeres of 10, 11 or 12 chromosomes. The Sau3A satellite family I showed high intraspecific variability and high-resolution physical mapping was performed on pachytene chromosomes using differentially labelled repeats. The physical order of satellite subfamily arrays along a chromosome was visualized and provided evidence that large arrays of plant satellite repeats are not contiguous and consist of distinct subfamily domains. Re-hybridization of a heterologous rRNA probe to mitotic metaphase chromosomes revealed that the 18S-5.8S-25S rRNA genes are located at subterminal position on one chromosome pair missing repeat clusters of the Sau3A satellite family I. It is known that arrays of Sau3A satellite I repeats are tightly linked to a nematode (Heterodera schachtii) resistance gene and our results show that the gene might be located close to the centromere. Large arrays of the Sau3A satellite II were found in centromeric regions of 16 chromosomes and, in addition, a considerable interspersion of repeats over all chromosomes was observed. The family of interspersed 202 bp repeats is uniformly distributed over all chromosomes and largely excluded from the rRNA gene cluster but shows local amplification in some regions. Southern hybridization has shown that all three families are specific for genomes of the section Procumbentes of the genus Beta.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5028
    Keywords: Arabidopsis arenosa ; Cruciferae ; genus Arabidopsis ; in situ hybridization ; molecular systematics ; satellite DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have analysed a family of highly repetitive DNA from Arabidopsis arenosa (L.) Lawalrée [syn. Cardaminopsis arenosa (L.) Hayck] composed of AT-rich tandem repeats of 166–179 bp in head to tail organization. Sequence comparison between several repeat units revealed a high level of divergence of 4.5% to 25%. The sequence family shows more than 58% homology to satellite sequences described in Arabidopsis thallana (L.) Heynh. but no homology to other satellite repeats in the Cruciferae. Within the genus Arabidopsis the satellite sequence was found to be present in A. thaliana and Arabidopsis suecica (Fries) Norrlin, but not in Arabidopsis griffithiana (Boiss.) N. Busch and Arabidopsis pumila (Stephan) N. Busch. In situ hybridization to metaphase chromosomes of A. arenosa (2n=4x=32) showed the sequence to be localized at the centromeres of all 32 chromosomes with substantial hybridization along the chromosome arms. Using Southern hybridization and in situ hybridization, we give evidence that A. suecica is a hybrid of A. thaliana and A. arenosa. A considerable reorganization of the A. thaliana satellite sequence pAL1 occurred in the hybrid genome while no molecular change of the A. arenosa repeat was observed in the hybrid. Analysis of related repeats enabled differentiation between closely related genomes and are useful for the investigation of hybrid genomes.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-5028
    Keywords: Arabidopsis thaliana ; ferns ; in situ hybridization ; phylogenetics ; pines ; reverse transcriptase genes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have investigated the physical distribution of the reverse transcriptase genes of Ty1-copia-like retrotransposable elements from 12 plant species belonging to different subdivisions by hybridization in situ on chromosome preparations. Ty1-copia-like elements showed different and non-random hybridization patterns. A dispersed distribution throughout most of the chromosomes with reduced hybridization at some regions or with some weak clustering at other regions was found in Allium cepa, Beta vulgaris, Brassica campestris, Brassica oleracea, Pennisetum glaucum, Pinus elliottii, Selaginella apoda, Vicia faba and Vicia narbonensis. Reduced hybridization occured mainly at centromeric regions, nucleolus-organizing regions and regions known to be mainly composed of tandemly repeated sequences. In the fern Pteris cretica the retroelements showed a dispersed genomic organization with clustering at some chromosomal regions and whole chromosomes showing little signal. In Arabidopsis thaliana and Cicer arietinum, Ty1-copia-like elements were found in clusters at the paracentromeric heterochromatin, a novel organization for a repetitive element in A. thaliana. New retroelement families were isolated from A. thaliana and from Beta vulgaris. Alignment of the deduced peptide sequences with Ty1-copia-like elements from other plants showed considerable divergence which was used to calculate their relationships, indicating the value of reverse transcriptase gene analysis in phylogenetic and biodiversity studies.
    Type of Medium: Electronic Resource
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