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  • 1
    Electronic Resource
    Electronic Resource
    T-DNA integrations in a new family of repetitive elements of Nicotiana tabacum (1995)
    Springer
    Journal of molecular evolution 41 (1995), S. 498-504 
    Details
    ISSN: 1432-1432
    Keywords: T-DNA ; Integration ; Tobacco ; Repetitive sequences ; Transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A number of T-DNA insertions in the genome of Nicotiana tabacum were characterized. One class of integrations was found to have occurred in a new family of highly repetitive sequences. Three genomic regions (ecoA, ecoB, and ecoC) were isolated, all of which contain basic units of 180 bp, organized in direct tandem repeats. Several of the 180-bp elements contain an EcoRI recognition site within the repeating unit and are therefore named “eco repeats.” All members of this family are weakly homologous in sequence to a previously described class of repeat elements which contained a BamHI site (HRS60 repeat family), which suggests that both groups of sequences are of common evolutionary origin. The allotetraploid genome of N. tabacum is presumed to originate from the hybridization of two diploid genomes. The HRS60 elements previously described have been found exclusively in the genome of one of the ancestors, N. sylvestris, and in N. tabacum itself. Our DNA hybridization data suggest that the eco elements originate from the genome of the other ancestor, N. tomentosiformis. Whereas the HRS60 elements are transcriptionally silent, at least some eco elements appear to be transcribed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00160322
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  • 2
    Electronic Resource
    Electronic Resource
    NTRS, a new family of highly repetitive DNAs specific for the T1 chromosome of tobacco (1997)
    Springer
    Chromosoma 106 (1997), S. 369-379 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Species-specific repeated DNAs are important for identifying genomic components of hybrid organisms in plant breeding and in taxonomic studies, and we have previously described the HRS60 and GRS families of highly repetitive DNA sequences in tobacco. Here we describe a new family of highly repetitive DNA sequences termed NTRS (SspI family) that we have isolated from Nicotiana tomentosiformis (Goodspeed) and characterized and that is specific for the genomes of several species of the subgenus Tabacum. In situ hybridization showed that NTRS sequences are present in three pairs of chromosomes of N. tomentosiformis, six pairs of chromosomes of N. kawakamii, and only one pair of chromosomes of N. tabacum at an intercalary site. The NTRS family is not present in the N. otophora genome. The majority of NTRS sequences appeared to be organized in tandem arrays in which local DNA structures sensitive to single strand-specific chemical probes, potassium permanganate, and osmium tetroxide complexed with pyridine revealed a periodicity of 220 bp, equal to the length of the repeat unit. The inner cytosine in CCGG and CC(A/T)GG sequences of the NTRS family is frequently methylated. Cloned and sequenced NTRS monomeric units are 212–219 bp in length and show 83.5%–95% mutual homology. They exhibit properties characteristic for molecules that possess stable intrinsic curvature, but there are differences among individual monomers in the degree of curvature. NTRS sequences like HRS60 and GRS sequences, were found to specify nucleosome positions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004120050258
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  • 3
    Electronic Resource
    Electronic Resource
    The influence of 5-azacytidine on the condensation of the short arm of rye chromosome 1R in Triticum aestivum L. root tip meristematic nuclei (1997)
    Springer
    Chromosoma 106 (1997), S. 485-492 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract.  This paper describes the effects of 5-azacytidine on the condensation state of rye (Secale cereale L.) chromatin introduced into the wheat genome (Triticum aestivum L. cv. Beaver). The wheat cultivar Beaver carries a translocation between the short arm of rye chromosome 1R (1RS) and the long arm of wheat chromosome 1B (1BL/1RS). 1RS can be detected using genomic in situ hybridisation and carries a ribosomal DNA (rDNA) locus that can be simultaneously detected using multiple labelling strategies. The rDNA locus divides 1RS into a distal region that is gene rich and a proximal region that is gene poor and highly methylated. 1RS also carries a large block of subtelomeric heterochromatin. The drug, which acts to inhibit DNA methylation in plants, has three pronounced effects on interphase nuclei. (1) It induces aberrant condensation of the rye subtelomeric heterochromatin and in many cases induces sister chromatid separation in the subtelomeric heterochromatin of G2 nuclei. (2) Nuclei trisomic for 1RS are observed at low frequency in treated material and are probably a consequence of aberrant sister chromatid separation or condensation. (3) The drug alters normal condensation of 1RS euchromatin. However, contrary to expectation the effect is not simply to induce decondensation. The proximal region of the arm actually condenses at low levels of drug administration while the distal region remains unaltered or increases its decondensation state. Increasing the concentration of 5-azacytidine induces a biphasic response and at the highest concentration used all regions of the arm show signs of decondensation. Thus the influence of the drug on chromatin condensation depends on the genomic structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00007688
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of a new family of tobacco highly repetitive DNA, GRS, specific for theNicotiana tomentosiformis genomic component (1995)
    Springer
    Chromosome research 3 (1995), S. 245-254 
    Details
    ISSN: 1573-6849
    Keywords: Nicotiana tabacum ; nucleosome positioning ; Progenitor-specific probes ; repetitive DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Members of a new family of highly repetitive DNA sequences called GRS were isolated fromNicotiana tabacum L. genomic DNA and characterized. Cloned, sequenced monomeric units (180–182 bp) of GRS exhibit properties characteristic of molecules that possess a stable curvature. The GRS family represents about 0.15% of total genomic DNA (104 copies per haploid genome) and could be derived from eitherNicotiana tomentosiformis orNicotiana otophora, two possible ancestors of the T genome of the amphidiploidN. tabacum. Sequence homology between the HRS60 (Koukalováet al. 1989) and the GRS family has been estimated to be 57%.In situ hybridization was used to localize GRS on mitotic chromosomes. Hybridization signals were obtained on five pairs of chromosomes at intercalary sites of the longer chromosome arms. The majority of GRS sequences appeared to be organized in tandem arrays and a minority were found to be dispersed through the genome in short clusters, interspersed with other types of DNA repeats, including 25S rDNA sequences. Several loci containing both GRS and HRS60 were also found. Such hybrid loci may indicate intergenomic transfer of the DNA in the amphidiploidN. tabacum. GRS sequences, like HRS60 (Fajkuset al. 1992), were found to specify the location of nucleosomes. The position of the nucleosome core has been mapped with respect to a conservedMbol site in the GRS sequence and an oligo A/T tract is a major centre of the DNA curvature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00713050
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    Paper (German National Licenses)
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