Members of a new family of highly repetitive DNA sequences called GRS were isolated from Nicotiana 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 (10(4) copies per haploid genome) and could be derived from either Nicotiana tomentosiformis or Nicotiana otophora, two possible ancestors of the T genome of the amphidiploid N. tabacum. Sequence homology between the HRS60 (Koukalová et 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 amphidiploid N. tabacum. GRS sequences, like HRS60 (Fajkus et al. 1992), were found to specify the location of nucleosomes. The position of the nucleosome core has been mapped with respect to a conserved Mbol site in the GRS sequence and an oligo A/T tract is a major centre of the DNA curvature.

Institute of Biophysics of the Academy of Sciences of the Czech Republic Brno

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Three TERT genes in Nicotiana tabacum

Sequence homogenization and chromosomal localization of VicTR-B satellites differ between closely related Vicia species

Telomeres in evolution and evolution of telomeres

Dynamic changes in the distribution of a satellite homologous to intergenic 26-18S rDNA spacer in the evolution of Nicotiana

Comparative analysis of DNA methylation in tobacco heterochromatic sequences

Evidence for a sequence-directed conformation periodicity in the genomic highly repetitive DNA detectable with single-strand-specific chemical probe potassium permanganate

Species-specific evolution of telomeric and rDNA repeats in the tobacco composite genome

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