Repeated DNA Family Research Articles

Organization and evolution of repeated DNA sequences in closely related plant genomes

In common with many other eukaryotic species, the genomes of species in the genus Allium contain a high proportion of repeated DNA sequences, which may be implicated in the considerable differences in genome size that are seen between even very closely related species. The gross organization of repetitive sequences within the genome of Allium sativum and of some other related species has been investigated using DNA/DNA hybridization studies. Such studies show that there has been much modulation in the amounts of different repeated DNA families during the evolution of the genus Allium; these repetitive elements are interspersed in all species with sequences of low repetition. The organization and distribution of one particular repetitive family within the genus has been examined using a cloned hybridization probe. Hybridization of this probe to DNA from related genomes reveals that this element is present in all Allium species examined, but with large-scale modulation of its abundance, and some considerable changes in its sequence environment. The evolution of such genome-specific arrangements of common repetitive elements and the possible mechanisms by which they might be maintained are discussed.

Hinf family: a novel repeated DNA family of the human genome

The isolation of a mutant adenovirus carrying an insertion of cellular DNA has led to the identification of a new family of human repetitive sequences, which are found tandemly arranged in the genome. The sequence of the viral insert resembles that of eukaryotic transposable elements.

Isolation and characterization of a major tandem repeat family from the human X chromosome

We report the identification and characterization of a family of repeated restriction fragments whose molecular organization is apparently specific to the human X chromosome. This fragment, identified as an ethidium bromide-staining 2.0 kilobase (kb) band in BamHI-digested DNA from a Chinese hamster-human somatic cell hybrid containing a human X chromosome, has been cloned into pBR325 and characterized. The 2.0 kb repeated family has been assigned to the Xp11 leads to Xq12 region on the X by Southern blot analysis of somatic cell hybrids and is predominantly arranged in tandem clusters of up to seven 2.0 kb monomers. Homologous DNA sequences, not organized as 2.0 kb BamHI fragments, are found elsewhere on the X chromosome and on at least some autosomes, but are not found on the Y chromosome. From a dosing experiment using various amounts of the cloned repeat, we estimate that there are 5,000-7,500 copies of the 2.0 kb BamHI repeat per haploid genome. Since the vast majority, if not all, of these are confined to the X chromosome, this repeated DNA family must account for 5-10% of all X chromosome DNA and must constitute the major sequence component of the pericentromeric region of the X.

Ribosomal insertion-like elements in Drosophila melanogaster are interspersed with mobile sequences

Sequences homologous to the type 1 ribosomal DNA insertion occur in the chromocenter and in one location on the fourth chromosome of Drosophila melanogaster. Ribosomal insertion-like elements frequently occur in the form of tandem repeats and are often interspersed with nonhomologous DNA. Sequences that interrupt or flank insertion-like elements are members of diverged repeated DNA families. Members of five of these interspersed sequence families are located at multiple euchromatic sites as well as in the chromocenter. The euchromatic sites differ greatly in the gt-1 and gt-X11 stocks of D. melanogaster, suggesting that these sequence families are mobile in the genome. No long inverted repeats were detected in any of these interspersed sequences. One sequence, called 101F, interrupts a ribosomal insertion-like element; the nucleotide sequences across the boundaries between 101F and ribosomal insertion have been determined. A stretch of 13 base pairs that is present once in the ribosomal insertion is repeated at the ends of the 101F sequence, suggesting a target site duplication. Within the 101F element, no extended direct or inverted repeat sequence exists. The interspersed repeated sequences studied are transcribed into rare, heterogeneous, poly(A)-lacking nuclear RNA molecules. In one case, we showed that both strands of a flanking sequence are transcribed, but to a different extent. With respect to structural features and the nature of their transcripts, the sequences described here are distinct from other known transposable elements in Drosophila.