Interdigitated arrangement of two oligo(A)-terminated DNA sequences inDrosophila

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Abstract
A cluster of repeated sequences composed of three distinguishable units has been Isolated from Drosophila melanogaster, and characterized. The region, cloned as pDnl 158, contains a segment that 1s homologous to the type 1 Hbosomai Insertions, a member of the F family of transposable sequences, and a newly described repeated sequence that we have named 6. F elements are transposable sequences that lack terminal repeats, generate target site duplications at the point of Insertion, and contain an oligo(A) stretch at one end. 6 sequences are structurally similar though non-homologous to F 1n that they also carry an o11go(A) stretch. The structure of the 158 region of the genome 1s best explained by assuming three consecutive events. An F element did Insert Into a Hbosonal Insertion-like sequence, followed by the Introduction of a 6 sequence Into F. Subsequently, a DNA segment comprising a portion of G and F was tandemly triplicated to yield the arrangement observed. The nested Interspersion of repeated sequence elements may be a corantm feature of eukaryotic genomes.