A complex repeated DNA sequence within the Drosophila transposable element copia

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Abstract
A 320 nucleotide repeated DNA sequence within the copia coding element of Drosophila melanogaster has been identified and characterized. This sequence has been localized by DNA-DNA hybridization and electron microscopic analysis of heteroduplexes to the approximate middle of the 5 kb copia coding region. The primary sequence of this repeated DNA has been determined. The sequence is composed of three related subunits, 35-37 nucleotides in length (A, B and C). This 105 nucleotide higher order repeat has apparently been duplicated twice to yield a complex repeated sequence, ABCA'B'C'A"B"C", which exhibits divergence among the individual subunits. This sequence is AT rich, as are the direct terminal repeats which flank the copia coding region, but does not contain any apparent homology with the terminal repeats. This repeated sequence contains three presumptive polyadenylation signals and two 25 nucleotide, imperfectly matched, inverted repeat sequences adjacent to two of the polyadenylation sequences.