Complete nucleotide sequence of the Drosophila transposable element copia: homology between copia and retroviral proteins.

We have determined the complete nucleotide sequence of the copia element present at the white-apricot allele of the white locus in Drosophila melanogaster. This transposable element is 5,146 nucleotides long and contains a single long open reading frame of 4,227 nucleotides. Analysis of the coding potential of the large open reading frame, which appears to encode a polyprotein, revealed weak homology to a number of retroviral proteins, including a protease, nucleic acid-binding protein, and reverse transcriptase. Better homology existed between another part of the copia open reading frame and a region of the retroviral pol gene recently shown to be distinct from reverse transcriptase and required for the integration of circular DNA forms of the retroviral genome to form proviruses. Comparison of the copia sequence with those of the Saccharomyces cerevisiae transposable element Ty, several vertebrate retroviruses, and the D. melanogaster copia-like element 17.6 showed that Ty was most similar to copia, sharing amino acid sequence homology and organizational features not found in the other genetic elements.