Identification of a complete P-element in the genome of Drosophila bifasciata.

A full-size P-element (IbifM3) was isolated from a genomic library of Drosophila bifasciata. The sequence has a length of 2935 bp and is flanked by 8 bp duplications of the target site. The termini are formed by 31 bp inverted repeats. The four exons have intact reading frames and possess the coding capacity for a protein of 753 amino acids and a molecular weight of 86.4 kd. The sections of the D. melanogaster transposase presumed to be functionally important (three leucine zippers and a helix turn helix motif) are conserved in the D. bifasciata P-element. Copy number and genomic distribution resemble the situation in true P-strains of D. melanogaster. Both findings support the idea that IbifM3 represents an active transposon. The sequence comparison between the P-elements of D. bifasciata, D. melanogaster and Scaptomyza pallida reveals relationships not in accordance with the phylogeny of the species. This result suggests a further case of horizontal transmission involving mobile elements in the genus Drosophila.