Transposable elements controlling I-R hybrid dysgenesis in D. melanogaster are similar to mammalian LINEs

Abstract

I-R hybrid dysgenesis in D. melanogaster is controlled by transposable elements known as I factors. We have determined the base sequences of one complete I factor and the ends of six others. The ends of these elements are highly conserved and are flanked by target site duplications varying in length from 10–14 bp. There are no terminal repeats, and the 3′ end of one strand is A-rich, having 4–7 tandem repeats of the sequence TAA. This sequence organization is similar to that of mammalian LINEs, or L1 elements. The complete I factor sequence contains two long open reading frames, ORF1 and ORF2, of 1278 and 3258 bp. ORF1 encodes a possible nucleic acid-binding protein, and part of the amino acid sequence of ORF2 is similar to that of viral reverse transcriptases and polypeptides encoded by L1 elements. These results suggest that I factors transpose by reverse transcription of a full-length RNA.