Does the Promoter Constitute a Barrier in the Horizontal Transposon Transfer Process? Insight from Bari Transposons.

The contribution of the transposons' promoter in the horizontal transfer process is quite overlooked in the scientific literature. To shed light on this aspect we have mimicked the horizontal transfer process in laboratory and assayed in a wide range of hosts (fly, human, yeast and bacteria) the promoter activity of the 5' terminal sequences in Bari1 and Bari3, two Drosophila transposons belonging to the Tc1-mariner superfamily. These sequences are able to drive the transcription of a reporter gene even in distantly related organisms at least at the episomal level. By combining bioinformatics and experimental approaches, we define two distinct promoter sequences for each terminal sequence analyzed, which allow transcriptional activity in prokaryotes and eukaryotes, respectively. We propose that the Bari family of transposons, and possibly other members of the Tc1-mariner superfamily, might have evolved "blurry promoters," which have facilitated their diffusion in many living organisms through horizontal transfer.