Genomic environment influences the dynamics of the tirant LTR retrotransposon in Drosophila.

Combining genome sequence analysis and functional analysis, we show that some full-length copies of tirant are present in heterochromatic regions in Drosophila simulans and that when tested in vitro, these copies have a functional promoter. However, when inserted in heterochromatic regions, tirant copies are inactive in vivo, and only transcription of euchromatic copies can be detected. Thus, our data indicate that the localization of the element is a hallmark of its activity in vivo and raise the question of genomic invasions by transposable elements and the importance of their genomic integration sites.