CONSTITUTIVE HETEROCHROMATIN AND TRANSPOSABLE ELEMENTS IN DROSOPHILA-MELANOGASTER

Several families of transposable elements (TEs), most of them belongin g to the retrotransposon category, are particularly enriched in Drosop hila melanogaster constitutive heterochromatin. The enrichment of TE-h omologous sequences into heterochromatin is not a peculiar feature of the Drosophila genome, but appears to be widespread among higher eukar yotes. The constitutive heterochromatin of D. melanogaster contains se veral genetically active domains; this raises the possibility that TE- homologous sequences inserted into functional heterochromatin compartm ents may be expressed. In this review I present available data on the genetic and molecular organization of D. melanogaster constitutive het erochromatin and its relationship with transposable elements. The impl ications of these findings on the possible impact of heterochromatic T Es on the function and evolution of the host genome are also discussed .