Molecular characterization of the breakpoints of an inversion fixed between Drosophila melanogaster and D. subobscura.

The two breakpoints of a chromosomal inversion fixed since the split of Drosophila melanogaster and D. subobscura lineages have been isolated and sequenced in both species. The regions spanning the breakpoints initially were identified by the presence of two signals after interspecific in situ hybridization on polytene chromosomes. Interspecific comparison of the sequenced regions allowed us to delineate the location of the breakpoints. Close to one of these breakpoints a new transcription unit (bcn92) has been identified in both species. The inversion fixed between D. melanogaster and D. subobscura does not seem to have broken any transcription unit. Neither complete nor defective transposable elements were found in the regions encompassing the breakpoints. Short thymine-rich sequences (30-50 bp long) have been found bordering the breakpoint regions. Although alternating Pur-Pyr sequences were detected, these putative target sites for topoisomerase II were not differentially clustered in the breakpoints.