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 o f Drosophila melanogaster and D. subobscura lineages have been isolate d and sequenced in both species. The regions spanning the breakpoints initially were identified by the presence of two signals after intersp ecific in situ hybridization on polytene chromosomes. Interspecific co mparison of the sequenced regions allowed us to delineate the location of the breakpoints. Close to one of these breakpoints a new transcrip tion unit (bcn92) has been identified in both species. The inversion f ixed between D. melanogaster and D. subobscura does not seem to have b roken any transcription unit. Neither complete nor defective transposa ble elements were found in the regions encompassing the breakpoints. S hort thymine-rich sequences (30-50 bp long) have been found bordering the breakpoint regions. Although alternating Pur-Pyr sequences were de tected, these putative target sites for topoisomerase II were not diff erentially clustered in the breakpoints.