Study of the enhancer-blocking activities of new boundaries in the bithorax complex of Drosophila melanogaster

It was shown earlier that the Mcp, Fab-7, and Fab-8 boundaries of the bithorax complex contain insulators that effectively block the enhancers of the yellow and white genes. Other boundaries have not been studied so far. The recent mapping of binding sites for the insulator protein dCTCF in the regulatory regions of the bithorax complex genes permitted the Fab-3, Fab-4, and Fab-6 boundaries to be localized. Here, we showed that, despite the presence of dCTCF-binding sites, fragments of the Fab-3, Fab-4, and Fab-6 boundaries do not exhibit the properties of insulators in the model system with the yellow and white genes. Moreover, in some regions of the genome the Fab-4 and Fab-6 boundaries display the properties of silencers.