| Popis: |
Homeotic genes of Drosophila determine the unique development of each segment and must be precisely regulated to ensure normal development. Long-term maintenance of homeotic gene expression requires the presence of positive (trithorax-Group) and negative (Polycomb-Group) regulators. Trithorax (trx) is the prototypic member of the trithorax-Group and is required for the positive maintenance of homeotic gene expression patterns. We developed two different polyclonal antibodies against parts of trx proteins. Using these antibodies we showed that the trx proteins bind to 63 specific sites on the polytene chromosomes of larval salivary glands. These sites include sites of their known targets, the Bithorax and Antennapedia complexes. Binding of trx to the cytological location of the Bithorax complex, which is not expressed in salivary glands, suggests that the trx binding is constitutive. We localized one trx binding site within a 670 bp fragment of the 5′ regulatory region of Ultrabithorax (Ubx). These results suggest that the trx proteins exert their effect by binding directly or indirectly to specific DNA sequences in their target genes. We showed that the trx proteins co-localize with Polycomb-Group proteins at many sites on the polytene chromosomes. The same DNA fragment from the Ubx regulatory region also contains binding sites for Polycomb-Group proteins. Our results also indicate that the trx proteins are co-localized at almost all sites with another member of the trithorax-Group proteins, the absent, small, homeotic 1 protein. These results suggest that the interaction between these positive and negative regulators of the homeotic genes may be important for their mode of action. The trx proteins contain a DNA-binding motif which is a novel variant of the DNA-binding domains of the nuclear receptor superfamily. We expressed this domain as a fusion protein and used an electrophoretic mobility shift assay to investigate and characterize its DNA-binding activity |
