Molecular organization of the Broad Complex of Drosophila melanogaster

The Broad-Complex (BR-C) locus of Drosophila is required for the correct progression of the steroid hormone-inducible cascade of gene expression resulting in metamorphosis. This locus is located at cytogenetic position 2B5 on the X-chromosome and spans approximately 100 kb of genomic sequence. Molecular cloning of cDNA has demonstrated that the entire 2B5 region is dedicated to the production of a family of RNAs coding for at least five related protein products. These BR-C products were shown to share a common amino-terminal region fused to one of three alternate carboxy-terminal regions. Approximately 110 residues within the common amino-terminal domain was shown to be conserved in several other known proteins by sequence comparison. Each of the carboxy-terminal regions was shown to contain a different pair of zinc finger motifs. Zinc finger motifs are responsible for the DNA binding activity of several DNA binding proteins and transcription factors. Most proteins were also shown to contain domains rich in distinctive amino acids located between the common core and zinc finger regions. The similarity of these proteins to transcription factors suggests that the BR-C directly regulates gene expression by specifying the synthesis of a family of proteins with DNA binding potential. In addition, analyses of the transcriptional start sites for BR-C messages indicated that this gene is transcribed from multiple promoters, similar to other genes known to be involved in the regulation of metamorphosis