Fig. 6.

Models for Hb-mediated transcriptional regulation of neuroblast competence in Drosophila. Proposed molecular interactions underlying Hb function in the CNS. (A) Hb binds to its consensus sequence and recruits co-activators (and/or outcompetes repressors) to promote gene expression. (B) Hb monomers bind to genomic DNA and recruit repressor complexes. (C) Hb monomer binds to the regulatory region of a target gene, which is then repressed by dimerization with a second Hb monomer bound within a heterochromatin domain. (D) Hb dimerization is required for the recruitment of repressor complexes, which might include Mi2. Magenta ovals, Hb; smaller ovals, Hb dimerization domain; magenta squares, Hb binding sites; dark-green line, genomic DNA; green arrow, transcription start site; dark-green boxes, gene; A, activator; green square, activator binding sites; R, repressor; red squares, repressor binding sites.