Like other proteins that regulate gene expression, homeodomain proteins appear to be modular in nature. Regulatory target specificity is determined by the homeodomain and immediately adjacent regions while other less characterized protein domains are required for regulating gene expression. The specific aim of this proposal is to understand how protein domains outside of the homeodomain contribute to regulatory activity. The Drosophila homeotic gene Abdominal-B provides an excellent experimental system for the study of regulatory domains. Abdominal-B encodes two proteins that differ only by a glutamine rich domain, but have different genetically defined functions during development. Using a heat shock promoter system to ectopically express proteins during embryogenesis, preliminary results demonstrate that distinct segmental transformations are generated by each Abdominal-B protein, as well as a chimeric protein consisting of the Deformed protein but with a substituted Abdominal-B homeodomain. To analyze the contribution of regulatory domains to the diversity of phenotypes observed, putative regulatory domains will be altered through in vitro mutagenesis. The modified constructs will be ectopically expressed, and their effect on cuticular transformations and expression of target genes will be compared to the regulatory activity of the normal Abdominal-B proteins.
