The studies described in this proposal will characterize the function of HoxA7 in transcriptional regulation during murine embryogenesis. Transcriptional regulatory proteins play a pivotal role in embryogenesis by controlling the expression of phenotypic target genes therefore their, characterization is crucial for understanding the molecular processes that control mammalian development. The hox genes, are master regulators of murine embryogenesis that encode putative transcriptional regulatory proteins. Many elegant biological studies have elucidated the fundamental role of hox genes during development by detailing their coordinate expression, essential function, and mode of regulation. However, many issues remained unanswered regarding the molecular mechanisms by which Hox proteins exert their action as transcriptional regulators during murine embryogenesis. The goal of this proposal is to characterize the transcriptional properties of a prototype member of the Hox family. HoxA7. HoxA7 provides an appropriate model for this analysis since it has served at a prototype for many of the original studies which have examined the expression and function of hox genes during development and since its primary sequence contains features that are reminiscent of other key transcriptional regulatory proteins. Our strategy will be to perform a detailed biochemical analysis couched within the framework of relevant biochemical systems. Our specific plans are: (I) We will characterize the molecular bases of DNA recognition by HoxA7. These studies address the mechanisms by which HoxA7 interacts selectively with DNA regulatory elements and will facilitate subsequent identification of target genes. (II) Our second goal is to characterize the transcriptional regulatory properties of HoxA7. These studies provide the framework for addressing the function of HoxA7 in the variety of distinct cell populations in which is functional during embryogenesis. (IIl) Protein factors that associate with HoxA7 will be identified and their contribution to functional specificity of HoxA7 will be evaluated. Identification of protein partners is an important step towards recapitulating functional HoxA7 protein complexes, and will provide new insight as to HoxA7 function. (IV). Finally. we will characterize the expression of HoxA7 in the developing embryo using specific polyclonal antisera that we have generated. This analysis will provide a biological context for evaluating the functional significance of the genomic target sequences, transcriptional properties, and interacting proteins factors defined in the other specific Aims. Together, these studies provide an integrated approach which will impart real insight into the function of a prototype Hox protein in transcriptional regulation during embryogenesis.