Project Abstract The project seeks to understand the function of the cis-regulatory sequences that control animal development, using the embryo of the pomace fly Drosophila melanogaster as a model system. Given the importance of gene regulation in virtually every facet of biology, including many human diseases, it is remarkable how poorly we understand the relationship between the base sequence of the genomic regions that control transcription and their function. Despite a growing catalog of well-characterized regulatory sequences from numerous species, especially D. melanogaster, we still can not reliably recognize regulatory sequences in DNA, determine the expression pattern of a gene from the sequences that surround it, predict the consequences of variation in regulatory sequences, or design regulatory sequences de novo to produce a desired pattern of expression. The early D. melanogaster embryo has long been a model for the study of transcriptional regulation. During the first several hours of its development, the D. melanogaster embryo transforms a small number of crude spatial cues left behind by its mother into intricate spatial patterns of expression of thousands of genes that establish the body plan and tissue identities of the embryo, larvae and adult fly. Technological advances in the last decade have enabled the generation of an increasingly detailed portrait of this regulatory network and the molecular events that underlie it, as well as genome sequences of D. melanogaster and many of its genetic variants and sister species. The central premise of this proposal is that we can infer from these data the molecular logic of gene regulation. In particular, we propose to model three aspects of this system: 1) the manner in which regulatory information is distributed across the D. melanogaster genome, 2) constraints on the evolution of regulatory sequences, and 3) the detailed relationship between DNA sequence and gene expression. Each of these models will reveal not only details of the D. melanogaster regulatory network, but will also illuminate the biophysical and logical principles that unite gene regulation in all animals, including humans.