The long term objective of this research is to determine how coordinated programs of gene expression direct development in eukaryotes. The first phase of this work is proposed here and focuses on a molecular investigation of the structure and function of 3 interrelated and coordinated gene sets which affect the development of larval salivary glands in Drosophila. The steroid hormone beta-ecdysone represses transcription of the previously active intermolt gene while simultaneously inducing a new gene set - the early acdysone-induced genes. The late acdysone-induced gene set becomes active after and probably requires the expression of the early gene set. Recombinant DNA techniques will be used to isolate and molecularly characterize cloned genomic DNA segments (Dm-segments) which contain 1 or 2 model genes of each set. These Dm-segments will be compared to others which represent the remaining members of the gene set to test whether common regulatory DNA sequence elements are present throughout the set. Further experiments will examine genes of different sets for common elements (for example, ecdysone-receptor binding sites). Additional experiments will be directed at the biochemical characterization of early gene products hypothesized to be the intermediate regulatory molecules in the delayed and coordinated expression of the late genes. Several known and previously mapped mutations which apparently affect the expression and/or regulation of early and late gene sets will be investigated.