Processes such as embryonic development, cell differentiation or adaptation of cells to environmental conditions all involve changes in the levels of expression of various genes. Our knowledge of such processes will necessarily remain superficial as long as we do not understand the mechanisms by which cells control the activities of their individual genes. I propose to study the mechanism of regulation of Drosophila heat-shock gene expression at the molecular level. In drosophila embryonic cells or in larvae these genes are essentially eilent at 25 degrees but are transcribed and translated at exceedingly high rates at 35-37 degrees C into a small number of polypeptides with characteristic molecular weights. The same genes are also activated by amino acic analogs and by various metabolic inhibitors. Heat-shock genes coding for proteins for similar structures have been found in cells from a variety of eucaryotic organisms. Human cells produce large amounts of heat-shock proteins at 41 degrees C but not at 37 degrees C. This observation suggests that the regulation of heat-shock gene expression represents an important aspect of biochemistry of organisms during periods of fever or during hyperthermic tratments (used with some success in cancer therapy). The Drosophila heat-shock genes appear to be ideal for studies of mechanisms of gene activation because (1) they represent a clear-cut case of regulation at the transcriptional level, (2) all seven major heat-shock protein genes have been isolated and the DNA sequences of most of these genes and of the regions flanking them have been determined and (3) our preliminary experiments have shown that a cloned Drosophila heat-shock gene is transcribed correctly in heat-treated but not in untreated Xenopus oocytes. Thus the Xenopus oocyte system can be employed as a fast and convenient assay for studying the heat-induced expression of isolated heat-shock genes. By using this experimental system I will attempt to (1) identify the DNA sequences important for the heat-activation and the correct transcription of Drosophila heat-shock genes and (2) define and eventually purify (RNA/protein) components of the regulatory system. Sets of mutant genes will be prepared by in vitro DNA sequence manipulation, and their heat-controled experesion will be studied by the oocyte assay. The regulatory effects of lysates and lysate fractions prepared from heat-treated or untreated Drosophila cells on transcription of Drosophila heat-shock genes will be examined by injection of such lysates into Xenopus oocytes carrying Drosophila heat-shock genes. This way I hope to identify elements of the Drosophila heat-shock gene control system.