To understand the mechanisms of gene expression in higher organisms we are studying two sets of coordinated gene responses in Drosophila: 1) the production of muscle-specific proteins in myogenesis and 2) the "heat shock" response induced in both eukaryotic and prokaryotic cells by a variety of environmental stresses. Both of these phenomena are useful experimental systems for study of the kinds of genetic activity that occur during differentiation in eukaryotes. In addition, myogenic differentiation is an important developmental process in its own right and the heat shock response is perhaps the most fundamental mechanism by which cells of all organisms achieve homeostasis at times of environmental stress. Our studies on heat shock genes will focus on the hsrw locus. We have shown that this locus is very different from other heat shock loci and, in fact, from any other known gene. Our results suggest that the hsrw locus plays a general regulatory role in both stressed and non-stressed Drosophila cells. We hypothesize that the omega1 transcript acts to sequester a nuclear factor and that the omega3 transcript plays a role in the translational process. Experiments to teat these hypotheses about hsrw function are proposed. If hsrw has the role we suggest, it is likely that other eukaryotes will have equivalent loci and that understanding the Drosophila gene will allow us to identify these loci in other species. Experiments have been designed to search for hsrw loci outside the genus Drosophila. Our studies on muscle will focus in two areas: 1) Studies of the Z-band, the myofibrillar component that anchors thin filaments and transmits tension from one sarcomere to the next. We now have monoclonal antibodies that identify four major high molecular weight Z-band components; these antibodies are being used to clone the corresponding genes from expression libraries. We propose to obtain a complete collection of Z-band antibodies and cloned genes from expression libraries. We propose to obtain a complete collection of Z-band antibodies and cloned genes and to use these probes to analyze the structure and assembly of this myofibrillar structure; 2) proteins of thick and thin filaments. Our studies have identified several Drosophila myofibrillar proteins which seem to have novel functions. Two that we are studying are interesting because of their distribution in Drosophila muscle. The first is mp20, which appears specific for the synchronous muscle. The second (a cluster of three isoforms) is found only in asynchronous muscle. Both proteins localize to the A-band. One possibility is that the muscle-type restriction of our proteins indicates a role in the contraction or relaxation process in that muscle-type; further studies on the proteins may give insight into the mechanisms involved. We propose molecular and genetic studies on these proteins and the corresponding genes.