The aim of this proposal is to elucidate the parameters which govern gene activity and expression during differentiation and development. In order to achieve this goal it is clearly necessary to study the structure, organization as well as expression of specific genes. An ideal system of choice are the genes coding for the contractile protein actin in Drosophila melanogaster. Actin is present in nearly all cell types and is one of the most highly conserved proteins throughout evolution. It plays a number of essential roles in a given cell. While a great deal is known about the eukaryotic actin at the protein level, the knowledge about the genes coding for them is at very best minute. It does appear, however, that at least one of the actins characterized to date is developmentally regulated. Using recombinant DNA technology, hybridization kinetics, restriction enzyme/gel electrophoresis/nitrocellulose filter hybridization, direct examination of appropriate hybrids and/or heteroduplexes in the electron microscope, I will investigate the nature and organization of the actin genes, their surrounding sequences as well as the number, the nature and processing of actin mRNA's. It will be very useful in this study to isolate several actin containing recombinants and do a comparative study of these. I believe that the above studies may provide significant insights to the structural basis of the regulation of eukaryotic gene expression. Actin is a major protein responsible for structural and functional integrity of the myofibrillar apparatus. Since several genetically inherited muscular dystrophies display a disarray or degeneration of this apparatus, it is clearly important to investigate the structure and regulation of actin genes. In addition, it is conceivable that these studies will contribute to an understanding of abnormal cell growth and differentiation, i.e. cancer.