We have identified a gene complex which appears to be involved in the elaboration of positional information in Drosophila melanogaster. Based on our preliminary observations, we suggest that the decapentaplegic locus (2-4.0, 22Fl-2) is a multigene cluster controlling radial positional information within all imaginal disks. Different genes within this cluster encode different radial positional values within the disks. We have provided preliminary evidence concerning the organization of the locus, its developmental effects, a transvection position effect, and a hypermutable allele. Using our working hypothesis as a framework, we propose to initiate a multifaceted studiy aimed at understanding the molecular nature of positional information and pattern formation in this system. We will use developmental genetic, surgical and histological techniques to profile the developmental effects of decapentaplegic mutations. We will use standard Drosophila genetic techniques to look at the organization of the locus and at the effects of somatic chromosome pairing on gene expression (transvection) at decapentaplegic. Making use of some special features of our hypermutable allele, we will employ "walking" techniques to identify recombinant DNA clones containing sequences corresponding to the decapentaplegic gene. We will use these clones to study the organization of the gene complex and its transcriptional units, and to understand the molecular basis of the transvection position effect. Finally, we will attempt to identify the primary gene product(s) of this locus.