The primary objective of the proposed study is to determine the structure and function of certain transposable genetic elements in Drosophila melanogaster. The properties of three transposable elements, 412, copia, and 297, will be investigated in detail. We will also attempt to identify and characterize additional transposable elements in the Drosophila genome. The structure of these elements, as well as the mechanism(s) and rate(s) of their transposition, will be investigated. We will use recombinant DNA techniques to isolate segments of Drosophila DNA required for this analysis. Furthermore, we will attempt to correlate the insertion and excision of these defined DNA segments with the formation and reversion of several known unstable, putative insertion mutations which have been defined genetically.