Transposable elements (TEs) are mobile fragments of DNA that cause DNA damage and produce harmful mutations. These genetic elements act like parasites as they spread, sometimes making up a sizeable fraction of the host genome. For example, the human genome is composed of almost 50% TEs, which are reliant on their host to spread. Due to the harmful effects associated with the movement of TEs, reducing their mobility has been the focus of extensive study. The mechanism by which host proteins help proliferate TEs in the host genome is, however, largely unknown. In particular, the host production and processing of TE DNA into RNA is critical for TE spread into the host genome. The proposed research will harness new approaches in the study of RNA regulation to identify the host cellular proteins that regulate TE RNA. The PI will also provide undergraduate and post-baccalaureate trainee opportunities and research experiences for local teachers. Target-oriented approaches allow for the systematic identification of proteins that bind, process, and regulate RNA. Particularly promising are approaches that rely on tagged RNA, which can be isolated and targeted in vivo by sequence-specific binding proteins. The proposed research will harness MS2 RNA tagging to study cellular proteins that bind to and regulate TE RNA in the genetic model Drosophila melanogaster. The research will focus on the P-element DNA transposon, which is an extensively studied model of transposition in eukaryotes