The family Filoviridae consists of the Ebola and Marburg viruses. Infections with these hemorrhagic fever viruses results in massive bleeding into the gastrointestinal tract as well as hemorrhages from puncture wounds and mucus membranes. The high mortality rate and unresolved mode of infection, coupled with the lack of effective vaccine or antivirals, have resulted in these viruses being classified in a Category A by the Center for Disease Control. The potential for the use of these viruses as bio-weapons necessitates the continued design, synthesis, and evaluation of new therapeutic strategies. Filoviruses are negative stranded RNA viruses. The major features of the viral replication cycle have been elucidated. After the virus enters the cell and uncoats, the negative strand genome RNA serves as a template for the synthesis of mRNAs. Ebola and Marburg viruses each encode seven viral proteins translated from individual mRNAs. Each of the seven mRNAs contains an RNA stem-loop at the 5' end of the mRNA. Disruption of this RNA stem-loop would be expected to effect both on the expression of viral proteins and replication. Thus, the RNA stem-loops represent excellent targets for the development of RNA binding ligands designed to inhibit virus gene expression and replication. The long-term goal of the proposed experiments is to develop new therapeutic strategies for intervention of Filovirus infections. To do this, we propose to first develop ligands that bind to the RNA stem-loops to inhibit gene expression. The following Specific Aims are proposed: Specific Aim 1: To identify RNA and protein ligands that bind to RNA stem-loops of Ebola and Marburg virus RNAs. Specific Aim 2: To determine the capacity of peptide and protein ligands to block translation of mRNAs with the Ebola and Marburg RNA stem loops. The results of these studies will establish the importance of the RNA stem-loops and provide the foundation for development of new therapeutics designated to disrupt both Ebola and Marburg virus replication.