Much of our basic knowledge about RNA metabolism has come from the study of viruses. In our laboratory, we are interested in the genomic RNA structures and replication machinery of RNA viruses, particularly Hepatitis C Virus (HCV). This work is linked to our study of RNA helicase enzymes, which are critical for many viral functions. Viral RNA helicases are important drug targets for the development of therapeutics and they are particularly useful model systems for the study of complex molecular machines because they typically have more than one function in the virus. Thus, viral helicases like HCV NS3 are often multifunctional proteins with elaborate appended domains and partner proteins that regulate and attenuate catalytic function. In our laboratory, we study the regulation of helicase function, the interactions with partner proteins, and the detailed molecular motions that are essential for helicase function in the context of a virus. Our kinetic and molecular studies are complemented by collaborative studies of viral behavior in vivo. In this way, we hope to build a mechanistically detailed, biologically relevant understanding of helicase motor function in the lifecycle of RNA viruses.