Abstract: RNA is perhaps the most functionally diverse biological macromolecule, due in large part to its ability to adopt a wide range of conformationally dynamic structures. The Kieft Lab is interested in understanding how RNA can adopt diverse three-dimensional folds, how those folds give rise to its many biological roles, and how conformational changes confer RNA’s ability to regulate so many processes. We are particularly interested in viral RNAs, which are fine-tuned by evolution to elegantly and powerfully interact with and manipulate the cellular machinery of the host cell; these viral RNAs provide a “window” into the greater RNA world. In this presentation, I will present some of our recent findings in regard to a viral RNA that adopts an unexpected tertiary structure. This RNA element undergoes programmed conformational changes that are triggered by its interactions with the host cell machinery and this is responsible for its unique function. This RNA may be a paradigm for novel modes of regulation linked to dynamic RNA conformational changes.