A yeast RNA-hybrid system for the detection of RNA-RNA interactions in vivo.

RNA-RNA interactions play a crucial role at many different levels of the cellular metabolism such as plasmid replication control, viral encapsidation, or transcriptional and translational regulation. Therefore, methods are necessary to investigate the molecular determinants of given interactions, including their stabilities, or to screen for new interacting partners. We designed an RNA-hybrid system in S. cerevisiae, based on the yeast three-hybrid system. In this setup, the activation of a reporter gene is dependent on the interaction of two RNAs. A loop-loop interaction similar to the dimerization initiation site of the HIV genome was used as a model system, demonstrating that in this novel RNA-hybrid system only cognate RNAs promote the activation of the reporter gene. Levels of reporter activation correlate well with interaction stabilities determined in vitro by UV melting analyses, suggesting that conditions used for the analysis of in vitro structural stabilities translate well into the intracellular environment. Furthermore, the system was applicable for a screen against a test library. Nine out of ten selected clones were identified as predicted interaction partners for the bait RNA. In summary, we present a yeast reporter system depending on RNA-RNA interactions, which can be used alternatively for analysis of known interactions or for screening libraries in search for new interaction partners.