Co-expression of RNA–protein complexes in Escherichia coli and applications to RNA biology

RNA has emerged as a major player in many cellular processes. Understanding these processes at the molecular level requires homogeneous RNA samples for structural, biochemical and pharmaco-logical studies. We previously devised a generic approach that allows efficient in vivo expression of recombinant RNA in Escherichia coli. In this work, we have extended this method to RNA/ protein co-expression. We have engineered several plasmids that allow overexpression of RNA–protein complexes in E. coli. We have investigated the po-tential of these tools in many applications, including the production of nuclease-sensitive RNAs encap-sulated in viral protein pseudo-particles, the co-production of non-coding RNAs with chaperone proteins, the incorporation of a post-transcriptional RNA modification by co-production with the appro-priate modifying enzyme and finally the production and purification of an RNA–His-tagged protein complex by nickel affinity chromatography. We show that this last application easily provides pure material for crystallographic studies. The new tools we report will pave the way to large-scale structural and molecular investigations of RNA function and interactions with proteins