3372 Nucleic Acids Research, 2011, Vol. 39, No. 8 ACKNOWLEDGEMENTS The authors thank Ronald Micura, Ulrike Rieder and Renee Schroeder for fruitful discussions. The authors are grateful to Joachim W. Engels and Renee Schroeder for the opportunity to measure melting curves and Olga Frolow and Sabine Stampﬂ for the kind introduction to the instruments. FUNDING Aventis Foundation; the Deutsche Forschungsgemeinschaft (DFG: Cluster of Excellence: Macromolecular Complexes and SU 402/4-1 to B.S., WO 901/2-1 to J.W.); Volkswagenstiftung; Center of Biomolecular Magnetic Resonance (BMRZ); Johann Wolfgang Goethe-University Frankfurt and Heisenberg stipend of the DFG (HA 3459/5) to C.H. Funding for open access charge: DFG. Conﬂict of interest statement. None declared. REFERENCES 1. Roth,A. and Breaker,R.R. (2009) The structural and functional diversity of metabolite-binding riboswitches. Annu. Rev. Biochem., 78, 305–334. 2. Suess,B. and Weigand,J.E. 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