Clockwise, from top left: 1) Electron density in the P4-P6 domain of Tetrahymena Group I Intron Ribozyme (J. Cate, J. Doudna, C. Kundrot, A. Gooding, T. Cech); 2) NMR structure of RNA leadzyme (P. Legault & A. Pardi); 3) X-ray structure of the lysine riboswitch (A. Garst & R. Batey); 4) NMR structure of theophylline-binding RNA (G. Zimmerman & A. Pardi); 5) X-ray structure of the dsRBD-dsRNA complex (Lingner, J., Hughes, T. R., Shevchenko, A., Mann, M., Lundblad, V. and T. Cech); 6) NMR structure of the GA3 RNA tetraloop (F. Jucker & A. Pardi)