The spiceosome is a complex of RNAs and proteins that targets the splice sites in primary-mRNAs. Luhrmann and colleagues have been imaging these complexes and their sub-complexes by cryo-electron microscopy. This movie shows the 3D cryo-EM structure of the step I spliceosome as rotating wire frame representation (gold) in which the 3D structure of the 35S U5 snRNP (blue isosurface) has been docked. Video courtesy of the labs of Holger Stark and Reinhard Lührmann, Max Planck Institute. See more RNA images in the Cell Picture Show: https://www.cell.com/pictureshow/RNA