Rearrangements within the U6 snRNA Core during the Transition between the Two Catalytic Steps of Splicing (Molecular Cell)

Cryo-EM structures of catalytic spliceosomes depict the snRNA catalytic core in the same, unchanged conformation. Eysmont et al. show that U6-ISL within the catalytic core toggles between catalytic and non-catalytic conformations due to flexibility within the lower ISL segment. Changes of relative stabilities of these conformations affect splicing fidelity.