LAUSR

Recent cryo‐EM structures of a group II intron caught in the process of invading DNA have given new insight into the mechanisms of both splicing and retrotransposition. Conformational dynamics involving the branch‐site helix domain VI are responsible for substrate exchange between the two steps of splicing. These structural rearrangements have strong parallels with the movement of the branch‐site helix in the spliceosome during catalysis. This is strong evidence for the spliceosome evolving from a group II intron ancestor. We observe other topological changes in the overall structure of the catalytic domain V that may occur in the spliceosome as well. Therefore, studying group II introns not only provides us with insight into the evolutionary origins of the spliceosome, but also may inform the design of experiments to further probe structure–function relationships in this eukaryotic splicing apparatus.