![Cartoon representation of the structure of a yeast spliceosome captured just before mRNA formation. Note how second step factors bind on the side of the complex and stabilize the position of the branch helix, thus making space for the 3’-end of the intron in the active site.](https://www2.mrc-lmb.cam.ac.uk/wordpress/wp-content/uploads/nagai-yeast-spliceosome-150x150.jpg)
The spliceosome is a molecular machine, which together with RNA polymerases and ribosomes plays a critical role in basic gene expression. Research by Kiyoshi Nagai’s group in the LMB’s Structural Studies Division, has previously revealed the structure of the spliceosome in a fully active, substrate-bound state, immediately after its first catalytic reaction. The group has now expanded upon this work revealing the near-atomic level structure of the spliceosome just before mRNA formation.