Fig. 3
From: Structures of the human spliceosomes before and after release of the ligated exon
Structural rearrangements during the P-to-ILS1 transition. a Overall structural changes during the P-to-ILS1 transition. All RNA elements are shown. The protein components that remain unchanged are not shown. SRm300 is shown in a surface representation. EJC exon junction complex. b Conformational changes of Prp8 during release of the ligated exon. During the P-to-ILS1 transition, the step II factor Slu7 and SRm300 is dissociated and the Switch loop that binds SRm300 is flipped by about 180 degrees. The RNaseH-like domain (colored wheat) and the 3′SS are moved away from the active site in the P complex. c A cartoon diagram for the release of ligated exon. Driven by Prp22-mediated pulling, the β-finger (colored cyan) of the RNaseH-like domain is unbolted from the active site of the P complex; the Switch loop along with SRm300 and the 5′-exon are rotated 180°, releasing the ligated exon through the tunnel formed by RNaseH-like, the Linker/Endo and N-domain of Prp8. In the P complex, the 1585-loop binds the 3′SS next to the exon junction, and this interaction must be disrupted prior to the release of the ligated exon. The 3′SS is flipped out of the catalytic center and becomes flexible during this process. The putative gate of exon release between intron lariat and four domains of Prp8 is marked by black dotted lines in the ILS1 complex
