Fig. 6
From: Structures of the human pre-catalytic spliceosome and its precursor spliceosome
Structural rearrangement from the human U4/U6.U5 tri-snRNP to the human pre-B and B complexes. a Comparison of the structures between the human U4/U6.U5 tri-snRNP13 (left panel) and the human pre-B complex (right panel). U1 and U2 snRNPs have been recruited into the pre-B complex. b Comparison of the EM density maps reveals global differences among the tri-snRNP (left panels), the pre-B complex (middle panels), and the B complex (right panels). These three complexes are oriented identically with respect to the core components of the U4/U6.U5 tri-snRNP. Compared to the tri-snRNP, the human pre-B complex contains two additional large lobes of EM density: one assigned to U1 snRNP and the other to U2 snRNP. The heptameric LSm ring undergoes a positional shift from the tri-snRNP to the pre-B complex. Compared to the pre-B complex (middle panels), the EM density lobe assigned to U1 snRNP is absent in the B complex (right panels). The EM density for U2 snRNP and U6 LSm ring exhibits apparent differences. c A cartoon diagram of the human pre-B-to-B transition trigged by the RNA-dependent ATPase/helicase Prp28. One of the most notable changes in this transition is the engagement of pre-mRNA by both U5 and U6 snRNA
