Fig. 1
From: Structures of the human pre-catalytic spliceosome and its precursor spliceosome
Cryo-EM structures of the human precursor pre-catalytic spliceosome (the pre-B complex) and the pre-catalytic spliceosome (the B complex). a Structures of the pre-B complex (left panel) and the B complex (right panel). The protein and RNA components are color-coded and tabulated below the images. The pre-B complex, but not the B complex, contains Sad1, Prp28, and U1 snRNP. Components of U1 snRNP (colored grey) remain unassigned due to the low resolution of the EM density map in this region. Compared to pre-B, the B complex has eight additional protein components: CypH, FBP21, MFAP1, Prp38, Smu1, Snu23, Snu66, and UBL5. Although the U4/U6.U5 tri-snRNP is the core in both complexes, it undergoes pronounced structural rearrangement. b Structures of the RNA elements in the pre-B complex (left panel) and the B complex (right panel). The pre-mRNA, U2, U5, and U6 snRNAs are colored red, marine, orange, and green, respectively. This color scheme is preserved throughout this manuscript. In the pre-B complex, the BPS is already recognized by complementary sequences of U2 snRNA through duplex formation, and the 3’-end sequences of U6 snRNA forms helix II with the 5’-end sequences of U2 snRNA. The 5’-exon of the pre-mRNA is anchored to loop I of U5 snRNA in the B complex, but not the pre-B complex. All structural images were created using PyMol68
