Fig. 1: Cryo-EM structures of the DDX42-SF3b complex and the human DDX42-U2 complex.

a Mass spectrometric analyses identified peptides derived from DDX42, DDX46 and DHX15 in immunoprecipitates prepared from HEK293F cells that expressed Flag-tagged SF3B1. DDX42 and DDX46 are detected stoichiometrically with SF3B1. In contrast, the peptides of DHX15 are less abundant. b Overall structure of the DDX42-SF3b complex. The SF3b core consists of four components: SF3B1, SF3B3, SF3B5 and PHF5A. The DEAD-box ATPase/helicase DDX42 (colored in red) is bound at the periphery of the complex. c The cryo-EM map for the DDX42-U2 complex has a bi-lobal shape. The high-resolution map of the 5’ domain (colored by chain identity) is embedded in a low-pass filtered map that showing the position of the 3’ domain (left panel). The 3’ domain was modeled by docking of the previously reported coordinates (pdb: 7EVO)²³. The final model includes the SF3b complex, SF3a complex, U2 core (Sm ring, U2-A’, U2-B” and U2 snRNA), the splicing factor TAT-SF1 and the N-terminal region of DDX42 (right panel). d Docking of the atomic model of 17S U2 snRNP²³ into the low-pass filtered EM density map for the DHX15-U2 complex (colored in yellow). DDX46 (colored in purple) and TAT-SF1 (colored in orange) are present in DHX15-U2 complex; DHX15 could not be identified by the EM density map.