Fig. 4: The RNA path is sequentially engaged by the N-plug of DDX42, the acidic loop of DDX46 and pre-mRNA.
From: Mechanisms of the RNA helicases DDX42 and DDX46 in human U2 snRNP assembly
a The RNA path of SF3B1 is sequentially occupied by three structural motifs: the N-plug of DDX42 in DDX42-SF3b and DDX42-U2, the acidic loop of DDX46 in 17S U2, and the polypyrimidine tract (PPT) of pre-mRNA in assembled spliceosome. Shown here is a structural comparison among the relevant components from the DDX42-SF3b complex (left panel), DDX42-U2 complex (middle-left panel), 17S U2 snRNP23 (middle-right panel), and the Bact complex33. The RNA path is identified by black circles. b DDX42, DDX46 and PPT are mutually exclusive in terms of binding to the RNA path of SF3B1. Shown here is the overlay of relevant structural elements from DDX42-U2, 17S U2 and Bact complex. The alignment is made through SF3B1. c DDX42 binds to the SF3b with an apparent dissociation constant of 23 nM. Shown here are results of the bio-layer interferometry for measurement of the binding kinetics between the SF3b and DDX42 (left panel). Similarly, DDX46 binds to the SF3b with an apparent dissociation constant of 66 nM (right panel). d DDX42 and DDX46 bind SF3b in a competitive manner. Shown here are results of competition assay between DDX42 and DDX46 for binding to the SF3b core complex. DDX46 in large excess over DDX42 is able to replace DDX42 in the pre-assembled DDX42-SF3b complex, and vice versa. The assays were independently repeated for three times with similar results.
