Fig. 5: SF3a120 and SF3b145 mediate interactions between U2 snRNP and tri-snRNP in the late ED pre-B and early ED B complexes.

a The interface between U2 snRNP and tri-snRNP is mediated in part by SF3a120 and SF3b145 in the late ED pre-B complex (upper panel) and early ED B complex (lower panel). SF3a120 and SF3b145 are colored salmon and violet purple, respectively. The disordered regions of these two proteins are indicated by dashed lines. The black dashed boxes, labeled accordingly, highlight the regions that are examined in detail in (b–d). b A close-up view on the interface between U2 snRNP and tri-snRNP in the late ED pre-B complex (upper panel) and early ED B complex (lower panel). Select structural elements of SF3a120 are anchored to the core region of tri-snRNP. The black dashed box highlights the region that is further examined in (c). c A close-up view on the recognition of the nucleotide A25 from U4 snRNA in the early ED B complex. This nucleotide is stabilized by SF3a120 and the NTD of PRP4. d A close-up view on the interface involving the C-terminal fragment (finger loop) of SF3b145 in the early ED B complex. The finger loop contacts the RH domain of PRP8 and the HEAT domains of PRP6 in the early ED and mature ED B complexes.