This family consists of several eukaryotic splicing factor 3B subunit 1 proteins, which associate with p14 through a C-terminus beta-strand that interacts with beta-3 of the p14 RNA recognition motif (RRM) beta-sheet, which is in turn connected to an alpha-helix by a loop that makes extensive contacts with both the shorter C-terminal helix and RRM of p14. This subunit is required for 'A' splicing complex assembly (formed by the stable binding of U2 snRNP to the branchpoint sequence in pre-mRNA) and 'E' splicing complex assembly [1].

1: Crystal structure of a core spliceosomal protein interface. Schellenberg MJ, Edwards RA, Ritchie DB, Kent OA, Golas MM, Stark H, Luhrmann R, Glover JN, MacMillan AM; Proc Natl Acad Sci U S A. 2006;103:1266-1271. PMID:16432215