InterPro domain: IPR032570

This helix-hairpin domain can be found in N-terminal region of mammalian splicing factor 1 (SF1) and fungal branchpoint binding proteins (BBP) [ 1 ]. These proteins are required for pre-spliceosome formation, which is the first step of pre-mRNA splicing [ 2 , 3 ].

SF1 forms a complex with U2AF65 through the interaction between this domain and the C-terminal U2AF homology motif domain (UHM) of U2AF65. This domain forms a secondary, hydrophobic interface with U2AF65(UHM) to lock the orientation of the two subunits, which is essential for cooperative formation of the ternary SF1-U2AF65-RNA complex [ 4 ]. This domain contains a highly conserved SPSP motif at its C terminus; the phophorylation of the SPSP motif induces a disorder-to-order transition within a novel SF1/U2AF65 interface [ 5 ].

1. STAR, a gene family involved in signal transduction and activation of RNA. Trends Genet. 19, 1873-86
2. Pre-spliceosome formation in S.pombe requires a stable complex of SF1-U2AF(59)-U2AF(23). EMBO J.
3. A dual role for BBP/ScSF1 in nuclear pre-mRNA retention and splicing. EMBO J.
4. Structure, phosphorylation and U2AF65 binding of the N-terminal domain of splicing factor 1 during 3'-splice site recognition. Nucleic Acids Res. 13, 479-84
5. Structure of Phosphorylated SF1 Bound to U2AF(65) in an Essential Splicing Factor Complex. Structure 21, 5516-26