Splicing factor 1 is a protein that in humans is encoded by the SF1 gene (previously ZNF162). This protein is involved in removing introns from pre-mRNA as part of RNA splicing. In yeast, it is also frequently called Branchpoint Binding Protein (BBP), since it binds to the branch point sequence (BPS) of introns.

SF1 is a splicing factor which contributes to the formation of the major spliceosome complex. In particular, after the U2AF1-U2AF2 heterodimer binds to the 3’ end of the intron, SF1 binds to an adjacent motif in the RNA called the branch point sequence (BPS). Afterwards U2 spliceosomal RNA displaces SF1, and itself binds to the BPS.
The role of the protein in yeast cells has been the subject of study. The BPS that the protein binds to is UACUAAC.
SF1 (gene) has been shown to interact with Ewing sarcoma breakpoint region 1, U2AF2, and transcription elongation regulator 1.