SF1 (splicing factor 1) is a critical RNA-binding protein that facilitates the ATP-dependent first step of spliceosome assembly during pre-mRNA splicing 1. The protein specifically binds to the intron branch point sequence 5'-UACUAAC-3' of pre-mRNA and interacts transiently with the SURP1 domain of the U2 snRNP component SF3A1, with a dissociation constant of approximately 20 μM, indicating a weak but functionally important interaction 1. This transient binding facilitates recruitment of U2 snRNP to early spliceosomal complexes, from which SF1 is subsequently dissociated during complex conversion 1. As a member of the SF1 helicase superfamily, SF1 shares structural similarity with other helicases involved in RNA and DNA metabolism, possessing characteristic RecA-like domains essential for its enzymatic activity 23. Beyond its splicing function, SF1 may also act as a transcription repressor. The protein localizes to the nucleoplasm and nucleus, where it participates in mRNA cis splicing via the spliceosome and contributes to 3'-splice site recognition [GO annotations]. While specific disease associations for the splicing factor SF1 are not detailed in the provided abstracts, its fundamental role in pre-mRNA processing makes it essential for proper gene expression regulation.