Serine/arginine-rich splicing factor 1, also known as SFRS1, is a member of the arginine/serine-rich splicing factor protein family, and functions in both constitutive and alternative pre-mRNA splicing. This protein binds to pre-mRNA transcripts and components of the spliceosome, and can either activate or repress splicing depending on the location of the pre-mRNA binding site. The protein's ability to activate splicing is regulated by phosphorylation and interactions with other splicing factor associated proteins. Recombinant human SFRS1 protein, fused to His-tag at N-terminus, was expressed in E.coli.