Background：

Plays a role in preventing exon skipping， ensuring the accuracy of splicing and regulating alternative splicing. Interacts with other spliceosomal components， via the RS domains， to form a bridge between the 5’- and 3’-splice site binding components， U1 snRNP and U2AF. Can stimulate binding of U1 snRNP to a 5’-splice site-containing pre-mRNA. Binds to purine-rich RNA sequences， either the octamer， 5’-RGAAGAAC-3’ (r=A or G) or the decamers， AGGACAGAGC/AGGACGAAGC. Binds preferentially to the 5’-CGAGGCG-3’ motif in vitro. Three copies of the octamer constitute a powerful splicing enhancer in vitro， the ASF/SF2 splicing enhancer (ASE) which can specifically activate ASE-dependent splicing. Isoform ASF-2 and isoform ASF-3 act as splicing repressors. May function as export adapter involved in mRNA nuclear export through the TAP/NXF1 pathway.