Binds stem loop II of U1 snRNA. It is the first snRNP to interact with pre-mRNA. This interaction is required for the subsequent binding of U2 snRNP and the U4/U6/U5 tri-snRNP. In a snRNP-free form (SF-A) may be involved in coupled pre-mRNA splicing and polyadenylation process.
[1]"Structure, chromosomal localization and evolutionary conservation of the gene encoding human U1 snRNP-specific A protein."Nelissen R.L.H., Sillekens P.T.G., Beijer R.P., Geurts van Kessel A.H.M., van Venrooij W.J.Gene 102:189-196(1991)[2