U2 small nuclear ribonucleoprotein A (SNRPA1), a 255 amino acid protein, is a component of the U2 snRNP which forms a complex with U2 snRNP B (U2B). U2 snRNP A and U2 snRNP B form together a complex which binds to the U2 snRNA hairpin IV. The configuration of the U2 snRNP A/U2 snRNP B dimer and the delicate variations of a few key residues regulate the snRNP-RNA-binding specificity.