A ribonucleoprotein complex that contains small nuclear RNA U4, a heptameric ring of Sm proteins, as well as several proteins that are unique to the U4 snRNP, most of which remain associated with the U4 snRNA both while the U4 snRNP is free or assembled into the U4/U6 snRNP or into a series of spliceosomal complexes.
snRNP U4