U4 small nuclear RNA (U4 snRNA) is a component of the major U2-dependent spliceosome. It forms a duplex with U6, and with each splicing round, it is displaced from U6 (and the spliceosome) in an ATP-dependent manner, allowing U6 to refold and create the active site for splicing catalysis. A recycling process involving protein Prp24 re-anneals U4 and U6.