Protein associated with the U5 snRNP, during its maturation and its post-splicing recycling and which is required for spliceosomal tri-snRNP complex assembly in the nucleus (PubMed:34131137, PubMed:35188580). Has a molecular sequestering activity and transiently hinders SNRNP200 binding sites for constitutive splicing factors that intervene later during the assembly of the spliceosome and splicing (PubMed:35188580). Together with its molecular sequestering activity, may also function as a molecular adapter and placeholder, coordinating the assembly of the U5 snRNP and its association with the U4/U6 di-snRNP (PubMed:34131137).
