Required for pre-mRNA splicing and maintenance of stable U6 small nuclear RNA levels. Implicated in the formation of stable and biologically active snRNP structures. As part of the U4/U6.U5 tri-snRNP particle, dispensible for spliceosome assembly, but required for conformational changes, which result in U4 snRNA release and the subsequent catalytic activation of the spliceosome (By similarity). Component of the 25S U4/U6.U5 tri-snRNP particle, a subcomplex of the spliceosome. Belongs to the PRP38 family.