Plays a role in pre-mRNA splicing as component of the U4/U6- U5 tri-snRNP complex that is involved in spliceosome assembly, and as component of the precatalytic spliceosome (spliceosome B complex). . This is the function of ENSG00000136875 (PRPF4, pre-mRNA splicing tri-snRNP complex factor PRPF4).