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). {ECO:0000269|PubMed:26912367, ECO:0000269|PubMed:28781166, ECO:0000305|PubMed:20595234}. This is the function of Ensembl gene identifier ENSG00000117360 (PRPF3, pre-mRNA processing factor 3).