Involved in pre-mRNA splicing as component of the spliceosome (PubMed:11991638, PubMed:28076346). Combines RNA-binding and PPIase activities (PubMed:18258190, PubMed:20460131, PubMed:20677832, PubMed:8977107). Binds mRNA and has a preference for single-stranded RNA molecules with poly-A and poly-U stretches, suggesting it binds to the poly(A)-region in the 3'-UTR of mRNA molecules (PubMed:18258190, PubMed:20460131, PubMed:8977107). Catalyzes the cis-trans isomerization of proline imidic peptide bonds in proteins (PubMed:18258190, PubMed:20541251, PubMed:20677832, PubMed:8977107). Inhibits KMT2A activity; this requires proline isomerase activity (PubMed:20460131, PubMed:20541251, PubMed:20677832). {ECO:0000269|PubMed:11991638, ECO:0000269|PubMed:18258190, ECO:0000269|PubMed:20460131, ECO:0000269|PubMed:20541251, ECO:0000269|PubMed:20677832, ECO:0000269|PubMed:28076346, ECO:0000269|PubMed:8977107}. This is the function of PPIE (peptidylprolyl isomerase E, ENSG00000084072).