Involved in pre-mRNA splicing as component of the spliceosome (PubMed:11991638, PubMed:28076346). Combines RNA-binding and PPIase activities (PubMed:8977107, PubMed:18258190, PubMed:20677832, PubMed:20460131). 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:8977107, PubMed:18258190, PubMed:20460131). Catalyzes the cis-trans isomerization of proline imidic peptide bonds in proteins (PubMed:8977107, PubMed:18258190, PubMed:20677832, PubMed:20541251). Inhibits KMT2A activity; this requires proline isomerase activity (PubMed:20677832, PubMed:20541251, PubMed:20460131). [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Enzyme activity is inhibited by cyclosporin A. Identified in the spliceosome C complex (PubMed:11991638, PubMed:28076346). Component of the XAB2 complex, a multimeric protein complex composed of XAB2, PRPF19, AQR, ZNF830, ISY1, and PPIE (PubMed:17981804). Identified in a pentameric intron-binding (IB) complex composed of AQR, XAB2, ISY1, ZNF830 and PPIE that is incorporated into the spliceosome as a preassembled complex (PubMed:25599396). The IB complex does not contain PRPF19 (PubMed:25599396). Interacts (via RNA-binding domain) with KMT2A (via the third PHD-type zinc-finger) (PubMed:20677832, PubMed:20541251, PubMed:20460131). Found in all the examined tissues including heart, brain, placenta, lung, liver, skeletal muscle, kidney and pancreas. The RRM domain mediates both interaction with RNA and with KMT2A (via the third PHD-type zinc-finger), but has much higher affinity for the KMT2A PHD-type zinc-finger. Belongs to the cyclophilin-type PPIase family. PPIase E subfamily.