Peptidyl-Prolyl Cis-Trans Isomerase H (PPIH) belongs to the Cyclophilin-type PPIase family that accelerate the folding of proteins. PPIases can catalyze the cis-trans isomerization of Proline Imidic peptide bonds in oligopeptides. PPIH participates in pre-mRNA splicing. It is a specific component of the complex that includes pre-mRNA processing factors PRPF3, PRPF4, and PRPF18, as well as U4/U5/U6 tri-snRNP. In addition, PPIH has PPIase activity and may play a role as a chaperone mediating the interactions between different proteins inside the spliceosome.