PPIases accelerate the folding of proteins. It catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides. May be implicated in the folding, transport, and assembly of proteins. Probably involved in early steps of spliceosomal assembly. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Interacts with SNRNP35, RNU1, SCL28, SCL30, SR30 and SR34. The binding to SR34 is phosphorylation-dependent (PubMed:15166240). Moves from nuclear bodies to nuclear speckles upon interaction with SR proteins. Ubiquitous. Belongs to the cyclophilin-type PPIase family.