Peptidyl-prolyl cis-trans isomerase G (PPIG), also known as Cyclophilin G, is a member of peptidylprolyl cis-trans isomerase family (PPIases). This protein catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and is implicated in the folding, transport, and assembly of proteins. It is localized to the nuclear speckles, a nuclear compartment rich in splicing factors, and interacts with the splicing factors SC35 and pinin. Cyclophilin G also may play an important role in the regulation of pre-mRNA splicing.