PPIG belongs to the the peptidyl-prolyl cis/trans isomerase protein family (PPIases). PPIases accelerate the folding of proteins. PPIG 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 distributed in nuclear speckles, a nuclear compartment rich in splicing factors, and colocalizes with the splicing factors SC35 and pinin, suggesting a role in the regulation of pre-mRNA splicing.