The protein encoded by this gene is a member of the immunophilin protein family, which play a role in immunoregulation and basic cellular processes involving protein folding and trafficking. The protein may have cis-trans prolyl isomerase activity, and binds to clathrin heavy chain and heat shock protein 72. This gene is found to be deleted in Williams syndrome, and the orthologous gene in mouse is essential for fertility and homologous pairing in male meiosis.