PPIG belongs to a highly conserved class of cyclophilins that function as peptidyl-prolyl-isomerases to catalyze the conversion of cis-proline to trans-proline in a polypeptide chain. PPIG contains an amino-terminal cyclophilin domain followed by Nopp140 repeats that are involved in its function as a nuclear chaperone. The carboxy-terminal of PPIG contains a SR domain that is involved in pre-mRNA splicing and processing. PPIG interacts with the carboxy-terminal domain of RNA polymerase II as well as several other SR family splicing factors. These interactions lead to changes in localization and conformation and suggest a regulatory role in transcription and pre-mRNA splicing in the elongating RNA polymerase complex. PPIG is found in the nuclear matrix and nuclear speckles and is involved in the regulation of gene expression. PPIG shows a predominantly diffuse cytoplasmic distribution at the onset of mitosis, and in late telophase the isomerase is recruited to the newly formed nuclei.
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