Isoform 1 is involved as a ribosomal RNA processing factor in ribosome biogenesis. Binds to tightly bent AT-rich stretches of double- stranded DNA. . Isoform 2 binds to double-stranded DNA. . This is the function of PIN4 (peptidylprolyl cis/trans isomerase, NIMA-interacting 4, Ensembl gene identifier ENSG00000102309).