FK506 binding protein 3 (FKBP3), also known as FKBP25, is a member of the immunophilin protein family, which play a role in immunoregulation and basic cellular processes involving protein folding and trafficking. FKBP3 associates with transcriptional repressor protein YY1 and histone deaceltylases, HDAC1 and HDAC2. Also, FKBP3 may contain several casein kinase II phosphorylation sites, which are believed to be important for cell growth regulation. It is localized in the nucleus and is expressed in the brain, testis, ovary, and spleen. Recombinant human FKBP3 was expressed in E.coli and purified by using conventional chromatography techniques.