BTB/POZ domain-containing protein KCTD5 (KCTD5), is a 234 amino acid protein which localizes mainly in the cytoplasm however translocates to the nucleus on interaction with REP proteins. The expression of KCTD5 is up regulated post-transcriptionally in peripheral blood lymphocytes stimulated via the T-cell receptor. KCTD5 interacts particularly with cullin3, attaches ubiquitinated proteins, and created oligomers through its BTB domain.