PTTG1, also known as Securin, is primarily involved in the regulation of sister chromatid separation during cell division. It has two identified roles; the first one is to help the transport of separase(cysteine protease) to the nucleus and the second role is to inhibit the catalytic activity of separase. It is ubiquitinated by the Anaphase Promoting Complex (APC), and then degraded by the Proteasome, releasing separase.