Binds to the catalytic subunit of the cyclin dependent kinases and is essential for their biological function (By similarity). Has a role in the exit from M phase during early mitotic cell division. More specifically, thought to act by degrading B-type cyclins that causes breakdown of nuclear envelope and exit mitosis. Forms a homohexamer that can probably bind six kinase subunits (By similarity). Interacts with cdk-1. Worms exhibit defects in the completion of maternal meiosis, embryonic mitosis and arrest in embryogenesis. Belongs to the CKS family.