PBK(PDZ-binding kinase) is also named as TOPK, CT84, Nori-3, SPK and belongs to the MAP kinase kinase subfamily. PBK may have a role in the regulation of cellular proliferation and progression of the cell cycle. It has a characteristic cdc2ycyclin B phosphorylation site(SyT-P-X-KyR) at its N terminus,which is conserved across species, and it is phosphorylated in a cell cycle-dependent manner at mitosis, and that this phosphorylation is required for its activation.