first cyclin box found in G2/mitotic-specific cyclin-B1 (CCNB1)
CCNB1 is essential for the control of the cell cycle at the G2/M (mitosis) transition. It is required for embryo development. Over-expression of human CCNB1 has been found in numerous cancers and has been associated with tumor aggressiveness. CCNB1 contains two cyclin boxes. This model corresponds to the first one. The cyclin box is a protein binding domain.