first cyclin box found in G1/S-specific cyclin-E1 (CCNE1)
CCNE1 is essential for the control of the cell cycle at the G1/S (start) transition. It interacts with CDK2 protein kinase to form a serine/threonine kinase holoenzyme complex. CCNE1 contains two cyclin boxes. This model corresponds to the first one. The cyclin box is a protein binding domain.