second cyclin box found in G1/S-specific cyclin-E (CCNE) family
The CCNE family includes two E-type cyclins, CCNE1 and CCNE2. 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. CCNE2 is essential for the control of the cell cycle at the late G1 and early S phase. It interacts with the CDK2 (in vivo) and CDK3 (in vitro) protein kinases to form serine/threonine kinase holoenzyme complexes. Members in this family contain two cyclin boxes. This model corresponds to the second one. The cyclin box is a protein binding domain.